Stock temperature for the electric fan turn on.

Mechanicboy

Dedicated LVC Member
Joined
Nov 18, 2009
Messages
1,407
Reaction score
3
Location
Durham
At first I thought I had a blown head gasket because a 1996 mark I bought was losing coolant and would start to overheat right after I bought it. In diagnosing I noticed that if I let it idle it will start to continuously bubble out the degas tank around 204* coolant temp according to the computer and that the fan wasn't turning on. I should point out that there was no noticeable coolant smell so i believe it to be 100% water in the cooling system. I know that fan works because if I turn on the a/c it comes on. So I experimented and found that if I leave the a/c on while it's warming up the coolant temps stay below 190* and the coolant never bubbles out.

Now my question is what temperature is the fan supposed to come on and do you guys agree that it's most likely just water boiling and not a blown head gasket?
 
With my old engine i would start to get bubbles from the crossover long before the engine was hot enough to boil water. The cooling fan doesn't switch on till 215 degrees so running water is a bad idea. I would replace the water with coolant and retest. At that temperature there were probably spots inside the block hot enough to boil water.
 
With my old engine i would start to get bubbles from the crossover long before the engine was hot enough to boil water. The cooling fan doesn't switch on till 215 degrees so running water is a bad idea. I would replace the water with coolant and retest. At that temperature there were probably spots inside the block hot enough to boil water.

Thank you. Makes sense, probably boiling near the exhaust ports.
 
Straight water is fine. Coolant will increase the boiling point about 12 degrees max.

Boiling point of water is 212.
With antifreeze mix its about 224 @ 50% and 234 degrees at 70% mix.

But they system is pressurized, so with that in mind you should be able to reach about 270ish before boiling occurs. If you are boiling before that, the system is not pressurizing properly or its not flowing correctly and there are major hot spots.
 
Straight water is fine. Coolant will increase the boiling point about 12 degrees max.

Boiling point of water is 212.
With antifreeze mix its about 224 @ 50% and 234 degrees at 70% mix.

But they system is pressurized, so with that in mind you should be able to reach about 270ish before boiling occurs. If you are boiling before that, the system is not pressurizing properly or its not flowing correctly and there are major hot spots.

The cap is off the system when i'm testing this so i can add water and see if bubbles are coming out. What else would cause the system to bubble only when you're not using the a/c (forcing the cooling fan to come on). When I removed the plug on the crossover tube I noticed it seemed pretty rustic, maybe I need to change the o-ring there while I'm working on the system.
 
Are you sure your temp sensor switch (for the fan) just isn't bad?

Maybe I'm not understanding what your issue is but it seems like your saying the fan isn't coming on.....but comes on when the AC is on.

Start your car and unplug the sensor on the left (passenger) side of the crossover tube. Your fan should instantly kick on high. If it does, but won't when the car hits the temp.....that sensor is bad.
 
I was looking at my tune file today and if I remember correctly the fan is set to come on at 190.
 
Are you sure your temp sensor switch (for the fan) just isn't bad?

Maybe I'm not understanding what your issue is but it seems like your saying the fan isn't coming on.....but comes on when the AC is on.

Start your car and unplug the sensor on the left (passenger) side of the crossover tube. Your fan should instantly kick on high. If it does, but won't when the car hits the temp.....that sensor is bad.

No, I'm not sure that the sensor is good.

Yes I am saying that the fan comes on when I turn the a/c on but I haven't had it come on otherwise.

I'll check that out, thanks!
 
I was looking at my tune file today and if I remember correctly the fan is set to come on at 190.

Your custom tune or stock tune? I'm going off the OBDII port for my temperatures so if it's 190 then the switch is definitely bad.
 
No, I'm not sure that the sensor is good.

Yes I am saying that the fan comes on when I turn the a/c on but I haven't had it come on otherwise.

I'll check that out, thanks!

Hey no problem man! Sometimes you get lucky and it's a simple fix. I would think, judging by your issue, that your sensor is just bad and the fan isn't kicking on causing the car to overheat.
 

Members online

Back
Top