Thermostat sticking on GM 4.3?

[nomochevys]

Hello, I have a problem and not sure what is causing it. This is on a 96 Gmc truck with a 4.3 V6 engine. I start the truck up and it runs fine and as it warms up the temp gage does not stop at the usual 180-190 mark. It pushes right over to about 230 and stays there for maybe 5-10 seconds and then comes back down to 180-190 fairly quick.

This scares the bejesus out of me thinking that is is going to over heat. The water pump is only a year old and there are no leaks that I can find. It only does this as it warms up and you can drive it the rest of the day any distance and the temp gage stays steady where it always has at 180-190.

What is causing the spike in water temperature?

 

[Chris142]

low on coolant or a lazy stat

 

[DemoFly]

Thermostat is getting fat.

 

[SLCraig]

I'd check the coolant level as said before, and start by replacing the stat if the level is fine. Stat is the cheaper and easier place to start.

 

[JHZR2]

Id replace the thermostat and do a good coolant flush while at it.

Lots of thermostats are faulty with so much third world junk coming in. Put yours in a pot of hot water with a thermometer, and make sure it opens at the right temperature!

 

[eljefino]

On your new stat drill a tiny hole in its flange if it doesn't already have one. This helps with water flow that "tickles" the brass pellet. Also burps air, if any.

 

[SatinSilver]

If you replace the stat go with an oem version. Much better quality. Afterall it protects a very important item in your car. Kind of worth it to pay a little more. Plus it will probably last much longer than some of the aftermarket stuff out there.

 

[JHZR2]

Originally Posted By: eljefino
On your new stat drill a tiny hole in its flange if it doesn't already have one. This helps with water flow that "tickles" the brass pellet. Also burps air, if any.


I assume at the topmost point relative to how it is installed?

 

[nomochevys]

Ok, Im going to change the thermostat and see what happens. Im pretty sure it original. Where do I get a OEM part? Gm stealership? Its so confusing buying parts anymore because I dont know who to trust. 3/4 of the stuff is made in China even if it comes from the dealerships. Is there a particular brand to buy or look for? Thanks.

 

[eljefino]

Originally Posted By: JHZR2
Originally Posted By: eljefino
On your new stat drill a tiny hole in its flange if it doesn't already have one. This helps with water flow that "tickles" the brass pellet. Also burps air, if any.


I assume at the topmost point relative to how it is installed?


yes but on his truck I'm pretty sure it sits flat so it could go anywhere.

If you can't get a dealer part get a stant superstat or (rare) robert shaw.

 

[wtd]

Also check the radiator cap as it plays a big part in temps as well and I would go OEM on that as well.

Wayne

 

[mechanicx]

To determine if it's ACDelco OE or if it's ACDelco Professional is based on part number. 131-151 should be the OE t-stat. It probably runs around $15 and no one locally may have it besides the dealer. If not going with OE I would go with a Stant superstat.

 

[nomochevys]

Well, I bought a stant thermostat for 9 bucks at AAP. Its made in the USA. But, I think I have bigger problems. Popped the hood this afternoon and had no coolant in the overflow tank and took off a pretty new cap on the radiator and could not even see any coolant in it. There are no signs of leaks anywhere. I have a feeling the coolant is disappearing into the oil via the infamous intake gaskets.

Ugggg! The coolant tank has a sludge like coating on it and the radiator looks pretty rough and nasty to me. This is not looking too good right now.

Is it ok to add coolant into the overflow tank? Sorry if that is a dumb question.

 

[wtd]

I would also bet you have the intake gasket leak. I have had the intake manifold gasket replaced on my 98 Z71 with the 5.7L three times in 14 years and 121,000 miles. Common problem on this family of engines. Have an oil analysis done to determine if it is going into the oil if you can't obviously see it.

Oil analysis is how I caught my leaks the last two times.

Wayne

 

[yonyon]

Don't make that assumption just yet. If coolant is draining into the oil your oil dipstick should read high. You might also notice the oil doesn't look right, and if you open the drain plug a little, some coolant should flow out before oil. If you can observe none of these, your coolant probably isn't in the oil pan. On the other hand, it is a common problem so you need to look for it before you do too much else in your search.

That said, it's possible for a gasket such as an intake gasket, a radiator tank gasket, or a water pump gasket to leak only while cold. Pressure testing while cold can be worthwhile. Don't forget to check the floor on the passenger side.

If you do all this, and probably other things some people will suggest soon, and you still can't find a leak be sure to look at your spark plugs for signs of coolant. Head gasket leaks on the 4.3 are rare, but I've seen a couple. This engine makes it almost impossible to look for steam cleaned piston tops without a boroscope, so spark plugs make for a good first look.

 

[nomochevys]

Thanks, I just changed the oil and did not notice anything unusual. It was also not over full so I may be jumping to conclusions. The infamous leak was always in the back of my mind so I may have jumped to conclusions to soon.

Thanks for all the advice.

 

[yonyon]

Consider also that crud and/or goo may be hiding a leak by slowing it down. A flush to get some nastiness out might make the leak easier to find.

 

[edwardh1]

Originally Posted By: eljefino
On your new stat drill a tiny hole in its flange if it doesn't already have one. This helps with water flow that "tickles" the brass pellet. Also burps air, if any.


good comment
many oem stats have the hole
replacements dont
seems a hole would be real cheap to install on the assembly line