LT1 Cooling system issues (electric fans won’t come on)

[The Love Boat]

Hello all, does anybody know what actually “tells” the electric fans to come on? Is it the sensor that’s located in the water pump?

I have a 96 Buick Roadmaster with duel electric fans that will not come on automatically. If I pull the plug off of the water pump sensor they both come on with-in 15 seconds. I have checked the fan relays, the fuses and the draw on the fan motors (all seems to be fine). From what I have read on this site and others the system is working correctly if you remove the plug from the WP sensor and the fans start. So im suspecting the sensor in the water pump has gone bad…however before I swap it out I wanted to see if anyone here has another suggestion.

PS: I know these things are set to run up to 200 plus degrees before the fans come on…however if I left this car alone it would over heat without the fans kicking in. (And the car did not do this before). The fans use to kick in during stop and go traffic, however they aren’t anymore). Also no work has been done to the cooling system…its all OK and holds pressure.

Thank in advance for any info.

John

 

[Goldmaster]

The sensor in the pump is the one that controls the fans. It could have gone bad. But first, have you made sure there is no air trapped in the system? When I got my 95 winter beater, the fans wouldn't come on, and all I had to do was top off the coolant, and bleed the air out.

 

[Krzdimond]

In short, the sensor in the water pump tells the PCM what the temp is, and the PCM in turn tells the fans to come on.

 

[The Love Boat]

Thank you gentlemen, that’s what I suspected however its nice to have it confirmed by others here on the forum. GoldMaster…glad you’re OK, sorry about your winter car.

I truly appreciate the advice and info.

PS: No air in the system, I did burp it just to make sure. I suspect the WP sensor must have given up. The car has never given me any issues. Any tricks/info pertaining to the removal/installation of the WP sensor?

JP

 

[MrBuick (Magnum)]

Be quick when swapping the sensor. Get the new one taped up, and ready to go. Pull the old one, and quickly put the new one up there to stop the coolant flow.

Have you gone into the climate control to check the reading the Sensor is giving? I think it is -24, and is displayed in C*...

 

[The Love Boat]

Howdy Cory, no I have not...in fact I have never used it for anything other then adjusting the temp 🙂 If its not too painfull could you walk me through how you would go about checking it?

(Learn something new everyday on these cars).

JP

 

[MrBuick (Magnum)]

http://www.buickforums.com/forums/showthread.php?p=43614#post43614

I should prolly add this info to our sticky post.

EDIT: Added.

 

[The Love Boat]

UP DATE. Well I read all the posts on this site and on the other Forum and everything pointed to either air in the system or a bad sensor in the water pump. So I bled the system 8 times. I was 100% sure that the system was air free...still the fan would not kick in. I then changed the sensor in the WP. (Bled the system again 4 times). Guess what...no freaking fans! So I gave up and took the car to a local shop that "knows" LT1's. The shop owner asked me if my water temp gauge worked? and I said yes it did. I then told him all the steps that I had taken. He smiles at me and says its the sensor in the head. I of course reply that it can't be as it has nothing to do with turning the fans on. Well to make a long story short, they order the part and install it. They start the car up and let it get to temp. The gauge gets to the 3/4 mark and the fan kicks on! the gauge quickly drops to the half way mark. Problem solved.

Im not sure how this has anything to do with the PCM getting temp info...however clearly in my case it was the missing link. I hope this helps others with the same problem.

John

 

[Goldmaster]

Hmm, had to of just been a coincidence in my opinion. As you already knew correctly, the one in the head has nothing at all to do with commanding the fans to come on. Was the temp guage working before you replaced the sensor in the head?

 

[The Love Boat]

Hello Goldmaster, To say Im dumbfounded would be an understatement. From all that I know about these cars the sensor in the head purely feeds the guage on the dash. To answer you question yes the gauge did work before the sensor was changed. All I can say is that the car is working 100% now. Im happy to have my fans working again, however I would love to know why the fans did not work before the sensor was changed. (From what I have seen on line, lots of B-Car owners have had or are having the same issue(s) with thier fans.

JP