1999 Gmc Jimmy Sls 2 Door Heat/engine Problem

[Mrundle]

I got a 1999 2 (door) GMC jimmy, With 260.000 km on... Vortec Engine......
My Problem is that my TRUCK overheats when driving at lower rpms, but when driving on the highway the heat gauge is at half..... but when I drive in the city in stop and go traffic it gets to be 160 (MAX).. ALSO My engine is running really ROUGH when your at low RPMS or complete stop... What could MY PROBLEM BE?

[jdmccright]

CLUTCH FAN DIAGNOSIS (from the Haynes manual)
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Start the engine and listen for fan noise. Fan noise is usually evident during the first few minutes after start-up and when the clutch is engaged for maximum cooling (during idle). If fan noise is excessive, the fan cannot be rotated by hand while the engine is stopped or there is a rough grating feel as the fan is turned, replace the clutch.

Check a loose fan assembly for wear and replace as necessary. Under certain conditions, the fan may flex up to 1/4 in. This is not cause for replacement.
The fan clutch is not affected by small fluid leaks which may occur in the area around the bearing assembly. If leakage appears excessive, replace the fan clutch.

If the fan clutch free-wheels with no drag (revolves more than five times when spun by hand), replace the clutch.
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Proper fan clutch operation will allow some rotation when engine is off and cool, but will feel firm when the engine is hot. Overheating happens at around 230 degrees, so a temp reading of 160 in stop and go is pretty good.

Another possibility might be a balky thermostat. I have a medium-temp (180 degree) thermostat installed in my '96 and it rarely gets above the 1/4 mark. Its an inexpensive and pretty easy fix. Don't forget new hoses and antifreeze...flush it good if it hasn't been done in a while.

As for the rough idle, more info is needed. Does it only happen when the engine is cold? Hot? Anytime? Is it hard to start?

Hope this helps!

[Mrundle]

Its coming out to be 125 Degress the hotest IT CAN BE...... Its when you drive for a bit, that the temp gauge goes UP..... But the other thing is that its LOSING engine coolant.... The OIL is OK... When you drive for a bit and then turn the truck off, you can hear a sizzling sound, sounds like its coming from where the oil stick is or somthing???? But the Engine Sounds and Runs like SHIT... and its like thumbing... or like hesitating....

[jdmccright]

Your 125-deg temp is not at all a normal engine coolant reading (from the instrument panel)...it is very low. Normal coolant temp range is 185- to 210-deg. I am wondering where you are getting your temp readings from. Are you reading this from your instrument panel or are you measuring from an air duct? That said, if your 'Check Gauges' light is coming on and you're coolant temp needle is in the red zone, then yes you have an engine overheating problem. Either add coolant or check the thermostat and fan clutch as mentioned before.

Alternatively, if you mean that you're cabin air is too hot and you cannot adjust it then you will need to have the temperature select switch and mixing door servo motor checked.

Finally, hearing sizzling sounds from the right side of the engine is a definite indication of a water-based leak. Does it smell like engine coolant inside the engine bay? Any other pungent smells? Do you notice orange-colored drips underneath the truck's engine bay or anywhere else? If the aluminum skid plates are under the truck, they can "catch" the drips and make them fall elsewhere or mask a small leak by acting as a drip catcher. Unbolt them and see if you notice any signs of coolant collecting within the ridges. Then look under the engine for any orange-colored drips and follow them back up to the source. My guess would be a leaking heater core hose that is dripping onto the hot exhaust header, which is routed through the right side of the firewall. It may be a hose clamp that has loosened or just an old hose that sprung a leak after all those kms. You may be able to borrow a coolant system pressure test kit to pressurize the system while the engine is off to pinpoint the leak.

[b1lk1]

Originally Posted by boyd.r

1999 jimmy is overheating can the lower intake gasket leaking cause this.

Probably not unless you are letting the coolant level get really low. I ran my truck for 5 months with the gasket leaking with no overheating issues.

I suggest you start your own thread to try and get answers for your truck since alot of people (not me) get cranky when they see old threads dragged up.