Car runs too hot

[CreepyOldGuy]

New guy here. A little history of my car before I ask my questions; I purchased a 94' AWD MT wagon last fall to use as my winter commuter. The car had a little over 200k miles on it at purchase, I put another 25k on it through the winter months - with no problems, the only thing I have done is change the oil and purchase winter tires. I bought the car from a small dealer, they claimed the previous owner had recently replaced the timing belt and radiator. I can't say for sure on the belt, but the radiator is definitely a newer aftermarket unit. Looks like they did the hoses at he same time.

Now that it has quit snowing, I'm not driving the car much, but I have ran across a cooling issue with it. When I pull a long grade at higher altitude, idle for awhile, or sit it in traffic, the car heats up. I did figure out a couple of things but I'm not sure where to go with them. The cooling fans do not come on when the motor gets warmer. I can force the fan on the driver side to come on by turning the AC on, I have managed to keep the car somewhat cool by switching the AC on when the car starts to heat up. Obviously this is not good. How do I trouble shoot the inop passenger side fan and the fans not coming on without AC? What else could cause my overheating issues? I can understand the car heating up at idle or in heavy,slow traffic if the cooling fans are not functioning, but it seems to me that at higher speeds, pulling a grade, I should have plenty of air flow to keep things happy even without the fans?

Thanks for the help!

[robertpaige]

Check the fan fuse, which is located in the fusebox, which is to the left of the driver side foot column. Right where your left foot would rest.

Maybe try burping your coolant system, and see it that helps.

[Legacy777]

Welcome to the BBS.

The first thing I would probably suggest doing is probably replacing the coolant temp sensor. It is the larger of the two sensors in the coolant crossover pipe under the intake manifold on the passenger side. It plays a big role in controlling the ECU's fuel enrichment as well as the fans. Even if it's not "bad", it's probably a good idea to replace it with the mileage that is on the car. They're about $20 at some of the online subaru dealerships, http://www.subarugenuineparts.com http://www.subaruparts.com http://www.1stsubaruparts.com

You can look through these pics where I've labeled the different parts under the intake manifold, including the coolant temp sensor, http://www.main.experiencetherave.com/s ... /injectors

The second thing I'd suggest checking is looking at the thermostat. Subaru uses a taller/deeper thermostat that goes into the water pump housing. The aftermarket t-stats can create random cooling issues. There are bunch of pictures of the subaru t-stat in the middle of this page of pics

http://www.main.experiencetherave.com/s ... age_02.htm

I'd start with those two things first. Since the fans work with the AC, I would make the assumption that the relays work and the problem is more in the fan control, i.e. ECU.

I guess to clarify, do both fans turn on when you turn the AC on or just one?

[CreepyOldGuy]

Hey guys, thanks for the great feedback! It is much appreciated.

Legaccy777 - the driver side fan comes on only with the AC. Passenger side does not turn on at all. Does this still point to the coolant temp senor? I will replace the temp sensor and the t-stat, sounds like a good thing to do on a 225k mile car.

[Legacy777]

There is a jumper connector that is suppose to link both fans together. The driver's side fan is supposed to come on via the ECU and is temperature dependant. The passenger side fan is tied to the HVAC/AC system. However, there is a jumper that ties both fans together. It's around the passenger headlight area.

Since the driver's fan comes on with the HVAC, I'm guessing that jumper is working properly and either the motor for the passenger fan is dead or something is up with the wiring.

I'd start with the t-stat & coolant temp sensor and then go from there.

[CreepyOldGuy]

I ordered a temp switch and t-stat today. Will install them when they arrive.

Regarding the fans, any interchangeability between later years? I was at the local self serve junk yard today, they have a bunch of 95+ Subies, I'm sure I could find a good used fan for cheap.

[Legacy777]

The motors may be interchangable. Look at how they bolt to the fan shrowd and the electrical connector.

[CreepyOldGuy]

I finally had a chance to work on my car - I replaced the thermostat and temp sensor, flushed and replaced the coolant. Car still runs hot pulling grades. Still runs hot idling in traffic but I believe this to be the fault of the inop passenger side cooling fan as when I turn the AC on and slide the temp to hot so the compressor does not cycle, driver side fan comes on, car cools down - slowly.

I know I need to figure out why the passenger side fan does not work as I believe that is the problem with my overheating in traffic. But the high temps at highway speeds have me baffled. I thought this was usually signs of a inadequate cooling system? Any more thoughts on where to go with this? Thanks!

[mike-tracy]

You used a factory thermostat, right? Also, I had similar issues a while back - and it turned out the 'other' coolant temperature sensor was faulty. The one that sends a signal to the dash. Replaced that and the gauge stayed in the normal range.

Being that you're in Colorado, can you find a junkyard fan locally?

[Legacy777]

You used a factory thermostat, right?

This is very critical.....you must use a factory thermostat. Stant does make an aftermarket one that supposedly works like the factory one, but I have not used it.

[CreepyOldGuy]

Yes, I used a factory t-stat. The one I pulled was aftermarket, I was really hoping I had found my problem.

Lots of Subie's at the local pull and play places around Denver. I could easily grab parts. From the consistency of my heating up problem, I think the gauge functions correctly. If it or the sensor were bad I would think I would get more erratic readings, or at least at other times besides pulling grades and in traffic?

[CreepyOldGuy]

Going to grab a junkyard fan on my lunch break tomorrow and see if that helps.

[Legacy777]

The gauge temp sensor is probably fine. The ECU coolant temp sensor is the more critical one and what triggers the fan to turn on. The ECU is pretty dumb and may not trigger a code even if the sensor is bad.

[CreepyOldGuy]

The gauge temp sensor is probably fine. The ECU coolant temp sensor is the more critical one and what triggers the fan to turn on. The ECU is pretty dumb and may not trigger a code even if the sensor is bad.

I replaced the ECU temp sensor, still no passenger side fan. I picked up a junkyard fan, I will test and install it this weekend and see what happens.

[mike-tracy]

I agree that the gauge fan sensor is prob fine.

Mine would creep up and down with the accelerator pedal, and would drop from half to 1/4 on hard acceleration! In traffic it would slowly creep up to just below the "hot" line. I changed the sensor and nothing else (I had a known good water pump and brand new oem t-stat in there from earlier), and the gauge hasn't ever gone above half way since. neither fan would come on unless I hit the defrost button, leading me to believe it was the sensor.