99 Jimmy Overheating

My 99 Jimmy has been overheating. A new water pump was installed. It has been at the GMC dealer for several days. After $1000.00, it came home and still has a sound under the hood like water boiling on the stove.

Well your overheating problem could be the result of several things. What exactly was the 1000 dollars spent on fixing? Well if you want to check the problem out for yourself, here's a couple of things you can do:

1: Start the engine cool, grip the upper part of the upper radiator hose firmly, near the thermostatic housing (be careful of the fan if it turns on) to see if there is any coolant passing through. If there is coolant not flowing through the upper house once the engine warms up (check the engine temp gauge to see if its warmed up) you should probably get the thermostat replaced because it's probably stuck shut and is not letting the coolant circulate to do its job.

2: Another problem could be the fan. My other car had a bad fan relay which didn't let the electric fan run once the engine warmed up. Check to see if the fan turns on once the engine warms up. If it doesn't one of the components of the fan isn't working.

One more thing, make sure to fill up the radiator (to the top) and expansion tank (to proper level) and then start the car to check the cooling system as described above.

Hope this helps. If everything checks out OK, feel free to post here again.

The rad cap that came with your vehicle is faulty. They wear down and do not seal properly allowing air into your cooling system. Replace it with a cap that is not ACDelco - mine is a Stant brand. The air in your system is the water sound you hear.

Lower intake gaskets are also a common problem. Did the dealer replace it?

Was the cooling system reversed flushed?


My 99 Jimmy has been overheating. A new water pump was installed. It has been at the GMC dealer for several days. After $1000.00, it came home and still has a sound under the hood like water boiling on the stove.

Replace your rap cap with something that is NOT AC Delco.

You have air in your system and the rad cap is not allowing the system to purge the air out.

The air you are hear is in your heater core.

Replace the rad cap and all should be well.

The rad cap that came with your vehicle is faulty. They wear down and do not seal properly allowing air into your cooling system. Replace it with a cap that is not ACDelco - mine is a Stant brand. The air in your system is the water sound you hear.

Lower intake gaskets are also a common problem. Did the dealer replace it?

Was the cooling system reversed flushed?


The intake gasket was replaced, the water pump was replaced, the fuel pump was replaced, the ac compressor was replaced. The radiator was flushed. Tonight I drove it and the same noise. There is liquid coming out of the overflow location. I have a new cap I bought myself to put on. Do you have any further ideas.

Is there enough coolant in your system? There should be enough coolant in your plastic reservoir to allow only coolant and no air to be sucked in. Check the level on the plastic reservoir.

In the morning when the engine is cool, open the rad cap ... is the coolant up to the brim ? it should be ...

is engine still overheating or now just the noise?


also, maybe a long shot but ...

I recently heard a noise from inside my truck coming from the heater core area. I thought it was air in the system but, I had recently changed the intake gasket, flushed, changed the water pump, etc. I knew it couldn't possibly be the cooling system. Then, I thought maybe it was ticking lifters ... well, it took me weeks to find the problem ... it was the plastic windsheild cowls! they had cracked and come loose and were vibrating and chattering which sounded a little like the bubbling sound ... there's also foam under there which had loosened and was no longer suppressing the plastic from vibrating ...






The intake gasket was replaced, the water pump was replaced, the fuel pump was replaced, the ac compressor was replaced. The radiator was flushed. Tonight I drove it and the same noise. There is liquid coming out of the overflow location. I have a new cap I bought myself to put on. Do you have any further ideas.

Make sure you used a cap that is NOT AC Delco and is rated at the right pressure.

Also, is the resevoir up to the right level, you will have to drive for a while to get all the air out.