Car Doctor Q&A: If You’re Gonna Throw Parts at a Problem, Start Cheap

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The best way to find out what’s wrong with your car is to diagnose the problem, rather than just throwing random parts at it. Good thing John Paul jumped in before an unnecessary head gasket replacement still didn’t fix the problem.

Q. I have a 10 year old Chevy TrailBlazer with the smaller V-8 engine, and it has an odd problem.

Sometimes it will start to overheat, when this happens and I open the hood the upper radiator hose is completely flat. If I let the car cool off and add water it is fine again. I can drive for several days and it will be fine and then out of nowhere it does it again.

So far I have replaced the hose, the water pump and the thermostat. I’m afraid at this point the engine has a head-gasket problem. Should I give up on it and commit to replacing the head-gaskets or hope some sort of magic additive fixes the problem or just trade it in?

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A. Certainly all of the items you replaced could have been faulty but I think you overlooked the cheapest and easiest fix.

More than likely the radiator cap is faulty. As the engine gets hot and pressure builds in the radiator, coolant travels through the overflow line from the radiator into the surge/expansion tank. As the engine cools, antifreeze will be pulled back into the radiator. If the radiator cap is not functioning correctly it can’t pull the coolant back into the radiator and typically the upper radiator hose will collapse.

Replace the radiator cap with one that is the correct type and pressure rating, and your engine’s collapsing hose should be resolved. Hopefully when the truck was overheating it didn’t damage the engine.

If you still have a concern about a head-gasket issue you can buy a “block-check” kit, that tests for exhaust gases in the cooling system.

John Paul is public affairs manager for AAA Southern New England. A certified mechanic, Paul tests dozens of new cars each year and also hosts a radio show on AM 950 and 550.

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John Paul