I posted in the 'New to the forum' section first. I'm helping my neighbor diagnose his overheating problem. The truck has about 64k on it, he's replaced the thermostat thinking that would fix it. I showed him where the air bleed was, he said it had no air. I noticed the fan clutch had some play in it, not a lot, but enough that it made me doubt it, he replaced it, but it's overheated twice since then. If he gets out onto the highway and goes to pass someone, that's when it gets hot. He said he didn't think the water pump was flowing enough. It doesn't make a noise and the belt doesn't look like it's slipping, the tension felt fine., I don't know what the inside of the pump looks like, I guess the impeller could have come off if it's pressed onto the shaft.

Any ideas?

Larry Hampton

(editted)

 

Did he put the thermostat in the right way ? ..... A common problem would be the coolant temp sensor..... if I had to guess that's what it would be.

 

No, I should have been more specific, I'll edit, he changed the thermostat because he thought it was bad causing the overheating. What does the coolant temp sensor do? It doesn't have an electric fan, it's clutch driven. The gauge shows fine, then climbs and it loses power. I'm guessing the gauge and sending unit are fine. I don't think he's getting a code, I need to double check that.

 

If he replaced a bad thermostat with a good one that he put in backwards, it would still overheat.......... the coolant temp sensor isavariable resistance thermistor that changes resistance as the engine's coolant temperature changes. The sensor's output is monitored by the engine computer to regulate various ignition, fuel and emission control functions, and to turn the radiator-cooling fan on and off as needed........basically ...... if it goes bad you will overheat, have eradic temp's showing on the gauge, and the radiator fan willsometimesrun constantly.

 

I'll double check the thermostat, but the radiator fan is mechanically driven, driven off a belt with a clutch. It doesn't have an electric fan, so it can't be turned on and off. I would tend to think the coolant temp sensor is fine as when it gets hot, it's affecting timing and fuel.

I'm sorry for the bold, italic text above, but both times I posted prior, I talked about the fan clutch, I'm just not sure if you noticed it or not.

Do you know how I can test the temp sensor with a multimeter? His brother-in-law replaced the thermostat in it, he's a mechanic so we're guessing he did it right.

 

To be honest with you I'm not sure how that works..... if it is belt driven , what causes the cluth to engage/disengage the fan ?Does it have a temperature sensitive spring inside of the clutch ? ..... Testing the coolant temp sensor's ohms would be the way to check it ... but I can't seem to find the numbers on all data..... I'll ask one of the master tech's when they walk by.

I have sold 17 of those coolant temp sensors in the last 3 months.... just to give you an idea of whyI would guess that.

 

Most clutches are fluid filled (oil), they will spin with some resistance when the car is not running. (I believe this is the way it works) As you get up to speed on the highway, the fan doesn't have to do as much work as the air is coming thru the radiator, so it freewheels, to an extent. I believe the oil is spun out centrifically but the inner hub that is attached to the water pump shaft.

Not knowing what the water pump looks like, is it possible for something to be wrong in there that wouldn't cause it to weep or make noise?

 

I had a chevy that did the same thing. Changed the thermostat, checked the sensors the whole thing and couldn't find the problem. Talked to my dad and asked if I washed out the radiator. I said "you mean flush it?" and he responded "no, clean out the fins". I took a hose to the radiator and washed out a beach fun of sand, and north carolina red clay mud. Didn't have any problems after that. Should of listened to my dad when hetold me to "startsimple and work up to the bigger problems".

 

Yeah, we checked the fins on the condenser, between the condenser and radiator. I haven't talked to him about it in a couple weeks, I don't know if he ever got it figured out or not. I'll post the fix as soon as I find out.