Ok guys. problem with a buddies car. 94 V6 3.4. runs hot, no fans comming on. I know this topic has been covered however, the problem isn't addressed as the posters go off on tangents and get off topic. So the relay is fine, the fusable link is fine, I jumped the relay area in the fuse box and they come on, I was going to keep the jump inplace for now but the fans stay on with no keys in. Also, what is the best method of purging the cooling system for this car? I read something about the A/C relay, what was that about? I need some clarification on that. Another thing, the car only took 1 gallon (should have taken 3, or 12 qt) of fluid into the radiator (done by the owner) and it seems toped off, I squezed the hoses and the fluid rises to the rad cap, when the car is running the fluid comes out of the overflow hose. Water pump was recently changed by the owner as well. It has a 180 thermostat.

 

easiest way I found on mine was to pull the temp sensor in the Dr. side head then you should be able to fill it almost all the way. pour slow and have somebody watch the hole so you can put the sensor back in when it starts running out. then top off the rad. and wait about 5 or 10 minutes for it to settle, top off again, and let it warm up. should be close enough to open the thermostat and activate the fans. let it cool down again and the top it off and you should be ok. if theres not enough coolant in the system the sensors cant tell the fans to come on... may just need to pull that sensor so it'll bleed and you shouldnt have any other problems. --- also, that sensor is for your gauge on the dash, the one for the computer/fans is up by the thermostat on the intake.

 

Refill capacity:
I suspect your friend just drained the radiator instead of draining both the radiator and engine block, The radiator only holds about half of the total coolant, so when it was refilled it only took whatever the radiator could hold.
Fan not going on:
From the test you done it proves the power from the battery is getting to the relay contacts and that the fans are OK but says nothing about the control power to the fan relay windings, the relay itself, or if the relay sees a signal from the PCM. A quick way to test the whole system is to disconnect the wires from the ECT sensor (Engine Coolant Temp Sensor not the temp gage sensor, they are two different things). Put a jumper (resistor)between the two wires (YEL & BLK/PNK) going back to the PCM (use a 100 to 200 Ohm 1/4 or 1/2Wattresitor, from Radio Shack, to protct the PCM). This will simulate max coolant temp and the PCM will request the fan to operate. If the fan operates you probably have a bad sensor or the coolant is not getting to the sensor. If the fan does not come on, you probably have some wiring/connector problem somewhere from the sensor to the PCM, or from the PCM to the fan relay.
If you have a scan tool you cam monitor the coolant temp and PCM reaction as youjumper the leads, if it shows hot you are good to the PCM and the PCM is seeing the high temp. If the PCM is working as it should,it will send a fan ON request (ground to the fan relay control lead).

 

Exactly what I suspected. I will have him by this weekend again and do an entire flush. I am suspecting the PCM. We pulled the relay from the box and hooked it to the fog light relay and they came on - telling me the relay is good. The sensor on the drivers side of the motor , near the spark plug/exhaust manifold was recently replaced. I will do the 'disconect wires and jump yel /blck' technique and see how that goes. I am more used to older type motors where, if you had a heating problem you just threw the thermostat out and be done with it. I would do that here but I am afraid I will make more problems. Thanks for the advise. I will keep you posted.

 

So just curious Pete -- are you saying if you do a flush with the Prestone flush kit that you are still not doing a full flush -- i.e. you need to also release some drain plugs on the block too? Please clarify...

 

A power flusher will probably suck all the old stuff out, but the ones for the DIY although they clean the whole system out,do not empty out the water jacket. The only way to get the water out without some kind of a pump is to open the plugs on the side of the block. In some cases the Knock Sensor also act as a plug. Theplugs are usually hard to get to, and rusted in place. It really does not matter that much as long as you remember to use straight antifreeze when you fill the radiator, because there is about as much straight water left in the block to dilute it.

 

That reminds me, Pete, about the tester I made a few weeks ago. It's a really versatily GM tool.

I went to RadioShack and bought a 5k Ohm potentiometer, a good length of 18g wire, a project box, and got my hands on a few small cotter pins. By using an ohmmeter, I was able to tell which terminals on the pot. were paired and then soldered about 2 1/2 feet of wire on each terminal and shrink wapped the joints. Then, I took the cotter pin and broke the two long end pieces off and soldered each to the end of the wires from the pot. After shrink wrapping those joints, leaving 3/4 inch of the pins exposed, I drilled a hole in the project box and inserted the **** of the pot, secured it, and labelled the twisting directions either + resistance or - resistance. Now I have a fully functional GM potentionmeter tester (Coolant sensor, throttle position sensor, fuel level gauge, etc.). By inserting the two pins into the corresponding sockets in the PCM side of a sensor, I can give the PCM false readings. I was able to cold start my car and immediately turn the resistance down, forcing my high fans on. I then used a GM Tech 2 scan tool to measure the range of my tester. It ranges from 59 to 284F. A 10k potentiometer will allow it to read lower.

I'd recommend anyone make this simple, inexpensive tool. For $13 materials, I have a tool I can use time and time again for any GM vehicle that may roll into my bay.

 

That is an excellent idea, really makes checking sensors out a lot easier. I think I am going to put one together this weekend.

 

Just an update. This thing is making me sad. Replaced the fan motor, relay is good, all fluids flushed to include the heater and all lines, associated sensors replaced and all wires were cleaned. Monday I will try to install the new computer.

 

Also, check your thermostat. If it's stuck closed it won't let the hot coolant (oxymoron?) reach the temp sending switch which tells the fan to turn on. I know from experience this can happen. It's one of those simple problems often over looked.