90 degree softee
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Joined: Sep 2004
Posts: 43
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90 degree softee
Yesterday afternoon in Seattle, possibly the hottest day of the year so far, I drove home from the airport and noticed that the oil tem guage ran just above midpoint instead of at the second temp mark as usual. Also, while in nuetral my oil pressure guage was at 2 instead of between 3 and 4 as usual. The motor felt soft and sluggish.
I had the fortunate opportunity to talk with Steve Weiner today because I had a question about the powerchip of his I just installed and he said the softness was a function of the outside temp and explained what was going on in the motor. Thanks Steve.
We discussed an extra oil cooler that could be installed up front. I'd like to hear from others who have gone this route and also anyone who has had similiar experiences in the heat with their 993.
I had the fortunate opportunity to talk with Steve Weiner today because I had a question about the powerchip of his I just installed and he said the softness was a function of the outside temp and explained what was going on in the motor. Thanks Steve.
We discussed an extra oil cooler that could be installed up front. I'd like to hear from others who have gone this route and also anyone who has had similiar experiences in the heat with their 993.
Nordschleife Master
Joined: Oct 2004
Posts: 7,306
Likes: 10
From: Vacuuming Cal Speedway
As one of many who live and drive in Los Angeles heat, I religously preach the benefits of the extra oil cooler and installing a high speed fan switch. My TT never sees the halfway point except 2 weeks ago at PIR racing in 108 degree heat. Even then it hit that midway point only while WOT and cooled down quickly when I exited the track. If you choose to add a cooler, get a big one not the Turbo S which is tiny....In Seattle type temps you could probably get away with just a fan override switch....
RL Technical Advisor
Joined: May 2001
Posts: 11,870
Likes: 75
From: Portland Oregon
Hi Chris:
Good talking with you this afternoon,....
As we discussed, this is a somewhat complex issue as you were feeling the results of two different things.
Elevated outside air temperatures affect two things for air-cooled engines; they reduce volumetric efficiencies due to high cylinder head temps and lower the threshold of detonation. One doesn't see cylinder head temps, but you can watch oil temperatures and they lag behind head temps at all times.
When oil temps reach 210 deg F and above, engine power begins dropping and its not a linear relationship between oil temp and HP losses. its more logrimithic. Controlling engine temps is THE key for maintaining best performance (and longevity) in the air-cooled 911's.
The second issue is that the Motronic system's knock sensors reduce ignition timing as the heads get hotter due to incipient detonation increasing knock sensor activity. One can watch this process in real time with a scan tool (Bosch Hammer for '95's and either PST-2 or any generic OBD-II scan tools for the '96-'98 cars).
It REALLY pays dividends to keep a lid on oil (and thus) engine temperature to maintain best power, freedom from oil leaks, and best durability/longevity.
Higher octane fuels, do not "cure" the problem, they only give you some margin. I will say that 100 octane fuels are highly recommended for all these cars when participating in track events for all the reasons outlined above.
My 2 cents worth,.......
Good talking with you this afternoon,....
As we discussed, this is a somewhat complex issue as you were feeling the results of two different things.
Elevated outside air temperatures affect two things for air-cooled engines; they reduce volumetric efficiencies due to high cylinder head temps and lower the threshold of detonation. One doesn't see cylinder head temps, but you can watch oil temperatures and they lag behind head temps at all times.
When oil temps reach 210 deg F and above, engine power begins dropping and its not a linear relationship between oil temp and HP losses. its more logrimithic. Controlling engine temps is THE key for maintaining best performance (and longevity) in the air-cooled 911's.
The second issue is that the Motronic system's knock sensors reduce ignition timing as the heads get hotter due to incipient detonation increasing knock sensor activity. One can watch this process in real time with a scan tool (Bosch Hammer for '95's and either PST-2 or any generic OBD-II scan tools for the '96-'98 cars).
It REALLY pays dividends to keep a lid on oil (and thus) engine temperature to maintain best power, freedom from oil leaks, and best durability/longevity.
Higher octane fuels, do not "cure" the problem, they only give you some margin. I will say that 100 octane fuels are highly recommended for all these cars when participating in track events for all the reasons outlined above.
My 2 cents worth,.......
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Joined: Dec 2001
Posts: 1,414
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From: Redmond,Washington
Sometimes in traffic around here my temps would creep up and I installed the manual over ride switch for the oil cooler fan and have had no problems whatsoever since. Go to Robin's DIY site and follow the directions...very simple and effective. I don't feel I need an oil cooler as I can keep the temp on the first mark.
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Joined: May 2002
Posts: 8,138
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From: USVI
An extra oil cooler would be a complete waste of $$$ in your case and for most Porsches that don't live on a track. Mid-point on the oil gauge is well within the operating range of the 993 and temperature spikes upto 250F are not going to cause any problems. If the temperatures are staying put up there its another story and an extra cooler might be helpful but not for the 20 minute DE session. If you do actually drive around and compare cylinder head temperatures with oil temperature you'll see there isn't much correlation, the CHT varies between 255F-300F depending on how fast you are driving (and the RPM). You have to be running pretty close to redline all the time for the CHT to stay at 300F (meanwhile your oil temperature may have stabilized at 194F). If your car is sitting in traffic at idle the CHT will drop back down to 250F. I've also never noticed any correlation between the knock sensors triggering and CHT (stock chip & 93 octane fuel over several thousand miles since I bought a Bosch Hammer).
Last edited by JasonAndreas; May 30, 2005 at 11:08 PM.
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