Temperature gauge fluctuates after changing thermostat

[JeffWS]

I changed the thermostst (using MotorcraftRt-1137) and now the temp gauge moves from just above cold to just before the middle of the gauge, and back again. I suspect air in the system, but I have tried various ways of getting it out. Ran engine with the cap off, filled system. Also pinching upper hose with cap off. Anyone have this problem, or know the fix?

 

[McCormack]

The temperature fluctuating is pretty much normal with a new thermostat. Keep an eye on it for a couple of weeks and I think you'll find that it will eventually stabilize.

 

[buckshotmudder]

What McCormack said. If you have a steep incline let the engine cycle through 2-3 times with cap off and top off. Other than that the fluctuation is letting you know its working properly.

 

[RonD]

Why did you change the t-stat?


Look at the heater hoses in the engine compartment and see if you have a 2 port heat control valve or a 4 port bypass heat control valve.
If its a 2 hose then never mind, but set heat to HOT when trying to clear air from the system.

If its a 4 hose then that bypass may be why temp is going up and down, it could be partially blocked.
In some models they needed a bypass for the cooling system, they used the 4 port unit as that bypass, in my '94 4.0l they used the heater core itself, when that got partially blocked, still blew warm air, it cause the gauge to go up and down as you described.
And I replaced my t-stat, and fan clutch, lol.
Then I read a post here that the heater core or bypass valve could be the problem, saved me from buying a new rad

 

[JeffWS]

I changed the thermostst as just preventative maintenance. LOL

Should have left well enough alone.

My engine is a 3.0, so the heater by-pass doesn't apply.

 

[Jarhead504]

I was going to post the same question. I just changed the thermostat and ECT (I think that's what they call it) and have been driving it for only four days and the temp gauge would not come up past the "normal mark", the first mark. Then it bounced around from the bottom back and forth to that mark. It has settled down and is no longer bouncing and sits perched on the first mark. I was guessing the bouncing might have been due to air in the hoses.

Do they sell them in different temperature ranges? Is it possible to have the wrong one? This one is working now but I was thinking they might have sold me the wrong one.

Jarhead504

 

[Rearanger]

Sorry guys but I've never had gauge fluctuation from a new thermostat. Either the stat is defective or there's another issue with the cooling system.

 

[JP02XLT]

A little fluctuation as it is warming up, but within 20 miles or so it should be pretty steady, maybe move up or down a needles worth from norm.

The air is really a pain to get out of these Rangers at times, I would do the rubber glove on the radiator, head gasket test.

JP02XLT

 

[McCormack]

Ranger 3.0 engines have their heads below the engine's coolant outlet to the radiator, and the coolant outlet to the radiator is below the radiator coolant inlet, and seeing as air rises in a fluid, any air that's in a 3.0's coolant system will float uphill towards the radiator and thus there is little chance that air will be trapped for any period of time in a 3.0 engine.

I've changed thermostats 3 times times in my '00 Ranger, and every time I did it my temperature fluctuated for awhile, and then eventually settled down. It's completely normal and nothing to be worried about.

 

[JP02XLT]

Is the heater core higher than the cap? I have not looked at mine recently, but If memory serves me correctly, I remember its close.

JP02XLT

 

[LilDirty91Xlt]

Reviving this post

I change temp sensor when I first bought my 91 3.0 ( It wasn't working ) For a few days the gauge danced around like Miley Cyrus, then settled into a more Hanna Montana role.