Overheating

[Ashley Bowler]

…….I was just driving my 993 in blistering hot weather in heavy traffic. I was going 3-5mph on the 405 freeway when I noticed the temperature gauge rising to a dangerous level.

My question is, I know what happens when a water cooled engine overheats, but what happens to an air cooled Porsche? What are the first nasty signs? Does anything blow? Hoses, etc?

Thanks in advance.

[Bill Verburg]

Nver got mine hot enough to find out, sounds like you fan(s) are not working.

[Ashley Bowler]

Originally Posted by Bill Verburg

Nver got mine hot enough to find out, sounds like you fan(s) are not working.

That’s interesting. So if the fan(s) are working and everything else is in good shape, it’s virtually impossible to overheat an air-cooled engine? No matter how slow the traffic is or how hot the outside temperature is running?

I know that the A/C needs the car to be moving at speed to be effective. So I guess in stop & go traffic, it’s better to turn it off?

[Don Plumley]

Look at P-car.com regarding the fan resistor. Could be yours is not working at speed 1, but would kick in at a higher temp.

Once in stop and go traffic, I also noticed my temp creeping up - far higher than I see on the track. Consider the fan switch mod so you can turn your fan on manually.

You cooler could be caked in gunk - might be worth a look as well.

[Tom W]

In really bad traffic my temps would get to about 9-10 o'clock on the gauge. I installed an over-ride switch years ago and simply turn the fan on to high as soon as it gets to 9 o'clock. It works great. (My low speed fan was inoperable at one point because the ballast resistor was bad. Check the p-car.com DIY info to help trouble shoot.

[cjoenck]

First, yes, an "aircooled" engine can overheat. Actually the 964 and 993 are not strictly aircooled, they are oil / aircooled - hence the oil cooler in the front. Oil has a specific temperaturee range it works in and oil starts to age / break down fast when extremely hot, loosing some of it's core properties because the longer carbon chains (molecules) start to break down.

Second, get the manual override switch or install a different oil temperature sensor that activates the oil cooler fan at a lower temperaturee. There is a BMW part that fits the bill - our host knows the part number. Unfortunately, the standard oil cooler in a 964 or 993 is not in an ideal spot so if you run in stop-an-go traffic a lot, you might want to think about an additional air duct to the cooler.

There are no good early warning signs of an oil cooled engine overheating I can think of - but that just means I have not heard of them... Oil breaks down quickly outside the upper temperaturee limit for a given oil and you will hear metal grinding on metal and experience sudden engine death - granted, that is the most extreme outcome.

[kang]

First, what do you mean by a “dangerous” level? Where was the temp gauge? 9:00? 10:00? In the red?

I don’t think I’ve ever heard of a 993 with the temp gauge in the red, even sitting in traffic on a hot day.

Here are the DIY’s mentioned above:

Fan Operation and Troubleshooting: http://p-car.com/diy/fan/index.html

The manual override switch: http://p-car.com/diy/fanswitch/

[Ashley Bowler]

Originally Posted by kang

First, what do you mean by a “dangerous” level? Where was the temp gauge? 9:00? 10:00? In the red?

I don’t think I’ve ever heard of a 993 with the temp gauge in the red, even sitting in traffic on a hot day.

Here are the DIY’s mentioned above:

Fan Operation and Troubleshooting: http://p-car.com/diy/fan/index.html

The manual override switch: http://p-car.com/diy/fanswitch/

It was at the 10 o'clock range with these split second jumps into the red, which really freaked me out. Once the car was over the hill, and traffic lightened, the temperature went right back down.

If it is "gunk" on the cooler, is it something I can take care of? Thanks again, for the input.

[kang]

10:00, on a hot day while sitting in traffic, is not unusual at all. Especially since you said that once you picked up speed the temp went right back down again. That sounds very normal to me.

What do you mean by split second jumps into the red? Do you really mean the needle jumps into the red for just an instant and then goes back again? If you blinked, you’d miss the jump? How much time does the needle spend in the red? If it’s just a fraction of a second, I’d say there is something going on with the temp sender or the gauge, rather than your temp is really up in the red or there is gunk on your cooler.

If you had gunk on the oil cooler, the needle would stay in the red much longer, and the temp wouldn’t cool right back down again once you picked up speed, like you said.

[Ashley Bowler]

Kang,

The jumps into the red were probably along the 2-sec. range. it was enough for me to have fantasies of waiting for a tow truck by the side of the road, then thinking about an insane bill from my mechanic.

it also took me back to my college days of driving in ancient VW's that would seize and blow a piston.

[kang]

Even a two second jump makes me think that particular issue is with the temperature sensor/sender and/or the gauge. There’s no way the actual temperature spiked for two seconds and then returned to the previous level.

The 9:00 level is around 200 degrees, plus or minus. The red level is around 300 degrees, plus or minus. There is no way the actual temperature went from 200 to 300 and then returned 200 in two seconds.

[cjoenck]

Agree, this sounds like instrumentation. I would change the temperature sensor first. Easy DIY fix once you get to the part. Porsche part # is 911-606-112-00-M100 for approx $32.00 from our host.

Good luck.