Cylinder head temp vs oil temp in traffic

[silvercar00]

A summer traffic jam really seems to put the fan/engine tin engineering to the test. I have a condition right now which I believe is a faulty Cylinder Head Temperature Sensor and it will run rough and actually shut down like a rev limiter and stall at RPM's above 3K after I've stopped at several long traffic lights, but if I go on a different sort of drive....long highways with no stops....it runs perfectly at all RPM's with the gauge reading the same approximate OIL temperature. I'm supposing that the fresh air flowing over the cylinder heads is the difference by lowering the Cylinder head temp ( again pointing to the CHT) Here's my question: This lead me to think about the fact that most 911's are in California, (and I've actually been in hot weather LA traffic jams myself as well those in as Phoenix, Las Vegas) and I've got to think that this must be absolute murder for these engines.....or am I wrong here...are they built for that?

[Jack Olsen]

I have a CHT gauge on my car, and I don't see elevated head temps in stop and go traffic (although oil temps do rise in those conditions, since there's less airflow to the coolers). I do see the head temps rise and fall in 'spirited' canyon driving. But I've seen my highest CHT readings in steady-throttle driving under load, like a long mountain incline. Oddly, this is when there is a lot of air moving over the heads.

I don't know if that's helpful with your problem, but it's a data point for you.

[Grady Clay]

Unfortunately they are built for that – sorta.

A 911 engine will withstand incredible abuse. It isn’t necessary and is counter productive to engine longevity.

As Jack says, it is driving dependent.
Jack, what do you have for cooling?

By ’69 Porsche recognized the need for a front oil cooler on a 2.0 911S. In ’75 they were constrained with noise regulations. Through too many years the bean counters also limited the engine cooling.

Here we are 20+ years later re-engineering our 911s. What to do?

Install the 1.82:1 engine fan. Install the largest thermostat controlled front oil cooler(s) with electric fan(s). Pay attention to your engine temperatures. Too much heat is a killer.

Many suffer this undetected abuse because great valve stem seals prevent oil passage and of catalytic converters burning the excess oil when the guides fail

Best,
Grady

[Jack Olsen]

Originally posted by Grady Clay
Jack, what do you have for cooling?

I have a Carrera cooler in one fender and Turbatrol cooler in the other. (I did not add an engine-mounted cooler in my 3.6 in the power steering spot, as some do.) One cooler has a fan, and both are ducted. Oil temps are not a problem, but they'll go up from about 180 to as much as 210 in stalled traffic. Switching on the fan brings things back down without a problem. I mentioned it only because I've seen oil temp increases without corresponding CHT jumps in stop-and-go driving.

[Emission]

Originally posted by Jack Olsen
One cooler has a fan, and both are ducted. Oil temps are not a problem, but they'll go up from about 180 to as much as 210 in stalled traffic. Switching on the fan brings things back down without a problem.

Jack,

I saw my oil temp hit 250 at Buttonwillow last week after about ten minutes on the track (ambient temps of ~110 F. - damn hot). Slowing down (off the boost) my temps would drop down to 220 F. and I would then pull off the track and wait for the next session.

I have a Carrera cooler in my fender without a fan. Mine is ducted, and blocked underneith to keep the air from spilling around. Since the air is moving through the cooler at speed, I don't think a fan would help me at all on the track. The only time a fan helps is when your vehicle speed is <20 mph... right?

- Mike

[Jack Olsen]

No. At least on my car, the fan always helps. I run it all the time at the track. If I don't, my temps are higher.

Here's some speculation. Even with big holes in the bumper and ducting, I don't think a great deal of air is moving through the coolers. I'd guess that the air moving across the front bumper is moving laterally as much as it is hitting the bumper head on, and I suspect the air that does make it in creates a high pressure zone, resisting against additional air coming in behind it because -- get this -- the area in the wheel well is also a fairly high pressure zone (even though it seems like it shouldn't be).

Or at least, that's my uneducated guess. Obviously, a fair amount of air does move through a fender-mounted cooler; my cooling got more effective when my ducting went in. But I think the volume of air is only a fraction of the amount that would move through a well-ducted center-mount cooler in the bumper.

In any case, even with big inlets, ducting, and a clear path for the air, my system still works better with the fan.

Air management in the fenders was improved with the 964 design, and I think it got even better with the 993.

[juanbenae]

i saw more effective duct cooling after installing a chin spoiler.

[Emission]

Originally posted by Jack Olsen
No. At least on my car, the fan always helps. I run it all the time at the track. If I don't, my temps are higher.

That statement, and the fact I had to park it on the side of I-5 on the return trip home and wait for it to cool after temps hit 250 while idling on the Grapevine (SigAlert shut down nearly all lanes) is reason enough to add a fan!

I think you are right about the wheel well being high pressure. It may explain why brake dust goes "out" and coats the wheel. It would work counterproductive to a forced-air-fed oil cooler.

[randywebb]

not hard to measure the windspeed behind the cooler...