Oil Temperature: an altitude question
 

I did quite a few searches on 'Oil Temperature' and 'altitude' but didn't find anything relating the two. Common sense might say that at Denver altitude the oil temp will be higher than the same car at sea level (at the same outside temp).
Anyway, it's been close to 100 degrees in Denver the last week and my oil temp goes to between 9and10 on the gauge in traffic.
The car is a stock 96 C2 and the fan works, high and low. I think I'll set the fan to permanent high for summer and maybe invest in the brake scoops without the plumbing.
Any other suggestions to keeping oil temps at or below the 9 level?

My car does the same thing. I asked the owner of a well known 911 racing team who sometimes services my car if I should put the manual fan override switch in. He said he'd love to make an argument to take the money for the work but he said would feel bad because he believes it's really not necessary. This is after I told him my temp gauge goes to about "9:30" when it sits. Yesterday, in heat approaching 105 I was driving the car on my return from San Diego and was moving at a really good clip. Not that I will admit to specific speeds :evilgrin: but these cars move through the century mark with such ease it's easy to find yourself zipping along. Nevertheless, in that heat, and at that pace, the oil temp gauge was a smidgen over 8 o'clock! And one of my fan resistors is bad. The minute she becomes stationary she goes right to 9:30.
Other than the fan, aux oil coolers seem to be the most prevalent option.

If this really was common sense, wouldn't you run hotter than 98.6 in Denver? Temperature is just a measure of the average kinetic energy of the pieces of the material measured on a known scale. 100 in Denver is 100 in San Diego. Where elevation comes in to play is when the material tries to change states. Denver has a lower barometric pressure than San Diego. Therefore, liquids will change state (boil) at lower temperatures in Denver. Hot is hot, no matter where you are.

The less dense (and very dry) air in Denver is less effective at cooling the engine and oil - that's a fact. I can't give you the science though...

Yup. You can see this for yourself if you take a bag and fill it with air in Denver and then take it to L.A. The bag will collapse because there is more air in L.A. This is Air Density. It is why we can take off at much heavier weights in LAX at 100 degrees than you can at DEN at 100 degrees. The wings are less efficient because of the lack of air. The engines (fans) also don’t produce nearly as much thrust.

Tom

I couldn't give a scientific explantion before, but I think that I can now. Just as more massive brake rotors have a higher thermal capacity than less massive ones (more mass of the same material is a better heatsink), the higher mass of air that blows over your cylinder heads and oil cooler at sea level can absorb (sink) more heat than the thin air in Denver.

You all are right, but he didn't ask about any of your answers. He asked if "at Denver altitude the oil temp will be higher than the same car at sea level (at the same outside temp)." He did not ask about the density of air at elevation, cooling capacity of moving air, or heat holding capacity of air at different pressures. He also did not ask if a car in Denver would run hotter oil temps with engine running if air temp and air velocity were equal (which, I think, is what he wants to know). My answer was specific, and smartass.

Velocity of air is the key to cooling since less dense less humid air has less heat holding capacity (as stated). To keep temps equal, you need to move more air. Or, I remember rigging the windshield squirter to mist the cylinder heads on my old SC when it got hot. Worked pretty good.

The short answer is it depends.

The heat capacity and heat transfer rates of the air along with the heat output of the engine are the key components here (assuming equal engine throttle settings, air temperature and air/fuel mixture).

At one extreme you have high humidity at low elevation compared to high elevation with low humidity. Although, a person may feel hotter in high humidity, car engines don't sweat, so the difference to the engine is that humid air can absorb more heat, but humid air leads to lower power (compared to dry air). Air pressure has a similar effect. Higher air pressure makes more power and heat, but also provides more cooling (assuming identical throttle settings).

Now on to common sense. You engine is more likely to overheat in the dessert at 100F than in the rain forest at 100F.

Geeezzz! :confused: The only question he asked was the sentence with the QUESTION mark after it. Everything else he stated, was just that....a statement. If you re-read his post, he asks are there any other suggestions (besides the fan) for keeping the oil temps at or below the 9 o'clock position, which was answered in my initial response....i.e., an aux oil cooler. Everything else in this thread is related to analyzing and questioning his statements/reasoning that led to his question. C'mon guys. We don't need calculus to do arithmetic.

IMHO, the only way to control oil temps in your situation is to install an additional left-side oil cooler to double the thermal dissipation capacity. I would also offer that its cheaper than dealing with the resultant oil leaks from running at those elevated oil temperatures.

Everything else is just a band-aid. :)

I received the bogus altitude explanation from my dealer when I bought my car in Seattle and drove it home to Albuquerque (same elevation as Denver). My temps routinely went above 9 o'clock even though a friend's 993 under the exact same conditions would never go above 8. I didn't believe their explanation could explain such a large difference. After further diagnosis, I found my oil thermostat wasn't opening properly. This eventually became obvious because although the fan worked (after I replaced the resistor, anyway), the oil cooler in the front passenger fender never got hot. Do a search on "oil thermostat" and you'll find that this has been happening to others also. I don't doubt that an auxiliary oil cooler is still a great option, but I suspect your thermostat may be on it's way out. Mine went gradually and it was only when it was out for good that I caught it. This is a relatively cheap fix.

Paul

+993 on Steve's response... my gauge reports below 9:00 consistently since I installed a Ruf cooler... even at a standstill, even in our lovely 115 deg F heat this week! Previous to the aux cooler, the temp would climb right past 9:00 at stoplights with the fan on low speed... only the high fan switch or getting up to speed would bring it down.

Thanks for the responses. And thanks for the analysis. My thermostat does open and I assume it's either open or not with no partial openings.
The aux oil cooler would also help delay the inevitable valve guide wear problem.

FWIW, I haven't seen my gauge "above" 9:00 in DEN traffic recently. I do make sure I keep my oil level up. The temp drops significantly (below the 8:00 mark on the freeway [>60mph]) even with a split/partial spoiler wall.

Maybe it's my imagination, but I was running 15-50W until the local $tealer replaced it with 0-40W at my 30K service - I never noticed temps above 8:00 before then. May be my age . . . . :)