Modifying my Brick-On-Wheels
 

Hey all,
I have a 1994 Ford Explorer, and I've recently been doing a lot of research on these forums and Google on aerodynamics. Considering my Explorer is essentially a "Brick-On-Wheels", I'm attempting to modify the aerodynamics with a shoe-string budget.

Yesterday I removed the roof rack bars (the tracks are still in place), and made a 'nose' for the front that essentially blocks the huge grill opening. I installed that tonight, along with a make-shift air diffuser thing on the back. I think that's the wrong term tho. It's basically a folded piece of duct tape that's taped onto the rear of the roof.

There are still openings in the bumper for air to get to the radiator (but I did tape one up to block it off).

When I get some time, I'm hoping to at least do a partial body pan to help get air around the front differential (which is huge), along with filling in all the gaps I can on the underside to help reduce drag.

I'm looking for help on all of this. I need ideas, constructive criticism, and help with figuring out angles etc. for the best nose design.
Currently, my 'nose' is made from an old poster, some wood for support, and duct tape. :)

Here's basically what my explorer looked like before (except I re-installed the stock air dam):

https://www.gassavers.org/attachment....1&d=1257300150

And this is what it looks like with the nose:


https://www.gassavers.org/attachment....1&d=1257301052


https://www.gassavers.org/attachment....1&d=1257301052


And this is what that "diffuser" on the rear looks like:

https://www.gassavers.org/attachment....1&d=1257301052

I took these on my phone, so they aren't that great... but they work.

My last fill-up was 13.48mpg. That was like 95% city driving. This tank I had also drastically modified my driving style (taking it easy on the gas, going the speed limit, anticipating, etc etc). I also blocked the cold air intake portion of my air intake, so now it only sucks air in from around the exhaust (this is a stock setup, I didn't modify anything, except for blocking the cold)

My fill up before that was ~10mpg. So, an improvement for sure.

I think the 13.48mpg tank would have been better, but there were excessive detours which left me idling for a long time (it's a 2-mile drive to campus [college student], and it took me 30 minutes ... needless to say, I was about 10 mins late for class most of that time). Finally, almost all of the construction is done so no more detours (YAY!).

I mainly only do city driving ... but I'm mainly doing these mods for the 1,000 mile trips I take to go home for breaks (round trip).

My EGR valve is blocked off because it is stuck open ... but that'll cost over $200 to fix and I can't do that right now. Considering I got the best gas mileage ever (but only on a ~60 mile trip) on the "highway" (21.4mpg, 55mph) with the EGR blocked, I don't know if the EGR valve was really doing much anyways before, other than reducing emissions. Don't flame, I really want to get it fixed ... but it's $$.

Winter city driving, I average 10mpg ... lots of snow & frigid temps (20F to -20F), and I have my front hubs locked all the time so I can engage 4-wheel drive "on the fly" without stopping.

Just thought about adding some info. I write a lot, sorry about that.

Slow down...by doing dozens of vehicle and driving modifications all at once, you won't know what worked and what didn't. Also, you will need to try to get a lot more data than one tank. You need a few steady tanks as a baseline before you can accurately tell the difference when you try something - and then you need a few tanks with it to be sure.

I very much agree with what the cow said, But i must say I like your approach to craftsmanship.
With this project it is important to think about all the variables.
The aerodynamic aspect of the grill may be making no difference and any improvements are from covering the radiator.
the speed your are driving at will make a huge difference on any gains or losses in aerodynamic performance, so to make any comparisons things have to be nearly equal.

Yea, I know :o
The problem is, I usually only go thru a tank of gas once every 2-3 weeks because I mainly do city driving. I also don't have a garage, so I'm trying to get stuff on it before snow sticks (the snow is already flying up here...but not sticking yet).
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I just got back from a trip to Calumet and back. Same route as before (I posted about it on one of my other threads re: EGR valve, etc). Up here, it's a "trip". Almost nothing is more than 4 miles away before you leave the city. Round trip, it was about 27 miles. about 5 of that was city driving without the mods. I got ~17.4mpg.
If I did the math right, about 25% of the gas consumed was due to the city driving ... thus giving me approx 21.43 mpg hwy ... as a VERY rough estimate. I don't even know if I can assume that. If it can be assumed, there'd be no change in gas mileage.

I know 27 miles isn't very far for testing ... but I can't do much more than that, at least for highway. I'll be driving to Marquette this weekend, two hours each way. I'll keep track of the mileage for that and see what it says ... though, I can't duplicate it for future tests unless there's a reason for me to drive to Marquette (that's where the closest Lowe's is).

All of my highway testing is done at 55mph (the speed limit)

You posted as I was still typing my post :)
I do the tests at 55mph, with very little of that being below 55 to get to the "highway".

For winter, I generally always block the radiator. Last year it didn't seem to do anything for my gas mileage, but I wasn't driving as light as I am now either.

In my experience trying aero mods on my GMC Sierra K1500, aero mods don't work on trucks in an urban environment. If you had more open road / highway driving then I'd say you can have at it with the body pan & everything. Sure it does something, but I think for your investment in time & materials you are better off looking somewhere else than aero.

1. Driving with the hubs locked is a big hit. I would recommend leaving them unlocked, and only lock them on days where poor road conditions are expected.

2. A grille block would be good, but not as much for aero reasons, but to help keep the engine warm. I'm not sure how the intake air is routed on that vehicle, but if it is drawing in cold air from outside, disconnect it so its drawing preheated air from the engine bay.

3. You may also want to investigate rigging up a warm air intake, and intentionally preheat the air (usually by moving the air intake near the exhaust manifold).

4. Make sure your vehicle is running in the best condition possible. This means that all fluids are checked/serviced regularly. Synthetic fluids can help boost mileage. When was the last time the transmission fluid was changed? The transfer case? Differential? Engine oil? These can make impacts on your mileage if neglected. This also means you should get the EGR fixed. Have you looked into the possibility of getting an EGR valve from a junkyard? In my area I've dealt with several U-Pull-It yards. You go in, pull the part yourself, and in the end they'd probably only charge $10 or $20 for an EGR valve.

5. Take a look at your tires. Are they the proper size, or does it have bigger tires than the factory put on it? What about your tread? Are you using a tire with a highway tread, or an off-road tread? Smoother highway tread patterns on your tires will help with mileage as compared to off-road tires. I would recommend either an A/S (All Season), or a M+S (Mud & Snow) tire. AT (All-Terrain) tires usually have an agressive enough tread that mileage will be effected. Ford usually puts M+S tires on all their trucks at the factory.

6. Most importantly, your biggest gains to be found will come from modifying your driving style.

The mileage on my K1500 may not look great, but consider that its an 11 year old full size, extended cab, 4wd V-8 pickup with 165,000 miles. My EPA combined rating is 13. (This is what the EPA expects the vehicle to do when driving 45% CITY, 55% HIGHWAY) I regularly get at least 13 MPG driving 95% short trip city. There are many 4x4 V-8 pickups out there that would struggle to get 10 with my combination of age/mileage/environment.

Good luck, and keep us posted.

-Jay

Good points, Jay.

I'm not sure switching to all synthetic fluids will ever pay off in fuel economy gains, even if it's time to change them anyway. Synthetic fluids can be expensive.

My K1500 is another example for comparison. 8 year old model, 186,000 miles, 4x4, V8. My driving is not urban; it's ~40% highway and the rest is town and country roads - not as stop-and-go as urban driving but definitely not highway where my truck gets its best fuel economy. I'm beating the EPA rating by a hefty amount. My only modifications are increased tire pressure and removed FM antenna.

Which is why I said it may help mileage, but certainly if the transmission hasn't been serviced in 100,000 miles that can effect mileage and longevity of the transmission. I'm merely throwing that out there as something to look at and consider.

Another thing I forgot to mention earlier was the fuel system & filters. When was the last time the fuel or air filters were checked/replaced? Also if the vehicle is old with high mileage then a bottle of BG 44k would not be a bad idea to clean up the injectors and valves.

How do you know the EGR valve is blocked?
There was a period of time when Ford had bad DFPE (I think that's the right name) sensors. It is part of the EGR system, and is responsible for monitoring exhaust gas flow. The Ranger had a bad one, and I suspect my 1996 Taurus also did. On the Ranger it was bolted to the intake manifold right up front with 2 hoses going to the exhaust. The old ones were metal, and it appeared deposits built up inside them. New ones are plastic, and run about $120 from the dealer to $60 for third party ones. Real simple to replace. The hoses are different sizes so they can't be switched.

My 93 Exploder benefited mainly from stock sized wheels, check your door or glove box to find the factory size, most people put oversized on. If its the 4.0 auto, it has a huge overdrive, so I would just keep the OD off until I reached 50 or so. The OD causes the engine to stay in eternal bog and wastes gas below 50.

I could knock 26 MPG out of if Hwy, I did run synthetic oil, I also had to switch to Dot 4 silicon brake fluid, I'd eat a master cylinder a year.

Now there is a site called Xploder.com, its a Ford Explorer site. They say that the 95-96 aero front end can be bolted on. Were talking expense here and completely removing every bit of sheet metal off the front right to the doors. If you have the room, buy a junker, or get to know your junkyard guy real well. You'll need fenders, hood, grill, bumper, and all those little bracket things. Also check Youtube and see if anyone did the conversion.

I was close to doing it on my 93, but the engine let go at 140k.

Big-Badda-Boom!

i think that synthetic fluids in all 3 parts of the drive train could yield some gains. if not fuel savings, it could save by prolonging components. and yes, fuel cleaner and filter, besides the normal tune-up.

did you pull the EGR off and clean it? my wife's car had the same issue. i actually had to apply oil to get it "unstuck." reinstalled it and no problem since.

not sure how obvious this is but...driving mostly in town requires memorizing of traffic light cycles. oh, and lots of patience--keep your foot off both the break and accelerator as much as possible.

Don't remind me about traffic light cycles... I know the order that the lights change at every intersection between home and work.

The EGR valve was stuck open, so I blocked it off myself. I'm not sure if plastic would stand up to exhaust-manifold temps. I know the EGR valve was stuck open because the engine was chugging and barely able to stay running when idle at stop lights. When I blocked it off, it was fixed instantly.

And just to clarify, it isn't blocked by something that I can fix... it's rusted to the point where it can no longer function and isn't sealed, so I blocked it to fix it being stuck open.

My exploder has Goodyear Wrangler GSA tires. I have them blown up to 40PSI (max tirewall is 45psi). Not sure if those are "oversized". It's just what the tire place recommend I replace my current tires with. Didn't care/know much about gas mileage, or how tires affected it, 3 years ago when I got them. I can't afford new ones, esp when my current ones have many years of life left.

As for putting a aero front on it from the newer models, That's not really something I can afford, nor have time to do, nor a garage to do it in. Plus, this beast has 188k on it and I don't want to invest much more money into it. Basically, if it has any major issues I can't fix myself, it's getting sold or going to the junk yard. I bought it for only $1,000 summer of 2006. I've put probably $2k of repairs if not more into it over the years... mainly nickle-and-dime stuff. Engine is still strong, so I'm crossing my fingers it'll last me 'till I graduate college.

I have been putting 0w30 mobile 1 synthetic in it for over the last year. I've been looking into switching the majority of my fluids over to Royal Purple. For oil, it'd save me money since I only drive about 5k miles a year and would only have to change the RP oil once every 1-2 years (according to the tech. I emailed at RP).

I had the transmission fluid drained and refilled by a trusted shop. They highly recommended I not have them "flush" it due to high mileage.

As far as I know, the diff. fluid and transfer case fluid are original. I was going to see about doing that soon here before full-on winter comes. I was planning on putting RP in those as well.

Traffic lights here aren't really timed. Most are based off (magnetic?) sensors in the pavement to detect when a car pulls up to the light. And... I only pass one stop light on the way to campus, and two on the way home ... the town only has 3 stop lights :) ... but lots of stop signs.

If you're putting so few miles on it that you expect many years of life from tires that you've already had for 3 years, then there is no modification (except free ones) that will ever pay for itself in fuel savings. I would suggest not to bother with fixing stuff or upgrading anything, just work on your driving techniques and continue your plan of running your beater into the ground.

Or, trade it to someone for something more efficient.

Old neglected automatics don't react well to getting too much maintenance. I'd have been afraid to even drain and fill.

I'd probably leave that alone, but if you do, check how much more it will cost to use synthetic fluids. Where I bought gear oil for my diffs recently, synthetic was hugely more expensive than dinosaur juice.

Most traffic lights have the sensor and a timer; they won't trigger without the sensor being tripped, and once it's tripped they wait for a time slot to open. However, you described a 3-light town; if the lights aren't anywhere near eachother then there's nothing to time them to.

I have a new fuel pump (my last "new" one only lasted 5k miles ...:eek:, and warrant wouldn't cover it because it was over a year from the purchase date (by like 3 months), and warranty was only a year :mad: )

I replaced my fuel filter last summer, so that's less than 10k.

I don't know what BG 44k is. I've never heard of it nor seen it on the shelves here. I usually use Seafoam (full can) in the gas tank once ever few months.

"New" spark plugs and wires already. They're like 3 years old, but that's less than 20k miles.

I had my front-passenger axle seize up about 3 years ago, along with 3 U-joints. I notices a slight decrease in gas mileage, but had no clue they were seized up until the horrible grinding noise one day on my way home (thought something horrible happened, didn't know if I'd make it the 2 blocks home). That axle wasn't replaced because there wasn't one available in the area to replace it (even at junk yards ... because they were buried in snow), they just worked it till it un-seized and greased it really well. That could be a cause for not great gas mileage. I'll have the shop check that out next time I take it in.

I can see the wisdom of not doing a power flush on the tranny if its high mileage and never been done before.

If you're already using synthetic oil I see no reason why you can't go at least a year between oil changes. The oil in my Buick (Big White Hooptie) was last changed a year ago this week. I had Mobil1 5W30 put in it. The car has only gone about 1,200 miles in the past year. I'll probably change the oil before winter sets in, but honestly I think I can probably go 2 years, but it doesn't hurt to just do it.

My K1500 Sierra (The Beast) last had an oil change a few weeks ago. I put Mobil1 0W30 in it. That vehicle gets changed every 5,000 miles. I can probably go farther, but 5,000 makes it real easy to tell when the service is due. My next service is due at 170,000 miles. This vehicle also has Mobil1 synthetic ATF in the transmission, and has synthetic fluid in the transfer case and differential.

My Chevy C10 (Rusty) was last serviced about 18 months ago. Mobil1 10W30 high mileage formula. I'd be extremely shocked if its racked up 1,000 miles since it was serviced.

As long as you're using quality lubricants and filters (Stay away from Fram AKA "The Orange Can of Death") I'd feel comfortable going 2 years/7,500 miles at least. You can probably get away with 2yr/10,000 miles with no problems - just get an oil analysis at 7,500 miles to see how well you're holding up. If you've got a comfortable margin at 7,500 go ahead and take it to 10,000 and analyze again. Once these 2 tests are done you know how far your vehicle can comfortably go.

I'm sure I can go a lot farther on all my vehicles. Even on The Beast where I go 5,000 miles between changes the truck has 165,000 miles on it and the oil comes out looking like medium to dark honey. My oil always stays translucent and never turns black.

Yea... sorry for all the posts. I didn't know how to respond to all of them in one message.

As for trading for something more efficient. Ehh... I don't think that I'll be able to trade this beast for another 4-wheel drive vehicle that's more efficient, without dropping another grand or few to compensate. I have a car too, I just don't drive it in the winter. It's much much safer up here to have 4wd or awd than 2wd. We have some very steep hills, and during the winter, the roads are basically compacted snow/ice ... covered in a 90% sand, 10% salt mixture that the plows put down. From December to late March, I never see the pavement.


The reason I got the trans. fluid changed was because it was "burned" or had a burnt smell.

For doing the diff. fluids and transfer case ... why would it be a bad idea to change them?

To change my oil, diff & transfer case fluids over to Royal Purple, it'd cost me about $160 from amazon.com (free ship ... much cheaper than local shops). I honestly haven't looked into dinosaur fluids yet for the diff & transf... just haven't had the chance yet. I doubt I'd recoup the costs for those ... but then again, I never plan to change those again. The oil I would recoup the cost ... maybe not from gas mileage, but from not having to change my oil as often.

Really?
Hrmm. Mine always turns black/dark :confused: It goes in clear/translucent.
That's why I usually change mine every 3,000 miles or 6 months. If I'm going on a long trip, I usually always change it if I hadn't changed it in the last 3 months (and it is still dark then too).

And yea... I USED to get fram "heavy duty" oil filters... then I went to the shop one day, and they had cut open all these diff. oil filters as an experiment to see which was best. They always use AC Delco oil filters... and it was honestly one of the best ones (from looks), behind like amsoil.

Need to do the air filter too, but all walmart up here carries is Fram air filters. Was thinking about a K&N, but don't think I wanna drop $60 on that (I did for my car, and it's awesome :) ). Do you have an air filter brand you'd recommend?

I don't know if it matters, but we have most of the big auto-parts stores up here (napa, carquest, etc)... There's no Autozone or that other store just like it (name escapes me).

Waste of money. You drive a $1000 beater 5,000 miles per year...it doesn't need the gear oil in the differentials changed.

Get it professionally analyzed. Most oil turns black while it's still good.

My truck is OBD-I, right? Or ODB-II
It'd be awesome if I could get a scangauge thing, but those are only ODB-II.

I saw one of the other threads on here about a DIY one using the fuel injector wire... interested in that to help out, just need the time (maybe winter break in december?).

Wix is a great brand of filter to get. They aren't terribly expensive, and they are very well rated. Usually your independent auto parts dealers will have Wix in stock. Try your local independent dealer. I had heard that WIX made the NAPA brand filters, but that was a while back. I don't know if they still do. In any event, a NAPA brand filter is probably decent quality, unless Fram is making filters for them now. K&N filters are nice, but overpriced.

Is this something any repair shop can do? ... how would I get it analyzed?

I just checked. The only 94 model Fords that a scangauge will work on are the Mustang, Cougar, and Thunderbird.

trade them both in for a junker $1200 subaru

I think most people get it done by mail. Check https://www.bobistheoilguy.com forums to find recommendations for an oil analysis company.

That might be unnecessary effort. As far as I can tell, most vehicles never suffer a failure that can be blamed on not getting the oil changed often enough (or not using good enough oil); they go to the junkyard with a good engine, a failed head gasket, a failed fuel injection system, or whatever else.

OTOH, your 3000 mile oil changes only happen once every 6 months so it's not like you're pouring huge amounts of money into it anyway...

https://www.gassavers.org/showthread.php?t=11675 :D

As HC said, black oil isn't a bad sign. It's actually a good one. The detergents in the oil are doing their job keeping the scorched oil and dirt in suspension, and not settling out forming sludge. If it worries you, put on a new filter. I did that at 6700 miles on the HHR. Along with a 1/4 quart of top off oil, noticed and improvement in the color on the dipstick. Wal-mart's supertech oil filters are a decent filter, and made by Champion Labs. The motorcraft filter might be price competative for you though. The basic Fram air filters should be fine.

My wife's Sable runs up 7 to 8 thousand miles a year. I just change the oil in the spring with motorcraft synthetic blend. A plain, certified oil should go at least 5000 miles. A 0w-30 synthetic should give you some gains in fuel economy during the winter. It just might not be enough for the additional cost.

At least check the fluid levels in the diff and transfer case. A friend didn't on a beater truck, and had a wheel come off on the highway. I've done the diff on the Ranger myself. It's a pain, messy, and the through method of removing the diff cover takes 2 days. I went with Mobil1 for it, if you are considering it.

I've looked into oil analysis. Mail in tests that include TBN analysis tended to cost more than what the oil change does for me. On a vehicle that you will put a lot of miles on, it might be worth it to initially find out just how far a synthetic oil will go.

I agree about checking the level, but how would a dry differential result in the loss of a wheel?

Yea... I'm curious about the wheel myself. Only thing I can think of is the dry diff. built up so much heat, over time it weakened the axle... causing the wheel/axle to break off. Though, that's just my wild guess, I really have no idea. Seems like the Diff would seize up before anything else. Maybe that's what happened... the diff seized up, and with the tire moving at HWY speeds, it torqued the axle, etc too much and broke it off. *shrugs*.

-------

So, before I emailed Royal Purple about fluids for my xplodr, I didn't even know there was fluid in the transfer case :eek:
4wd is important for me, so maybe I'll change that fluid... and then just check the diff. fluid levels and top them off.

What is diff. fluid supposed to look like? ... if it's no longer transparent, I'm just wondering if I should change it rather than top it off ... because don't these fluids lose their viscosity over time?

What I worry about with not changing the oil at least every 6 months is the anti-corrosion components of the oil losing their protective properties, creating havoc on my engine.

You're already using synthetic. The oil isn't going to break down that fast.

It was the wheel and axle. The diff wasn't dry, but really low. Either through the motion of the gears, most likely, or the road grade to let rain flow off, one side ended up starved for lubrication. Eventually the heat and wear snapped the axle. Being an old, high mileage beater didn't help. My friend uses synthetics in his trucks now.

The main anti-corrosion component are bases that will neutralize any acids that form during engine use. The TBN in oil analysis is a measure of much of those bases are left. Time isn't really a factor in their, and other additives, lifespan.

GM uses an oil monitoring system on their cars for oil changes. There is no mention of a mileage or time for oil change intervals in their manuals. The computer monitors things like engine run time, rpms, engine temps, and environment temps. Then it compares this data to charts of known depletion rates of oil additives under certain conditions. The lowest interval on HHR was 6700 miles. The use of EOC likely led the computer to low ball it, and the GM engineers likely assumed the minimum spec of additives in the oil.

IIRC, Ford recommended changing the Ranger diff at 100k. I did it at 60k to put in synthetic. Used Mobil1 which wasn't much more than a brand name regular oil. The truck was a daily driver, with the potential of 20k miles a year, at the time. With your situation, I don't think synthetics are worth the expense. A quality dino oil should be fine.

If you are going to change the transfer case fluid, and if they are the original fluids, you might as well do the diffs while crawling around under there. I said doing the rear diff throughly takes 2 days. Most of that time is allowing the RTV to cure. You can just suck the old fluid out of the fill plug though, and just not touch the cover plate. I think that's the only way to get the fluid out of the transfer case and front diff.

Before you start, you need to be on a level surface in order to get the correct fluid levels in. Filling can be a pain and messy do to the limited space and angles for bottles and funnels. I know that the rear diff is filled to the bottom of the fill hole. I don't know why it would be different with the front and transfer case, but I only had 2wd. If you have a limited slip diff, you will need to add traction modifier. Doesn't hurt to put RTV on the plug threads when your done.

I did both my diffs, struggling with the mess using whatever I had around the house. Then I bought this for something like $5 at WalMart:
https://www.harborfreight.com/cpi/pho...6499/66418.gif

I used it to do my transfer case and I wish I had used it for my diffs. It was cheesy but dealing with it was way better than doing it the hard way.

Cool stuffs. I'll have to get one of those pumps. It's in the automotive section at walmart? I think I've actually seen it.

I just got back from my trip. It was about 145 miles round trip from the place I filled up at (Baraga, 26 miles from Houghton/Hancock Mich... has cheap gas ... so total of ~200 miles, but gas mileage is only for the 145)

On the way there, it was VERY windy and I was getting blown all over the road. On the way back there was barely any wind at all. I also had 3 passengers... totaling more than 700lbs of weight (which includes me ... closer to 800 would be more accurate cuz I had two overweight people and two average people). Considering all of that, I got 21.81 miles per gallon. I think that's pretty sweet!

I didn't use cruise control at all, just my foot. Kept it at 55mph, didn't accelerate up hills (just kept my foot steady), and coasted down the other side usually without my foot on the gas.

What do you think?


I don't know why, but about 10 miles into the return trip, I glanced down at my temp gauge and it was just about out of the "Normal" range and by the H (Hot). I'm wondering if my thermostat stuck closed or something because the trip there it was fine. I removed some duct tape from the vents in my bumper and started driving again. About 5 miles later, it finally started dropping and returned to it's normal spot.

You may be able to save even more gas by coasting down hills instead of "coasting" in gear. Shift to neutral. Rev-match while shifting back to drive (to avoid extra transmission wear); know how many RPM you'll be turning in gear and raise the RPM before shifting. However, being old and beat-up, you might not want to experiment with things like this.

It sounds like your overheating was caused by too much grille blocking.

You had too much of the air intake blocked off, that's all, and removing the excess duct tape was the right thing to do. There's nothing wrong with the vehicle.

This is the best gas mileage I've ever gotten with this beast. I'm so stoaked right now!

I know something under my hood is going (It's been squeeling in the cold weather for the last 2-3 years [~12k miles]. After Wednesday, I'm thinking it might be my alternator cuz with the lights on, heater on full blast and radio on ... my (idiot gauge) looked like it was showing below 12 volts which is unusual. Normal winter driving for me the lights are on, heater is full blast, and radio is on. So... maybe if that's fixed I'll get even better mileage. The sound appears it may be coming from the Alt. area too, but can't tell (even with the screwdriver-to-ear trick)

I've noticed that my Serp. belt looks like it is visually getting pretty hot, like one of the bearings in a pully are bad. (excessive wear, and is now smooth on the non-ribbed side). Replacing the belt, it does the same thing.

Only reason I haven't fixed it is because I don't know what exactly is wrong.
Majority of the parts are original, or were, when I bought it in 2006 ... amazingly, the battery was the original Motorcraft as well. Only replaced it for higher CCA.

Wondering if I could get even better mileage if I replaced the alternator (if that's what is bad). I've replaced the idler & tensioner pullies last month to try and diagnose, but it wasn't those.

I've posted on [explorerforum.com] about this, and there's no real "answer". They think it's either the water pump, power steering, tensioner pulley, idler pulley or Alternator ... which names almost everything on the serp. belt except the crank.
My A/C doesn't work, so I had already taken that off the serp. (Bad clutch, I think ... it should work if I fix that).

My first thought was you had a bad belt and/or tensioner, but you've already done that. Take the belt off, and try to spin the different pullies by hand. If its a really bad bearing (which this sounds like) you may be able to tell by hand. Otherwise just replacing everything till you fix it can get expensive.