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Repair guides and support for the second generation of C/K pickup trucks.

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truck maybe overheating after 25 minutes?

77 chevy C-10 straight inline 6 ..take trash to dump every 2 weeks, only runs 25 minutes then i get home radiator bubbling boiling into overflow.....Thermostat or water pump?....Would not think it would get this hot in 25 minutes..

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Thanks guys, i just bought a thermostat, i'll pop that on there to see if it's the issue......Somebody told me one time you could take out the thermostat and run the vehicle but you won't have heat...Is that something that's ok to do?


@acura Not quite, one of the functions of the thermostat is to keep the water inside the engine block when it's cold so the engine warms up faster. That means it will take longer for the engine to warm up, delaying the time until your heater starts putting out warm air.

But more importantly, while the truck is running it helps regulate the water temperature for the engine's best operating temperature.

So yes, you can run it without a thermostat, but given they're cheap and easy it doesn't really justify running without.


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I agree with Jerry, most probably the thermostat is not opening. It could be any of the other things he mentioned but the thermostat is most likely the problem.

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You shouldn’t run a vehicle without a t-stat because sometimes it lets the water circulate through the motor and radiator too fast and then it won’t cool down in the radiator as it should.

You would possibly have heat but it would take longer to get warm air.


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Hi Sam,

No, in 25 minutes an engine can easily overheat if the cooling system isn't working as it's supposed to.

You're right that the thermostat and water pump are the two most likely causes, but they're not the only possibilities either.

Assuming you've verified that your coolant level is correct and you're not just low on antifreeze, then I'd check the thermostat first, especially since it's cheap and usually not difficult to replace. You can actually test it if you're so inclined; to do that you put a pot of water on the stove with a thermometer in it. Place the thermostat in the water and turn the burner on. Watch the thermostat as the temperature rises; when it gets to the temp the thermostat is rated for (usually somewhere between 160 and 190 degrees; it may be printed on the thermostat itself), the round plate on the thermostat should open up. If it doesn't open by the time the water gets to boiling then it's time to replace it.

If the thermostat tests good, then it's time to look elsewhere. The usual failure mode for a water pump is the bearings going out, resulting in it failing to pump efficiently and allowing pressure to escape. Manufacturers have built in a "weep" hole in the bottom of the pump where antifreeze will leak out of if the seal has failed, so look at the bottom of the pump and see if you've got coolant dripping out of the weep hole. If so, it's time to replace the water pump.

Off the top of my head, other things that can go wrong would include the radiator being plugged up. Run the engine until the radiator gets hot, but not so much that you can't touch it. Feel the temperature over as much of the surface of the radiator as you can; if there's a blockage you'll feel a definite temperature difference between one part and another. Normally the temperature will be fairly even across the whole area. If you find a significant cold spot then it's time to replace it or take it to a repair shop.

Check the radiator hoses for any sharp bends that could be restricting the flow of water through them; that's another possibility.

The last thing I can think of would be if your head gasket is blown, that would allow pressure from the cylinders to escape into the cooling system and cause your overheating. Check the coolant for contamination from oil mixing with it, and also check the oil; if it's brown and frothy, a blown head gasket may be letting oil into the water or vice versa.

I think I've covered the most likely scenarios; if there's something I've missed I'm sure another contributor will help out by mentioning it.

Good luck with your truck!

EDIT: I did think of one more thing to check; the fan belt. A missing, loose or damaged fan belt will fail to drive the water pump and result in overheating.

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I replaced the thermostat and drove around for about 45 minutes or so...Came home check under hood & no issues...No bubbling, boiling sound & no water going into overflow....I think it's fixed...Thanks guys!

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Awesome, Sam! Glad to hear it.


Great news. Thanks for the update.


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sam zal eeuwig dankbaar zijn.

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