1987 GMC Jimmy Temperature Problems

[14hatchie]

Hey gals and gals I need some help. My Jimmy temperature gauge keeps surging. Replaced new gauge and temperature control switch on the block, but temp. still surges. I replaced the thermostat twice and got the air pockets out. On both thermostats I replaced, the temp. would get 35 degrees above the rating then open up and drop to operating temp then immediately rise back up. What is causing this flucuation? Could it be the water pump is missing a vane or 2? Any help would be greatly appreciated.

[Sodell]

This could be a myriad of things. Is it overheating? The water pump could be going out, that is possible. Your radiator could be clogged. Open the radiator cap and then run till warm. See if the water is running through the radiator.

[14hatchie]

no it is not overheating. with the 160 degree thermostat it gets to 195 before it drops. and with the 195 thermostat it gets to 230 before it drops. Craziest thing i have dealt with on this vehicle. thanks for the reply

[Sodell]

Your water pump is probably working. I would flush the radiator with some good flush.

[cadillac_al]

It sounds like the gauge is consistently 35 degrees off with either thermostat. Probably should invest in a cheap infrared thermometer to verify.

[14hatchie]

Thanks for the replies. I still dont know why it flucates. I thought when the thermostat opens, the temp. will stay constant after that. I will try and flush the radiator first then go from there. Thanks again

[gchemist]

What brand is the thermostat? Drill two small holes on the thermostat.

[14hatchie]

I believe it is a Murray from oreilly

[donut]

What are you measuring temp with, what gauge?

Btw, if rad is cooler than the thermostat, it will keep fluctuating until it all balances temp wise. At least mine used to.

[14hatchie]

I was using the factory gauge then installed a aftermarket gauge and they are both doing the same thing. I haves used 2 different thermostats and they are both opening and closing.

[14hatchie]

I can take it on a 30 minute drive and it flucuates the whole time

[willett]

This may sound dumb, but is it at all possible that you installed your thermostat upside down?

[donut]

Sounds like you've got the same "problem" as I had on the '73. Never did "fix" it.
I thought maybe it was the location of the senders. Mine was 1 in the intake, 1 in the waterneck. (basically both sides of the thermostat.) Didn't adapt the sender for the head as they were vortecs and it wasn't that big an issue. The only time it leveled out was when it was in the 90's.
This was the HD GM cooling for the truck.

Hopefully someone will have some ideas for you. My "cure" was sell the truck. It ran that way for a couple of years.

[14hatchie]

Thanks, I'm still working on trying all things mentioned

[clapage6]

at first i was thinking this could be a fan clutch but if it flunctuated an entire 30min. drive. I would probably rule that out.

My next question is, have you tried a different sender? I would try that if not. they can do weird things.. lastly

My last guess is air in the system. This can sometimes cause 2 things. The first is the air pocket hitting the sender which gives an off reading COULD also open and closes the thermostat at an irregular time.

[14hatchie]

Well it's not air in the system and I drilled a hole in the thermostat. Still no luck on fixing the problem. Also it doesn't appear the lower radiator hose is collapsing. I guess next is to clean the radiator. Anybody know how to check the water pump if its not leaking?

[14hatchie]

Well radiator is cleaned and still temps keep rising especially under acceleration. With the 160 thermostat temp gets to around 200 then drops, and with the 195 temp gets to around 230. The only reason I dont want to go back to a 160 is winter is coming and I want some heat. Maybe I should go with a 180 and maybe split the difference. I am not hearing any boiling in the radiator, which I thought I would if the gauge is reading 230-240. The fan seems to be working properly. This is 1987 with tbi, so could it be a computer issue? I dont want to buy a new radiator and water pump, but it looks like that maybe the next. Thanks for the help

[tucsonjwt]

I like the simple approach. I would take the radiator out and let a radiator shop check it. If it is defective, then I would just get a new radiator - don't waste money on repairing an old radiator - new radiators (copper/brass) can be had for about $120-$140.

[Rich84]

Mine did the same thing...2 9/32" holes in my 180 thermostat fixed the problem..but mine would only spike the first time the stat opened, then it would be fine.