Lost 3.6 mpg, what'd I do???
 

My blazer is running great, no engine light, just as smooth as it always is.The only difference between this fill-up and the last was I just changed the oil. 5w-30 conventional was used (which is what was in there before). I've never had this bad of a mpg, went for 19.2 last week to 15.6 this week. Previous worse was 16 last winter. Tire pressures are all at 38psi as always. Tune-up items all have less then 10k miles on them. I'm I possibly accelerating TOO slow???

maybe an oxygen sensor or the EGR valve. I know my EGR was getting clogged and I lost a few miles per gallon and couldn't figure it out. my engine finally threw a code.

I have actually found that if you briskly accelerate to get up to running speed, it is actually better for your efficiency. just stay out of WOT and also close to WOT as to not go into open loop. that is where the ECU will just use a preset fuel map and just start dumping fuel in the motor. I have had pretty good success with doing this.

I lost 2 MPG after getting my radiator flushed. I'm not sure that it is related. It is a bit of a guessing game for me with regard to effectiveness of some of the techniques without my scanguage. I am so looking forward to that instand feedback.

CHVYPWR, with an automatic it can be inefficient to accelerate too slowly; with a closed throttle and low RPM, the transmission may wait in a low gear instead of shifting when it should, and it may not lock the torque converter until you're in high gear. Sloshing the ATF in the TC can waste energy.

Brontegirl, your radiator may have been clogged and not working as well, which could increase fuel economy in some circumstances...but it's still better to have it working right.

How much have the temps and winds changed since your last fillup?

I know here in MN and WI the winds this last week and the temps have been really cold and windy. It'd hurting my mileage as well.

Well, I'll try giving it some more pedal then. The trans does like to hang a little before shifting, if I let off it shifts, or give it more it shifts (a typical 4L60E). The lock-up kicks in at 45mph no matter what.

Temps for this tank were still summer like. I hadn't drove it over the weekend when it got cold out.

Well, while I'm logged in, I figured I'd ask my wife if she filled up the Jeep yet. She did, and her fill up was 3mpg lower too!!!! I'm thinking they must have started with the winter blended fuel here in Michigan already! :mad: :thumbdown: The Jeep has been rock solid at high 26 to low 27 since we got it in April. A change in fuel seems to be the most logical idea for both vehicles to drop like this. Thoughts?

no idea about winter blend fuel but i'd change the fuel and tranny filters(and tranny fluid of course), especially if it's been a while. the only thing i can think of besides tune-up, which you already eliminated.

my wife's chevy w/ AT seems to get sluggish when those services get neglected.

I track every tank.

start w/ the fuel filter. it's incredibly inexpensive and very simple to change on a chevy truck.

the tranny service needs to be done at some point, so if it's due...

clencher could be on to something. i looked at the recorded, yet very limited fill-ups and the previous 19.2 mpg in a 4X4 could be a stretch. and the recent fill just balanced an inflated number.

The trans fluid is pretty fresh. I have a slow leak in the transfer case input seal which allows fluid to flow from the trans to the t-case, so I'm adding a fresh qt about once a month and draining the t-case down also. I have a seal, just havn't had the time yet. But, a filter change is going to get done soon, probably the same time I do the seal.

So, short fill-ups arn't good practice for FE huh? Well, thats good info, I'll keep that in mind.

Disappointed in my mpg, I went out tonight and installed a 75% grille block. I'll have pics of that up tomorrow.

run another tank or two and see what you get then.

Short fills aren't terrible, but they don't give you useful data like a fill from empty does. You have to average a lot of them together before their data becomes meaningful.

Good to know!

Heres my post on my new grille block: https://www.gassavers.org/showthread....423#post142423

How's your oil level? An overfull, or fully filled crank case uses more fuel than a half hash mark oil level. Jim

I recently had a 1 MPG drop off after three tanks of 18.9 MPG. Asked Leon, who runs the Costco station about Winter Blend and he said my mileage should increase with it. But we don't have it here yet.
Supporting OPEC to the tune of $40.00 or more a day, I've gotten pretty good at the art of topping off, but as the experts previous to me have said, as complete a fill as possible is most accurate, as is more than one tank of gas.

With all due respect to Leon, up till now I've only seen and heard of mpg dropping off with winter fuel mix and coming back up when we go back to the 'summer' stuff. I track mpg with every fillup and I've seen it every year since I started in Feb. '07.

I'm sure some of the winter decrease is due to sucking off engine heat to stay comfortable inside the cabin. But I think the fuel change is a big part of the reduced winter mpg's I've seen.