Overheating??

[sheldonsmith]

Enjoyed a track day at Miller with my new R8 last Monday. The little tach symbol comes on occasionally and limits the rpm to 6000. It's a pain in the neck. The Owner's Manual says that this symbol means "Engine Overheating." My temp.gauge reads a quarter below the red line.

Any comments????

[willyjp]

Enjoyed a track day at Miller with my new R8 last Monday. The little tach symbol comes on occasionally and limits the rpm to 6000. It's a pain in the neck. The Owner's Manual says that this symbol means "Engine Overheating." My temp.gauge reads a quarter below the red line.

Any comments????

Water temp or oil temp?? I have NEVER seen my water temp beyond the middle (straight up) of the gauge, despite some fairly hard driving in hot weather. I have gotten the oil temp about 2/3rds of the way up to the red line, but never seen the rev limiter. Was the air temperature pretty hot?

Is it a new car? My oil runs cooler now (10k mi.) on hard driving than it used to.

[desperado]

How hot was the outside air temperature on the track? [Never mind, I just looked up the weather history for Tooele - that afternoon it was 100-101degF nearby (at Lake Point Estates), so it must have been even hotter on the track!]

When you say little tach symbol, are you refering to a plain-language yellow warning message on the DIS? On a day with 105degF inlet air temp on the track I did experience overheating as you describe. First you'll get one message, a temperature warning. I missed it the first time, and received a second warning message and the rev limiter moved down to 6,000 RPM. I found that upon getting the first message, simply backing off for half a lap would bring the temps back down; pushing hard would soon send both needles heading up towards the redlines and I'd get the first warning message again.

Mine is a supercharged 2009, however a stock ZR1 and a stock M3 were also overheating on the same afternoon. Sounds like last Monday was just too darn hot in the afternoon to be pushing the car so hard! I doubt you will have a problem on a more reasonable day or in less strenuous driving conditions. For example I was at Miller last month, it was 93-94 in the afternoon, and I had no issues.

If you track the car in these conditions again, I would recommend you keep an eye on the DIS and heed the first warning. I would try not to let it get to the second warning with the rev limiter, I don't know what damage that might eventually cause.

[sheldonsmith]

The air temp on the track was100+ degrees F. The gauge I was reading was water temp. It cut out at a Porsche DE day in June when the air temp was in the low 80s. These cars should not overheat under almost any circumstance. Since it did this under much cooler circumstances I suspect that something else is wrong.

[mngolfer]

Last year at Badger Audi Road America event in August we had two R8 participate in the HPDE. The the temperature was 96 degrees and VERY humid. Neither of us had any overheating issues. There must be something wrong with your car. A trip to the dealer should be scheduled IMO.

[willyjp]

Last year at Badger Audi Road America event in August we had two R8 participate in the HPDE. The the temperature was 96 degrees and VERY humid. Neither of us had any overheating issues. There must be something wrong with your car. A trip to the dealer should be scheduled IMO.

Yeah, I'd be concerned a bit because my v8 has never seemed close to "too hot" despite working pretty hard under 95+ conditions. I'd get it checked, but I'll bet you everything is OK and that it was just because your car is brand new...and the air temperature unusually hot on top of it.

My car was delivered in September and I recall it heated up fast and ran as hot as I've ever seen it during moderately hot Indian summer weather when it was in it's first 1000 mi or so. Lately, it seems you just can't drive it hard enough to make it overly hot.

MNgolfer's mention of humidity raises an interesting question: at a given ambient temperature, which cools an engine better? Humid air or dry air?

No question dry air FEELS cooler TO US. But we're cooler than the air and we depend on evaporative cooling for a very large share of our heat loss, unlike an engine which depends on radiation and convective transfer to the cooler air bathing it and it's radiator.

Seems to me that humid air, having much more water, with its high specific heat, which provides a tremendous "heat-sink" capacity", ought to be a lot more effective at cooling a hot engine than dry air (which I assume is what was present in spades @ the altitude of Miller Motorsports Park when it was 105℉ or whatever it was out on the track).

Just random speculation, not that it makes a whole lot of difference. My atmospheric physics and mechanical engineering may be a little weak here...my cooling system training is limited to biological systems!!

PS: I just re-read the thread and realized I missed some of your reply posts, which, now that I've read them, change my opinion! Glad I caught them. I WOULD be more concerned about this because you had it before, and at lower temps. So the car isn't as "brand new' as I was thinking. Also, my experience with hotter temps during "running in" (which I did pretty "hard"), was with OIL temps. My car, as I said above, has NEVER, EVER run a water temp. above straight-up, mid gauge despite autocrossing and tracking in the '80's and very long and hard running uphill in the mountains in the '90's. So I would be a little concerned about your (water) cooling system. Did your oil temps run inordinately high during these overheat episodes?

[willyjp]

Did a little research on humidity and density altitude as they effect engine cooling. No question, at Miller at 100+ and 4400' above sea level, you had a combination of negative factors affecting engine cooling: lower air density, (probably) low humidity and high ambient air temperature. Googling on "effect of altitude on engine cooling" and "effect of humidity on engine cooling" turns up some interesting stuff.

No question, other things being equal, humid air cools a hotter object (absorbs heat) better than dry air. But your "density altitude" at that elevation and temperature was LOW! My old Cessna 172, fully loaded, probably would have needed 2500' to get off the ground on that day! (didn't actually calculate it guys...that might be slightly high!) And that same air just wouldn't have cooled your engine as well as it should!

[desperado]

The air temp on the track was100+ degrees F. The gauge I was reading was water temp. It cut out at a Porsche DE day in June when the air temp was in the low 80s. These cars should not overheat under almost any circumstance. Since it did this under much cooler circumstances I suspect that something else is wrong.

I agree. There seems to be something amiss.

[sheldonsmith]

I tend to drive my cars and it has 6000 miles plus on the OD. thanks to everyone's comments. I'll check with the dealer and let you know.

[Moggy]

No question, other things being equal, humid air cools a hotter object (absorbs heat) better than dry air.

I'm going back nearly 30 years here, but I think my memory of my heat transfer courses are reasonably accurate.

Although they're called "radiators", I think the main method of heat transfer is conductivity. Incandescent light bulbs radiate heat from the filament as they have a vacuum inside the bulb. Water is a much better heat conductor than air. That's why scuba divers wear neoprene wet suits in 83 degree water and shorts on the beach. So it makes sense that air with more water in it (i.e. more humid) will transfer heat away from the radiator more efficiently.

Ambient air temperature comes into play as the greater the temperature difference between two areas, the faster the heat is conducted.

The main thing I remember from my heat transfer classes is actually calculating the rate of heat transfer created some of the hairiest simultaneous partial differential equations that I hope never to see again!