How to trouble shoot thermostat

[jhenegh]

Any good way to trouble shoot a thermostat? I know the factory gauges aren't much for accuracy, but mine will go during normal driving anywhere from the bottom of the "N" to the "M", but typically on the "N" (real scientific right?)(additional gauges in the grand plan, but aren't installed yet). Heat works fine and she warms up quickly into the normal range, I'm just not sure if the thermostat is opening sooner than it should in some situations.

I have a cheap infrared heat gun that I use to troubleshoot wheel bearings etc., but haven't shot it at the radiator to see what it says there while running. Plus, this time of year, I don't think the radiator itself will ever see 180 degrees.

Thanks

 

[riotwarrior]

remove it, stick it in a pot of water add a thermometer and then turn up the stove and watch it when it starts to open when fully open...and record temperatures...

Ya that's it...plain and simple!

 

[OLDBULL8]

To see if the t'stat is working properly it has to be removed. Set it in a pan of water with a thermometer, it should start to open at ~180* and be fully opened at ~195*. It's marked on the t'stat what temp it is. If it's a Motorcraft t'stat it will have a rubber ring around the part that goes toward the head, that is the correct one to use on these engines. If your sensor for the cold idle solenoid and cold advance solenoid is working, the cold idle and cold advance solenoids will de-energize at ~120 head degrees, with your non-contact laser gun shootn the outlet of the t'stat housing then, should be relatively cold, when the t'stat starts to open, then it should be at ~180*, all this at idle speed. Any temp on up from there would depend on engine load. You would have to see if those temps coincide with your gauge.

 

[franklin2]

A way that requires less work is to start the engine cold, take the radiator cap off, and watch the fluid in the radiator and feel the top radiator hose as the truck warms up.

If you have fluid moving in the radiator as soon as you start the truck, the thermostat is stuck open.

One problem with a diesel though, they never warm up. On a gas truck you can wait about 15 to 20 minutes, and the engine will heat up enough to see the thermostat open. You can then see the coolant start to move in the radiator, and you can feel the upper hose getting warm. But you might be there all day waiting for one of these diesels to warm up enough at idle to open the thermostat, it may never open just sitting there in the driveway.

 

[jhenegh]

Ya I guess I shoulda specified, test while IN the truck. If I'm pulling the tstat out, a new one is goin in regardless.

Cold idle works well, clicks off after about 6 minutes, temp gauge is just starting to move then. Should I be able to hear the cold advance?

 

[OLDBULL8]

I usually go into great detail to explain. No you cant hear the cold advance solenoid, unless you take the wire off and repeatedly touch it to the terminal on first cold start up, if you have a loud knocking diesel and ain't half deaf you might hear it

 

[whiteboyslo]

One problem with a diesel though, they never warm up. On a gas truck you can wait about 15 to 20 minutes, and the engine will heat up enough to see the thermostat open. You can then see the coolant start to move in the radiator, and you can feel the upper hose getting warm. But you might be there all day waiting for one of these diesels to warm up enough at idle to open the thermostat, it may never open just sitting there in the driveway.

Mine will warm up idling in the driveway. Takes about 20-30 minutes, but it'll do it.

Mike

 

[riotwarrior]

Ya I guess I shoulda specified, test while IN the truck. If I'm pulling the tstat out, a new one is goin in regardless.

YES you should have done exactly that...I had suspected you wanted an in truck test but thought I would be smarmy and just tell it like it is!

 

[franklin2]

Mine will warm up idling in the driveway. Takes about 20-30 minutes, but it'll do it.

Mike

Have you turned up your IP some? That may make a difference, mine is stock with no turbo. I messed around with a co-workers truck that was a factory 94 turbo, and someone had turned the pump up too much,, blowing too much black smoke. I turned it down 2 flats, and he noticed it took several more miles after that to get any heat out of the heater in the cab. That ended up being too much and I turned it back up 1 flat, but it definitely seems to affect how quickly the engine warms up.

 

[79jasper]

On my 88 I was able to hear the difference when the cold advance went off.

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