2001 Montana cooling fans don't start

[va3rrw]

I have a 2001 Montana with 3.4L engine. The engine failed a week ago due to a blown head gasket (which seems to be a very popular problem with GM engines). Spent $1400 fixing it, now the cooling fans won't run.

Coolant Temp. gauge works fine
When A/C is on and compressor is running, the fan runs at low speed okay.
Unplug the wires from Engine Coolant Temperature sensor, the fan runs at high speed non-stop.
With A/C off and sensor wires on, idle the engine for a while, the temperature goes above half mark. Then drive the van on highway for a while, the temperature goes back to normal as before.
Opened two bleeders (one beside temp. sensor, another one at the left-front side of engine), no air/steam found.

Never see temperature goes above half mark before the engine broke down (except WHEN the engine broke, temperature hit red line)

The mechenic who fixed the gasket insist it's the PCM problem, which I don't believe.

Any suggestions or ideas would be greatly appreciated.

[GregA]

Hi & Welcome to the forum!

It sounds like the PCM is doing what it should when controlling the fans (LOW, HIGH, etc.).

I have a couple of pages on my site that might help, or at least give you more information about the fans and cooling cycle.

Montana/Venture Information

On that page you will find 3 links at the top of the table that relate to the cooling system.

After reviewing those pages, I would ask: "Have you let the temperature go above 220-230 degrees F?"

I ask because that is where my fans first turn ON, and then the temperature goes back down to about 200, when the fans turn back OFF.

I would also ask: "Was the thermostat replaced when the gaskets were done?" If so, it might be a different temperature thermostat from what you had before, giving you "different" gauge readings from what you are used to.

Let us know what you find.

Take Care & 73,

[va3rrw]

Originally Posted by GregA

It sounds like the PCM is doing what it should when controlling the fans (LOW, HIGH, etc.).

That's what I thought, except it seems can not start the fan when the coolant temperature is high.

Originally Posted by GregA

After reviewing those pages, I would ask: "Have you let the temperature go above 220-230 degrees F?"

No. I turned off the engine and unplugged the sensor wire (to make the fan run at high all the time) when I saw the temp. gauge went above half way.

I will drive the van with sensor on for a while to see if it will overheat.

Originally Posted by GregA

I would also ask: "Was the thermostat replaced when the gaskets were done?" If so, it might be a different temperature thermostat from what you had before, giving you "different" gauge readings from what you are used to.

The thermostat was not replaced, but the engine coolant temp. sensor was, I can see it's outside doesn't have the aging color as the rest of the engine do and is in black and clean.

I purchased a code reader today. Got one code: P0118 - Engine Coolant Temperature Circuit High Input, possibly due to my disconnecting of engine sensor wire. I then erased the code, because in another post in this forum one member mentioned he had to erase the code to make the fan works after changing a dead sensor. I then idle the engine for a while, temp. went to half way, the fans still don't work (it's cold outside here, -2C, about 28F).

I will also check out the link you provided.

Thanks a lot,

73s,
Ken

[va3rrw]

Originally Posted by GregA

After reviewing those pages, I would ask: "Have you let the temperature go above 220-230 degrees F?"

After reading your "Coolant Temperature Gauge" image, I would say the enginecoolant temp. is around 215 degrees F. I haven't let it hit the 226 mark yet.

[GregA]

Originally Posted by va3rrw

After reading your "Coolant Temperature Gauge" image, I would say the engine coolant temp. is around 215 degrees F. I haven't let it hit the 226 mark yet.

I would suggest that you TEST IT - just "let it run" and see WHEN the fans turn ON - You may be OK. If it gets OVER 230-240 and the fans don't come on, then I would say you have a problem. Then you could use the Defrost / AC setting to cool it down.

Take Care,

[va3rrw]

I will give it a try.

Thank you.

[blazes9395]

It sounds like the engine is not getting to the temperature needed to run the fans. If you have a scanner that is capable of showing you a live data stream, bring up the temp sensor reading, go for a drive and watch the temp reading the scanner is displaying. this reading is what the on board computer is using. When the temp gets to the correct range on the scanner display, go outside and watch for the fans to turn on. If they don't you know you have a problem. No need to guess, throw a scanner on, it will make your life much easier.

[va3rrw]

Originally Posted by blazes9395

It sounds like the engine is not getting to the temperature needed to run the fans.

blazes9395 is right. The fan start temperature is higher than what the thermostat is set to open. I have to wait until the temp. goes above half mark to see the fan kicks in at low speed, even though the temp. will be at one quarter mark during driving. This also matches GregA's chart on his website (thanks a lot, Greg).

As a comparison, my 01 Honda Accord always keep the temp. at the same level. When I stop at red light in normal weather, I can feel the fan kicks in after idle for 10-20 seconds.

I was over paniced. The cooling system is running fine.

Thanks a lot, Greg and Blazes9395.