How to diagnose overheating engine.


I have a Ford F-150 1995 model it has a 302 in it. My question is, it keeps overheating I change the water pump about 6 months ago, it has a new thermostat also, the water wasn’t circulating in the radiator so I flushed it 3 times took it out and made sure everything was washed out of it, so I put it back in and the water is moving through it just fine now, so I figured I had the problem fixed well I don’t its still running hot . Do you have any idea what else it could be that’s making it run hot? I’m baffled and out of ideas. Hope you can help thanks. – Kirk

Here are the steps I use when diagnosing an overheating issue…

1. Check the radiator cap with a tester. A bad radiator cap will keep pressure from building and can cause an engine to overheat.
2. Pressurize the cooling system and check for leaks.
3. Have the hoses been changed lately? A soft radiator hose can collapse and restrict flow of coolant to the engine.
4. If the radiator was plugged and required a flush, maybe the engine has a blockage as well. Was any radiator stop-leak product used in the past? They can cause issues with head gasket coolant passages and other tight areas.
5. I have had brand new water pumps fail shortly after install. It’s possible that at higher RPMs the impeller is spinning on the shaft, reducing coolant flow.
6. Check airflow, fan clutch or electric fan if equipped.

Overheating issues can be a real pain to diagnose. Many shops and owners just start replacing until they find the culprit.

Good Luck,


Posted: 28th October 2013  |  Author: Kevin Schappell  |  Category: Cooling, Engine

Air Pocket In Cooling System?


Does an air pocket in the coolant system cause a leak?

Three days ago I got a dealership to replace a cracked water pump on my 2007 chevy Impala. They replaced the pump but now there is a very small amount of coolant dripping every hour or so. I took it back to the dealership and told them the problem and they told me there was an air pocket and that I was to drive normally and it would take care of itself.



If the coolant is dripping from the overflow tank, I would not be concerned about it, but if its coming from the engine, specifically from the water pump, I would say they need to fix it. Keep watch, and check the coolant level on the overflow tank to see if it drops. If it continues to lose fluid over the weekend, I would take it back and insist on them fixing it.

Posted: 23rd July 2009  |  Author: Kevin Schappell  |  Category: Cooling

Car Overheating



My 1987 ford mercury monarch sustained a broken heater hose, was towed into the garage and repaired. The mechanic ran the engine at idle for over an hour and declared it repaired and fit to drive. I drove the car about three miles, the engine light came on, the car overheated. I was towed back to the garage coolant was added again, no leaks were seen, the coolant was circulating, the engine was run for an hour, hose temp were 170 degrees and the car was test driven. Again I left the garage and again after 3 miles the car over heated and had to be re-towed to the garage. Can you give any help or explanation? The mechanic can’t explain.

Thanks for you help.




It could be a few things… The waterpump could be bad, even if the water is circulating at idle. The impeller could be loose on the shaft, and at higher engine speeds will not spin, thus causing your overheating since no water is being circulated. It could also be the belt, clogged radiator or extremely lean running condition, but my bet is on the waterpump.

Good Luck,


Posted: 5th July 2006  |  Author: Kevin Schappell  |  Category: Cooling

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