Overheating PT!

[mikedb]

Hi everyone,

I am having trouble with a '01 PT- it overheats when driving slowly at idle. From searching the forums, this sounds like a fan issue.

However, when I turn on the AC, I can hear the fan kick into low, and into high speed for short bursts. Today, with the engine temp over halfway on the gauge (starting to overheat), i turned on the AC. I heard a squeak from the engine compartment, and the fan came to life (into low and high speed), and the car cooled back down to half way.

To me this seems like an indication that the high speed side of the fan is starting, but not completely, to die. Is it possible that once the AC makes the fan spin on low, the high speed than works?

I have checked and exchanged my high speed fan relay with the horn relay, to no avail.

Today, while doing some highway driving, I hit some more traffic. As the car began to overheat, I turned the AC on, and the car cooled back down. AC off, and it started to overheat again. Keeping the AC on, the temps stabilized at a safe temp for 15-20 mins, until the traffic ended.

Sorry for the long post, but does this indicate a bad fan to you guys? Coolant level is fine, with no bubbles while the engine is running. Replaced the radiator cap today. No coolant in oil, no smoke/smell in exhaust.

Thanks for your help!
-Mike

[CREWZIN]

Sounds to me like maybe the coolant temperature sensor might be on the blink. If it's not registering that the coolant has reached a particular temp, it won't send a signal to the computer to turn on the fan by use of the relay. You already checked the relay and it the fan comes on with the A/C on, as it should, so either the sensor insn't working or you may have a bad ECM (the sensor is a lot cheaper).

[mikedb]

hey crewzin, thanks for the quick reply!

The coolant temperature sensor is an interesting thought- didnt even think of that.

One curiosity. In the repair manual it states

The PCI uses ECT sensor input to send messages over the PCI bus for temperature gauge operation.

This indicates to me that the sensor is also used for the coolant temperature gauge. So far, it seems to be very accurate- when the temp is over halfway, coolant is released from the radiator cap.

Given that my temperature indicator still works, do you think that the sensor is still the culprit?

Thanks!
-Mike

[CREWZIN]

That sounds reasonable and if it is, there's not many choices left other than the ECM.

[mikedb]

hey again!

Thanks for your help, I think that I at least know all the possible sources of the problem, which is a huge help.

I plan of action for now is to drive it 6 hours to my house (it is here at my girlfriends house right now, and I have no tools), and if it makes that drive, I will try to apply 12V to the low and high side of the fan. If the fan checks out ok, I will either short the fan across the relay posts to keep it on, or put a toggle switch across the relay posts, and control it from the cabin.

Is this a reasonable plan? I really don't have the money to be dumping into this (i doubt the car is worth $1000), and it's only use anymore is a 6 hour drive, back and forth, on the highway. Could leaving the fan on 100% of the time do any damage?

Thanks again!
Mike

[mikedb]

also, one other thing.

It seems from reading around here that the fan should always be on low while the AC is on. However, my manual does not necessarily state that (see below). What is the correct answer? It seems to me that since my fan seems to only turn on with the AC, that there is indeed something effy with my PCM.

Thanks!

[CREWZIN]

Yea, you can do that. I'd put a toggle switch in somewhere as even the PT computer shuts off the fan at above 35mph. It's not needed because of the air flow into the radiator at that speed.

When my fan motor died, I drove 90 miles from Orlando (using the expressway) back to my house and timed it so I wouldn't have to stop very long at any lights. Made it home with no problem.

I was typing the same time you added your question. As far as I know, the fan should run when the A/C in on. I've proved that to myself a couple times by starting the car without A/C and seeing no fan, then turning ON the A/C and seeing the fan switch ON.

[mikedb]

hey again,

So, I am here with the car again for the last time. I have put 12v across the fan connection, and the low speed side of the fan is definitely dead. It seems a little odd that the car will overheat even with a working high speed fan?

By pulling the low speed fan relay, the check engine light goes on, and the PT turns the high speed fan on full time.

Is this a safe way to drive for a while, until I can get the car home to replace the fan? My tools are 6 hours away from here, and the only fan motor close to me is $130. If possible, I would like to wait.

I am off to go for a test run. Thanks for you help!

-Mike

[mikedb]

gtook it for a drive, and things look good. The thermostat is controlling the temperature.

If there are no reasons why this is a bad idea, I think I will leave it for a few weeks.

Thanks for your help!
Mike

[CREWZIN]

Your welcome. Hope it works out for you.