About to give up TOO HOT (long)

cweatherington · 07-09-2002, 01:23 PM

I finally got all my cooling issues solved, or so I thought. The car runs perfect right at 1 to 1.5 on the temp gauge even in 98 degree 90% humidity weather (which we’ve had all week). It idles in the driveway and never breaks a sweat. I've replaced the temp sender, thermostat, and fan switch (all lower temp parts). Running it hard it has climbed to the 2nd bar but doesn't stay there long it cools back down when I let up on it. Long story short pretty confident in my cooling system.

NOW for the kicker. I turned my AC on Sat. and the temp kept climbing up to the 3rd bar when I turned the AC off. With it off the temp dropped back to normal. I've tested this multiple times and every time I run the AC the temp starts climbing. Its slow may take it 15 mins. to get to 3rd bar and about the same to cool back to normal, so don't think its just an electrical thing (like turning your lights on and the gauge rising a bar or something like that).

Call the mechanic whom I think is great and he said the radiator might be blocked.

My questions are:
1. What the heck does the AC have to do with engine temp?
2. Wouldn't a blocked radiator run hotter all the time?
3. Could a faulty compressor pull the engine down enough to overheat?
4. Any other ideas?

Sorry it’s so long I'm just REALLY frustrated and need to vent.

Thanks
Chris

ae1969 · 07-09-2002, 01:44 PM

1. What the heck does the AC have to do with engine temp?

If you have ever pulled a trailer with a truck up through the rockies and had your A/C on you will know what I mean.

2. Wouldn't a blocked radiator run hotter all the time?

Not necessarily..... you may be getting enough flow to keep temps down, but not enough under stress (but you do mention you have driven it hard)

3. Could a faulty compressor pull the engine down enough to overheat?

It can, but usually if its going you would know......bearings grinding....and the compressor actually not working would be the obvious sign....

4. Any other ideas?

The radiator idea is a logical one........

I replaced my radiator this year and it actually keeps the engine temp on the first line....it creeps up slightly with the A/C on.
Last year it was hovering around the 2nd line...... The radiator ranges from a low of $200 to $300 U.S

Considering you have replaced everything else this maybe it. I would assume you are still on the original rad?

You may try flushing the rad by itself a few times.... disconnect the hoses.....try a reverse flush on it .....who knows....you might dislodge enough crud to make it work a little better.

Good luck.

drew1 · 07-09-2002, 03:02 PM

see if both fans run when AC is on.

drew1

AFJuvat · 07-09-2002, 05:41 PM

Your mechanic is blowing a bit (actually a lot) of smoke. You have already proven the radiator is fine.

Mine does the same thing both with R-12 and R-134. I have noticed that it is a bit more pronounced that I converted to 134 - but nothing that would concern me temperature wise.

The only thing I can speculate as to the cause is:

1. Compressor getting good and hot, It probably doesn't help that my compressor isn't nearly as efficient as it used to be. The compressor forces the freon into a liquid, generating a lot of heat which leads to.....

2. All that hot liquid freon running through the condensor (sitting right next to the radiator), throwing quite a bit of heat leading to:

3. A good deal of hot air running through the radiator, reducing cooling efficiency until everything cools down.

I would make sure that your radiator and condensor are good and clean - I would also consider combing your the cooling fins on the condensor if they are bent from road debris.

As long as your fans (both) are running and the temp never goes above the 3/4 mark, I wouldn't worry too much. If you are like me, you check your coolant levels at least once a week anyways.

AFJuvat

cweatherington · 07-10-2002, 04:53 AM

To follow up. Yes both fans run when the AC is on. I ran it all the way home yesterday (about 20 miles) with the AC on. It climbed to the third mark but I let it run to see how hot it would get. It set right at the third mark from about 5 miles from my office all the way home. Never got about the 3rd mark. AFJuvat your # 3 is the exact reason the mechanic said it was radiator. Because it would work well enough to get by when there wasn't the extra hot air blowing through it. I think I'm going to let it go a week and see if it ever gets above the 3rd mark before I buy a radiator.

Is there anyway short of flushing to test a radiator?

Thanks
Chris

Lawrence Coppari · 07-10-2002, 08:16 AM

I assume your system is well bled?

ae1969 · 07-10-2002, 11:00 AM

No you can't test a radiator.....well you can but, testing thermal- dynamics and heat transfer requires a more complicated measuring device capable of duplicating almost any kind of driving condition as it relates to the flow and heat transfer of automotive coolant.

You have obviously tested everything. Temperature creep underload usually signals a radiator problem like your mechanic said.

Good luck.

gforces944 · 07-11-2002, 08:41 AM

When we say "the third line", we're talking about the one that marks the safe operating limit, right? not the one where a red light comes on when hit--at the top of the gauge, right?

If that's the case, then you should be safe. It's been hot here the past couple of days in the bay area, Cali., and my needle is usually where yours is at. If it exceeds that line, that's when you worry.

Flush your radiator like said. Have you ever mixed oil and coolant before by running the car with a blown head gasket, or oil-cooler gasket? or for any other reason that oil might get into coolant? If you have before, it might be a good time to drop your radiator and take it to a radiator shop to be cleaned out. It's good to do because they really clean it out better than any flush that you buy at Kragen or Pep Boys.

Also, if it isn't cost prohibitive, upgrade your radiator to the all aluminum one on http://www.************************. It also has more cooling fins per inch and supposedly has more cooling power than the original, which makes sense if you plan to modify in the future. The OG ones are a combo plastic/aluminum, and are more susceptible to failure than other radiators.

cweatherington · 07-15-2002, 04:46 AM

Well replaced the radiator this weekend, but as with all good Porsche's something else broke in the process.

The brand new CV/Axle that I bought went out on me this weekend so haven't been able to drive the car to find out the results of the new radiator. I can tell by looking at the old one I'm pretty sure it was stock original. So at the very least I didn't think it would hurt anything to replace it.

Thanks for all the help. I love this place. I'll post a follow-up when I get to drive it later this week and let you know weather it helped.

Chris