Overheating dilemma

Either water is flowing through radiator to fast because of no thermostat.

Or there is not enough air flow through the radiator.

Makes sense, but like the OP, I’m wondering what changed, since it supposedly didn’t have an overheating issue in the past…

The amount of dead bugs blocking the air flow.

Maybe… But I doubt it unless they’re in a love bug or locust country.

Have the trans cooler, but I have not figured out a way to test the radiator. Local radiator shops will not service an aluminum welded tank. Radiator is clean and debugged

Common causes beyond what you’ve already done

  • cooling system isn’t holding the correct pressure. this can occur even though there is little to no coolant loss.
  • air pocket in cooling system
  • head gasket problem
  • radiator is clogged, ether air-flow or water-flow parts
  • clogged coolant path inside engine
  • a/f mixture too lean
  • ignition timing not to spec
  • valve timing not to spec

I’d check the ignition timing and a/f mixture, and if those check out ok then the next step would be a cooling system pressure test.

Thanks. Have checked off these with the exception of radiator internally. I have not determined how to properly eliminate the radiator as the source of the problem yet.

You can use your IR thermometer to run across the tubes of the radiator. If it is a cross flow, then run the IRT vertically, if it is top to bottom, then go across. Look for a dip in temperature in an area. Most of the time, it the radiator is clogged, you can look at the tops of the tubes in the tank and see lots of mineral build up around them.

I do wonder that if you replaced the water pump and the radiator cap at the same time, if the old radiator cap was the problem, now resolved, but possibly you installed the wrong water pump.

The old style water pump pumped coolant into the bottom of the block and came out through the heads. The thermostat was at the top of the engine. This is the type you use for cast iron heads. The new style reverses the flow and is for Aluminum heads. There were some late 350’s with aluminum heads

For the water flow test I expect a radiator shop fills the radiator full of water. This is usually done w/the radiator on the test bench, they just hold their hand over the outflow hole at the bottom, radiator cap off. Then they remove their hand and time how long it takes the water to drain out. Either that or they time how long it takes the first gallon to drain out. They have benchmarked this test using new radiators so they know what the flow rate should be.

For the air test, not sure how they do that. One idea, you could tape a big piece of white paper on the wall, shine a light on it, and see how much light gets through the radiator by peering through it. I doubt they do it that way, they probably just look at the fins, and straighten out any that are blocking the air flow. Those fins can be bent by spraying water too forcefully at the radiator in an attempt to clean it. Ask me how I know this. … lol … I had a big job on my truck straightening out the fins after I pressure washed the radiator some years ago.

You have an IR gun?

When the engine starts to run hot, point the IR gun at one of transmission cooling lines going in/out of the radiator.

This is what the temperature you read means.


Not seeing it mentioned, but have to ask.

Did you recently convert from V-Belt drive to serpentine belt for the water pump and accessories ?
Or replace water pump for some other reason before this problem started ?

Just thinking water pump might be turning wrong direction.