Stuck Open Thermostat?

[Colin]

Hey guys, think my thermostat is stuck open. The needle sits on cold for a long time (easily 20 mins) while driving in town, on the highway it comes up to normal after a minute or two. It's a '98 4.0L, is there a way I can check to see if the thermostat is operating properly, without ripping it out?

Also had a coolant flush last July, so that should still be ok right?

And if I do have to replace the damn thing any tips? Tricks? Anything I can do to eliminate air trappage?

Also, Stant Superstat, any good? Does it come with the hole drilled in it? And will they have them up here in Canada?

 

[Big Jim M]

hmmm!

Hey guys, think my thermostat is stuck open. The needle sits on cold for a long time (easily 20 mins) while driving in town, on the highway it comes up to normal after a minute or two. It's a '98 4.0L, is there a way I can check to see if the thermostat is operating properly, without ripping it out?

Also had a coolant flush last July, so that should still be ok right?

And if I do have to replace the damn thing any tips? Tricks? Anything I can do to eliminate air trappage?

Also, Stant Superstat, any good? Does it come with the hole drilled in it? And will they have them up here in Canada?

I would drive it about ten minutes with the temp gauge still showing "cold". Then I'd stop, raise the hood, and FEEL of the top radiator hose. If it was hot then I'd be suspecting the temp sender! If it was only a little warm then I'd be thinking of the thermostat.
You have a twelve year old vehicle. When was the last time you put a new thermostat in there? If it was mine it would already be on it's 3rd or even 4th new thermostat!
I have never had a reason to be picky about the brand of a new thermostat. However the new ones that only fail in the open position are the ones to get if you can find one.
The hole doesn't do much and shouldn't be a problem without one. When refilling keep the radiator cap off and run the engine until it reaches temperature and the thermostat opens. Keeping the level full all the while. I like to raise the front of the vehicle to ensure the radiator cap is the highest point in the cooling system. When all the air is pushed out by the open thermostat I know the system is full.
I'm betting on the sender or the wireing to be the culpret here.
Big JIm

 

[Colin]

Thanks for all the help Jim, I got the truck last July so I have no idea how old the thermostat is, but i will check to see whats up.

 

[Colin]

Incidentally, how hard would it be to replace the sending unit by myself?

 

[Big Jim M]

Anyone else there would only be drinking your beer while you did the job anyway! I'm pretty sure any of my five daughters could do that job single handed.
Big JIm

 

[Colin]

Alrighty good to know