Cooling fans not working?

R

ralowth

New member
Joined
Apr 21, 2011
Messages
7
Reaction score
0
Points
0
Location
Ohio
Hello all,

I have a 1999 Pontiac Montana, that is currently saying its overheating, after many weeks of replacing things and searching we finally figured out that my fans are not always turning on. Some days they wont even turn on at all, we are almost 100% sure that this is the soul problem now, we have replaced the relays and it still has not helped the problem, I was wondering if anyone knew how to run a switch to bypass the relays into the inside so I would be able to turn on the fans manually?
:confused:

Please help asap!!
 
Are you 100% sure the rad is full and the cooling system is pressurized when the van is at running temp?? Also, did you replace the thermostat? Putting a manual fan switch won`t help if the above 2 things aren`t checked.

Ian
 
Yes we have done everything else, when we flushed the system our selves, the first time the fans turned on and then the second time the fans didn't turn on when we were flushing the chemical cleaner out, and the car start to over heat, we could see that the fans weren't on after it raised past normal operating temp and did not turn on at all close to max before we shut it off.
 
Fans turn on at aprx.225f. The ECM controls the fan through a relay. If you honestly believe the fans are not operating correctly then you eith have an ECM problem or a ECM to relay circuit problem.
You more than likely have a small headgasket leak causing the overheating. As far as overheating while flushing, that happens all the time when you get an air pocket in the cooling system.
______________________________
 
planenut_2000 said:
Fans turn on at aprx.225f. The ECM controls the fan through a relay. If you honestly believe the fans are not operating correctly then you eith have an ECM problem or a ECM to relay circuit problem.
You more than likely have a small headgasket leak causing the overheating. As far as overheating while flushing, that happens all the time when you get an air pocket in the cooling system.
Click to expand...

The fans are not even turning on when the ac is on. atleast they didnt the other day, it does not always overheat only randomly but its getting more frequently.
 
So to clarify (I love being clear!): You have replaced the mechanical thermostat under the throttle body with a NEW one, you have put a NEW coolant temperature sensor in the thermostat housing, you have replaced the rad cap with a NEW one, you replaced both fan relays in the fuse box under the hood with NEW ones, and you`ve completely bled the system of air using a proven method...not just assuming since the rad is full, that there are no air pockets. I`ve described in another thread how to do this.

Lastly, though VERY rare, the impeller on the coolant pump CAN break free from the pump shaft and not circulate the coolant.

You said that the fans don`t come on with the A/C? Does the compressor kick in for sure when you turn the A/C on???

If so, then it`s definitely an electrical issue that need to be fixed before you ruin your motor.

Ian
 
ianmcdca said:
So to clarify (I love being clear!): You have replaced the mechanical thermostat under the throttle body with a NEW one, you have put a NEW coolant temperature sensor in the thermostat housing, you have replaced the rad cap with a NEW one, you replaced both fan relays in the fuse box under the hood with NEW ones, and you`ve completely bled the system of air using a proven method...not just assuming since the rad is full, that there are no air pockets. I`ve described in another thread how to do this.

Lastly, though VERY rare, the impeller on the coolant pump CAN break free from the pump shaft and not circulate the coolant.

You said that the fans don`t come on with the A/C? Does the compressor kick in for sure when you turn the A/C on???

If so, then it`s definitely an electrical issue that need to be fixed before you ruin your motor.

Ian
Click to expand...

The A/C never worked as long as I have had the car ( a little over a year) Yes we have replaced everything else and there are no air pockets, the fans are not turning on when they are suppose to all the time, its not every time the van runs just every once and a while, but like I said before it is getting more frequent... The van has not been driven since the overheating problem has become more frequent. We noticed the fans when we where flushing the system.
 
ianmcdca said:
Lastly, though VERY rare, the impeller on the coolant pump CAN break free from the pump shaft and not circulate the coolant.
Click to expand...


i have no idea what you mean by this, I do know a little about cars but not very much my man knows more and has done all the stuff.
______________________________
 
The a/c compressor will not kick in if the system is depleted of refrigerant...so no fans will come on either if the a/c is switched on.

The impeller is what circulates the coolant. It`s attached to the inside of the pump. It`s VERY rare that it would come off, so I don`t think it`s your problem.

I`d be wanting someone to check the electrical to the fans. It can be done with a simple volt meter, but it`s probably better to leave this to a qualified technician...sorry. Wish it were an easier fix. You`ve done everything I would do.

Lastly, if you are driving the van at 40mph, will the van still overheat? Usually it shouldn`t. If it does, then, something is wrong with the cooling system not necessarilly the electrical. But, if it doesn't overheat while driving, the system is not to blame...it`s an electrical issue to the fans.
 
The vehicle DOES NOT overheat while driving at a constant speed, just in stop-and-go traffic. When the fans turn on, the vehicle IMMEDIATELY cools off, so when air is going into the engine it cools itself off. When I first turn the engine on, it takes about 20 minutes of idling for it to get to the red-line overheat area. If the fan comes on, it will cool off tremendously, leading me to believe that the problem is simply no air getting to the engine.

Any ideas how to safely wire a switch or some contraption to make the fans turn on manually? Also, that would be a good way to test the fans and see whether or not they are even good themselves anymore.

EDIT: Also, SOMETIMES the fans will turn on when I turn the A/C on, but that is also sporadic. I tried the "disconnect the coolant temp sensor" trick I read to get the fans to turn on, that didn't work.
 
Last edited:
ralowth said:
I tried the "disconnect the coolant temp sensor" trick I read to get the fans to turn on, that didn't work.
Click to expand...
I think you have to ground out the sensor then the fans should come on if that is the case you can add your switch in there .
 
You would add a switch connected to the Coolant Temp Sensor on the Thermostat-Housing? If so, how?

I was led to believe it would be done by the relays/fuses area in the engine.
______________________________
 
well if you ground the sensor and the fans come,and you test this many times and fill comfortable that this has bypassed your problems then you could add a switch in between the sensor and ground. One side of the switch goes to the sensor wire and the other side of the switch goes to ground.I think but not sure the sensor is an input to the computer(ecu) then the computer tells what relay's to come on .Again not sure how the sequence of operation is but if you can get the fans to come on by grounding out the sensor wire then you can make a switch do the same.
 
I have an idea! Whay not just fix it the correct way instead of Putting switches here or there!
The coolant temp sensor sends a resistance reading to the ECM. The ECM has the logic programmed into to decide if the resistance reading it's getting requires the coolant fans to be running. The ECM then completes the ground circuit for the coolant fan relay primary circuit, which in turn completes the power circuit direct to the coolant fans. Fans should run if the ground side of that circuit is good.
If you disconnect the coolant temp sensor, the ECM see temp as -37 it will not turn on the fan, and it will run rich. If you ground the coolant temp sensor the ECM will change the fuel also.
Here's the wiring diagram
http://i424.photobucket.com/albums/pp326/planenut_2000/diagram.jpg
 
Exact Same Issue

I have a '99 Pontiac Montana with approx. 167,000 miles. I also have the exact same problem, along with about a million more of the oh so stereotypical Montana problems.

Possibly, I have narrowed the problem down to a bad connection. There is a single wiring harness that comes from the top of the radiator, runs down the fan shroud, between the two fans, then at the bottom of the shroud, splits off to feed the two fans. The connector that I suspect is the large connector near the top of the radiator.

Here a week or so ago, I wiggled and pulled on that connector, and the fans went back to working, for a few days. After a while, they started failing again, at increasing frequency. So, I took the connector apart. I expected to find dirt, moisture, corrosion, damage, something. I found nothing. But, since reconnecting it, the fans have worked flawlessly.

Now, this may all be coincidence. For those of us that own these vans, we know how fickle and frustrating they are. It it turns out to not be the connector or near by wiring, then the next step is either some kind of interlock with the A/C or the PCT (Powertrain Control Module). I don't have access to the fancy computer tool to perform all the testing. My A/C doesn't work because of a major leak. Most likely, since most other Montana's suffer the same problem, it is a crack in the condenser. I have verified that I can get a replacement PCT from a local parts store for $380. They even have it in stock.
 
I think i know the issue i fixed my mother inlaw montero with the same issues but only one fan wasnt working if u want to check it before doing thiis you could try checking it with a volt meter first turn on your truck and the a/c check to see if there is electricity going to the fans before and after the connection that is on the radiator now if there isnt any take out one of the fans relay and check if there is power on the fuse box where the relay was there should be two of the holes with power you could also just slowly put the relay in and if it clicks its passing power to the fans the issue now is going to be from the relay to the fans.

That was the issue with my inlaw truck in the back of the fuse box i opened the back and some cables were stretched a lot .just enough that it could losen the connection between the relay tip and the fan cable. this trucks when replacing the battery you have to move the fusebox up and down alot and since almost all cables are too tightly i figured they would get lose so what i did was holding the cable and pushing it in from the back then i just aded glue with my glue gun waited till it dried and thats it connection was good again fans were working. Make sure you check the temperature when testing your truck and also if you dont know how a relay works google it its easy and most relays have a diagram ofwhat pins are what.
______________________________
 
I have a 2003 Montana 3.4L(150,000kms) which has the exact same problem and it only started this spring. When I'm on the highway its good to go and the temp needle stays at 1/3 or close to. A couple of lights and its fine. If I'm stopped at too many lights, for too long, the temperature shoots up to the three quarter mark. Its never went into the red but the temperature has not been over 15 degrees celsius to force it to that level. Last night I started my van and let it idle for 15 minutes but not once did the fan trip. Temperature guage got to the half way point. The funny part was I thought I could hear the sound(clicking) of the relay tripping but not once did the fan acitivate.

I tried turning on the AC and I had the same issue in that neither fan would activate. That being said my AC only works intermitently. Some days it works other it does not and it only blows the outside air in.

Other issues that may or may not be related

Heat in the winter is warm at best until the vehicle has been running for a half hour or more at which point it will start blowing out hot air.

The cooling system is full of fluid as both the overflow and rad were full. In fact the level is the same as it was last year when I had my block heater changed. Therefore it does not appear I'm losing any coolant and further to that there has been no white smoke to suggest there is a head gasket issue either.

I have not changed anything on my vehicle as I hate throwing money on parts if I don't know what the problem is. Its heading into a shop in a couple weeks for tire replacement and an oil change. When it goes in I will have them check out overheating issue with a strong emphasis on the cooling fans.

Keep us posted if you find the answer to this problem as it appears fairly common
 
Last edited:
Check for 12v at the fan when the temp is hot and you hear the relay click. Or check when ac is turned on. If u have 12v the bad fan if not work backwards .
 
You must log in or register to reply here.

Share this page

Back
Top