Was driving home from work and have a hill to climb, 1.3 miles at 6% and a warning light came on and temp gauge was at max. I pulled over and shut the engine off, popped the hood. Nothing about the engine seemed hot. The radiator was cool enough that I could lay my hand on it. I then turned the ignition on but did not start to see if the cooling fans would turn on, they did not. Looked at the guage again and it was at normal hot.

Got in and drove it about 1/2 mile, I was near the top of the hill, the temp started moving rather quickly to hot again. Pulled over and the temp dropped to normal hot immeadeatly. It was down hill for the next 5 miles so drove it home. The temp would go up some and then back to normal.

I turned on the A/C and the two fans did start running.

I thought that it might be low on coolant. Got it home and let it cool to check the radiator for coolant. The overflow bottle was at normal level and the radiator was full to top. The belt was on and turning and the water pump has about 20k miles on it.

Could this be a bad thermostat or could the temp sending unit be failing?

I plan to replace the thermostat tommorow. Just where is it located? I assume it is where the radiator hose connects to the engine underneath the spark coils.

 

Haven't gotten the thermostat yet but I drove it again today and the temp went up over normal and then back down below where it normally runs. I am seeing changes in the gauge that were never there before. I do thnk the thermostat has had it.

I'll change the thermostat and if that does not correct the problem then the temp sender will be next to be changed.

 

If the engine itself is overheating and the feed hose to the rad and rad itself are cool my first thought would be thermostat. I'd be tempted to verify the temperature by an independent means (temperature gun or similar), but if the engine actually is as hot as the gauge is indicating I'd swap the thermostat and see where you get.
I wouldn't throw a temperature sender at it until you have verified whether it is actually as hot as the gauge indicates.

 

I replaced the thermostat and it did not correct the problem. I did a cluster test and the gauge checked out.

I drove it with the new thermostat and when the gauge went over the half way point on the gauge it rapidly went to hot. I stopped and the fans were running. The hose from the engine to the radiator was very warm but not hot enough to keep me from holding it. There are no other symtoms that the engine is overheating.

I will put a temp sending unit on it tomorow.

 

possible pump issue. might be not flow at times.

 

I gave the pump some thought and I will replace it if the sending unit does not correct the problem. The impeller could be loose on the shaft. It is also possible that the hose from the radiator to the pump is collapsing and reducing the flow of coolant.

The engine does not appear to be overheating when the gauge is pegged hot. I have seen overheated engines before and this one appears to be at normal operating temps. I will have the sending unit later today.

 

Replaced the sending unit and it did not change a thing. As soon as it cools down the water pump will come off to be inspected. I have never heard of a water pump failing before the bearings fail. The hose from the radiator to the pump will be the next thing to check and if it is soft it will be replaced.

 

Found the problem!!!!

Replaced the radiator hoses and that did not fix the problem.

Just removed the water pump and the impeller is spinning on the shaft.

Taking a break and then will put it back together.

 

Does the water pump have a metal or plastic impeller? I've only ever seen that with plastic impeller pumps on VWs and Audis.

Good to hear you pinned it down!

 

It had a plastic impeller. It could spin like it had ball bearings.