Wonkie Coolant Temp

75 CJ5 304. New temp gauge and sensor. Gauge will stop around 150, then, most times, after I turn engine off for a few minutes, will go to about 190. New tstat. Sometimes, it works perfectly. What the hey ???

 

"Heat soak" from the block once the water stops circulating through the radiator?

 

x2, I had an old tandem Ford truck once with a 477 cu. in. gas motor. If you ran and pulled it hard at night there would be a red glow beneath the truck when you shut it down from the exhaust manifolds glowing red hot. If you turned the key back on 2-3 minutes later the temp gauge would be pegged hot. Just start it back up and idle a couple minutes, the temp would cool back down to normal.

 

Why then wouldn’t it read the correct temp while running? And why, when it works, does it work properly. Is it possible that the sensor not being in the stock position, makes a difference? The new sensor is too big in diameter to fit the stock location, so its about 6” over towards the passenger side, on the other side of the stat. It is in contact with coolant

 

Are you saying the only time the gauge goes to 190 is after the engine is shut off?

 

For the most part. Occasionally it actually does work where it’ll climb to around 195 and only fluctuate a few degrees. It tends to get stuck around 125ish

 

Sounds like the thermostat, even though it is new I would remove and test it. The thermostat you have is it rated at 190 or 195? It should begin to open around 190 and be fully open by about 205.

 

Check all the connections and wires for clean and tight. Any variation in resistance will cause funky readings.

 

I did this a couple times actually, and it fixed it for a few cycles. I did forget to mention its an aftermarket gauge with a fat cylindrical probe. As a retired electrician, I make a terrible mechanic, but, I have a thought. In it’s non stock location, is it possible an air bubble is interfering with it somehow?

 

I’m trying to wrap my head around this. It’s a 190, so, at, say 130 or so, is there only limited flow until its completely open?

 

Not sure if this helps. In this pic, you should see stock sending unit, tstat housing, oil filler, then new sending unit location

 

No, its some sort of emissions gizmo. I had thought the same, but, the probe hits the tstat

 

That’s the stock one/ location, but the new probe is too big for the hole

 

That’s what I’m trying to wrap my head around. If the tstat fails, wouldn’t it be either, closed, open, or somewhere in between? The gauge reading 125 doesn’t make sense to me in that case

 

I tend to agree. I do wonder, so I can learn, how location would matter