Why do engine and trans temps increase at higher elevations ?
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Joined: Jul 2007
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From: Fairfield California
Why do engine and trans temps increase at higher elevations ?
I just got back from a great run through the Sierra region of Northern Cal and I noticed at lower elevations 50' - 1000' ft my engine oil temps fluctuated between a normal range of 228-232 degrees, coolant temps between 192-202 degrees and tranny temps between 185-200 degrees. The higher elevations on the other hand ( 4000'-6000') yielded the following temps : engine oil 240-245 degrees, coolant 205-216 degrees, trans temps 200-212 degrees. The ambient temperature varied between 80 and 85 degrees and the car was driven at a moderate pace, I kept the revs between 1500 and 2500 rpms while in third gear most of the time. I realize the higher temps are at the high end of normal and really nothing to worry about, but I'm somewhat old school and just like to see cooler temps. The main point is why would higher elevations cause significant temp increases and this is not the first time I noticed this. My car by the way, is a cammed 2005 A4 with 3.73's. Thanks in advance for any insight you all may have.
Safety Car
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From: Austin, TX
The cooling of the engine and tranny are more complicated than this but fundamentally the previous poster pretty much hit it on the head. Altitude definitely affects convection cooling capacity due to the reduced air density. This means that anything that depends on moving air to provide cooling will in general have higher temperature rises. In addition to that, the radiator fans are affected as well. For a given RPM they will move less air so its a double whammy. This being said I think that the fans would just stay on longer to compensate but I'm no expert there.
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Racer
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From: The Villages FL
To begin with none of the temps that you reported are out of line. Your cooling system is performing great. Your engine oil temps showed the most heat input into the system. I'm guessing that the terrain was variable and you were climbing grades. That would elevate your engine oil temps and cause the system to stabilize at a slightly higher temp. Usually when climbing grades the ambient temp drops 3 degrees per 1000 foot of elevation thus offsetting to some extent the change in air density.
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St. Jude Donor '08-'09-'10-'11
My temps are the same at 6800 feet as they were in NY at sea level. I see 176-178 for coolant with the 160 stat as it was at sea level. There is no difference from thinner air.
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From: Fairfield California
Spin, interestingly enough half of my friends who went on the run with me note very little change in their temps. The other half noted elevations in temps similar to mine. I see that you have a 160 degree thermostat, mine is the stock 195. Would running a cooler thermostat help to cool things down a bit ?
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St. Jude Donor '08 thru '13
Higher elevation = lower mass air flow (for a given volume, less air molecules) = less mass to carry away the heat.
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From: Fairfield California
Good question, I had not thought about that. I do know that my friend who has a 09 A6 reported temps slightly higher than mine but another who has an 05 A4 stated his temps were lower. I can't definitively say whether having a manual or auto made a difference in operating temps.
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From: Greater Detroit Metro MI, when I'm not travelling.
Are you sure the temperatures weren't higher up because you were climbing? It takes a lot more power to go up a hill than to drive on a level road; that'd explain why the oil temp is so much higher.
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St. Jude Donor '08-'09-'10-'11
By the same thinking there is less air to resist your car movng forward, lowering inertia.
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How much variation do you see with differing ambient temperatures?
