GMC sonoma getting hot fast

Hello, I have a 1999 GMC Sonoma that I bought four years ago used with 90,000 miles on it. For the first three and a half years it ran a normal temperature but recently my power steering pump locked up and the belt came off and it ran long enough without a belt turning the water pump to get hot. I replaced the power steering pump and put a new belt on it but now after just about five minutes of light driving it will over heat. Any ideas on what is going on? I also replaced the lower radiator hose at the same time as the power steering pump was replaced.

I appreciate any replies

Does your coolant level keep dropping with no obvious leaks?
Any check engine light? Post the codes, please.
Have you considered that a head gasket has failed from the overheat?

I’d get a test kit to check for combustion gasses in the coolant. Amazon has them. I’d also rent a coolant pressure test kit from the parts store. Usually free. If either tests fail, I’d run a compression test.


Thank you, I will check the items you listed.

Remove the radiator cap when the engine is cold.

Start the engine, and as the engine idles. watch the coolant in the radiator…

If bubbles begin to form in the coolant as the engine idles, it indicates a blown head gasket.


Is the serpentine belt routed correctly ?
On some engines it’s possible for the belt to fit wrong and spin the water pump backwards

Smooth side of belt on smooth pulleys, grooved side of belt on grooved pulleys.

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Can you also please tell us what engine your 1999 GMC Sonoma has?

buy a test kit that looks like this . . . just google the word “coolant block tester”

If the test fluid turns yellow, you’ve got big problems


Before you buy any test kit, here’s a very quick thing you can do . . .

Go outside and pull the engine oil dipstick and post a picture of the oil showing on the dipstick

Also . . . regardless of the engine in your Sonoma, the coolant pressure cap is on the radiator

If the engine’s cold, you can remove the cap and post a picture of what it looks like inside the radiator neck. If it looks like Starbucks moccha frappuccino, you’ve got big problems

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If the head gasket checks out ok, you may look at the thermostat, it has a bimetallic spring that is heat sanative and can distort when over heated… could be sticking closed…


Besides all the advice above, I would check to see if you have air in the coolant system. if you overheated and had to add coolant then there is a possibility that you have air in your system causing it to get hot.

Yet another idea, the cooling system may no longer be holding pressure correctly. Ask your shop to pressure test the cooling system. Inspect the underside of the cap that sets the cooling pressure too, you may see something obviously wrong, broken gasket or spring, etc.

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