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Old 07-18-2007, 06:20 PM   #1
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Underhood temp after varying levels of grill blockoff

Howdy, I'm new here. And yes, I probably have way too much time on my hands. But I live in the desert and have a need to know.

Sometime within the next few days I plan to cover the grille in my car ('93 Geo Metro, 1.0, A/T, A/C ) in stages and measure both water and underhood temps with each successive degree of closure. I'm hoping that my particular vehicle can tolerate completely blocking off the grille area and rely on the small slit of air entering the front lip of the hood.

Local temps have been hovering near 100+ degrees lately, so the results of this should provide a fairly good "worst case scenario."

Given that the car itself , (by virtue of its air conditioning and automatic trans), may not exactly be the first choice for mileage maniacs, and also given that by virtue of its a/c condenser its underhood air circulation may differ from a non-a/c equipped car, my questions is:

Since I'd like the information to be of at least general value to others and of particular value to Metro mavens, what area of the engine compartment should I monitor (a single K-type thermocouple in free air) which will provide the most meaningful results?

I plan to monitor the temps at idle for 15 minutes after each change. If there are no signs of overheating I will drive the car on a 2 mile loop and return. The car will remain idling while changes are made to the grille openng, and then the process repeated.

Sound "scientifical" enough?
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Old 07-18-2007, 06:39 PM   #2
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I would like to make two suggestions. Make sure that somewhere on your loop that you get up to the max speed that you would normally drive your car at. Hold it there for as long as possible. You might also think about increasing your 2 miles to something a bit longer.

I would really be interested to see your results, with temps and as many details as possible!
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Old 07-18-2007, 07:59 PM   #3
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I just composed this lengthy and verbose diatribe about excess heat and Suzuki alternator failures, solar flares and aluminum foil hats, et al.

Fortunately, it was lost.

My primary interest in posting was to hear suggestions on where to place the thermocouple for reading the underhood temps. Barring any other ideas I'll just use the air cleaner nut as the attachment point.

The way I see it this is a "pre-experiment". The initial temps will either be cause for alarm, or they won't. If they aren't I'll procede with some longer distance testing.

I save gas that way, no?
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Old 07-18-2007, 08:08 PM   #4
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Hmm, what's wrong with the coolant temp gauge? Why do you care how hot the air filter nut is?!?
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Old 07-18-2007, 09:27 PM   #5
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There's potentially more to consider when blocking a grille than just groovy MPG and aero numbers.

The aforementioned Suzukiclone alternator failures, for example. I'm convinced that the high incidence of failure is due to the already poor location of same. And all those plastic pcv valves and electronic gizmos under your hood won't be sending you a Christmas card if they're dead, either.

Water temp alone means nothing, at least in the case of the Suzukiclones. Most folks do a grille block on them with the openings on the LEFT (radiator) side where the heat and air are free to spill over the low transmission and under the car or wherever it is that they go. Whatever their path they can't really escape cooling the radiator in that situation.

What we don't know is what's happening on the other side of the engine compartment. I'm willing to bet my next date with a supermodel that the area behind the motor is where all that heat really goes to stagnate Ever touch a Suzuki alternator after you've driven for a half hour or so?

A car that doesnt run gets ZERO MPG, dispite its Cd

Lotta noise for a newbie. Sorry.
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Old 07-18-2007, 09:37 PM   #6
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Yah, but it's a 93 metro!!! FYI, my alternator came with a wedge of wood I have to hammer on occasionally to re-tighten the belt

I'm sorry, I'm supposed to be nice to the new folks. If you don't believe the coolant temp gauge, then oil temperature would probably be worth monitoring and air intake temp. And the automatic has a cooler up there that isn't going to get air either.
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Old 07-18-2007, 09:57 PM   #7
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Ya gotta be nice to me, but you don't gotta be nice to my ideas. There's a
difference.

I'm thinking that by some combination of openings to both sides I can both cure a design defect and generate some aero advantage. Just thinkin out loud, but this forum is for actual experiments. Sorry.




BTW, I picked up the alternator adjusting arm from a Misubishi today. It has an incremental screw adjustment on it, has the same offset as the Suzuki arm and is for essentially the same alternator. It should eliminate overtightening of the belt, which is the other cause of failure on these cars. Just play with the throttle while you're ajusting it with a screwdriver just to the point where belt squeal is liminated.
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Old 07-18-2007, 10:18 PM   #8
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And you mentioned AC, there is probably a big condenser by the radiator (along with the automatic trans cooler) that isn't going to get air. I'd leave the air off, or not expect much out of it anyway.
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Old 07-19-2007, 12:26 AM   #9
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Did a little check of my theory in my driveway this evening.

I hooked thermocouples to each shock tower so I could check temps. Both sides of the engine compartment were within a few degrees of each other (approx. 155 degrees) during fan/off operation.

Predictably, the driver's (radiator) side temp rose by nearly 26 degrees when the fan cycled. The passenger side rose by only 7-8 degrees. However it took nearly twice as long for the motor side to dissipate 7-8 degrees than it did for the passenger side to dissipate 30 degrees. The air is getting trapped in the right rear between the firewall and the motor. So I guess the shock towers may be a good place for the probes and also that you W.A.I. types should turn your snorkles around.

Er sumpin.

Anyway I'll let you know if it holds true when the car is in motion and whether or not the grille blockoffs exacerbate the situation.
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Old 07-19-2007, 08:55 AM   #10
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Here is alink to a really informative site that everyone on this site should checkout, they have done quite afew tests on aerodynamics, underhood effects of all sorts and tons of more useful info. This will definitely help with your question about underhood temps and ways to alter it, YOU WON'T BE DISAPPOINTED

http://autospeed.drive.com.au/S_3/cms/section.html
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