T-stat closed, no overheating, WHY?

[J. Kennedy]

The needle on my X has almost always been in the cold region, since new. It would never go above the "C" line. I mentioned it to the dealer every time it went in for service while it was under warranty, and of course they said it was normal.

I had the thermostat replaced around 40k, and the needle crept up around 1/3 of the way above cold. After a few months of this, it went back down into the cold range.

Last nite, I tested a new thermostat in a cup of boiling H20, and it opened fine. I installed it, and the needle is now again 1/3 above the cold line. I tested the old (2nd) thermostat, and it would not open at all!!!

If the stat was always closed, the hot coolant should be trapped in the head, and the engine should have cooked. But this never happened. In fact, the engine always ran cold. WHY? Any thoughts?

 

[Hartman]

If it stays in the "C" region that means it's stuck open. It's allowing the coolant to enter the block at all times, thus never letting the engine to warm up. The coolant is still being cooled by the radiator/fan, so it won't be any hotter than normal.

There are a few reasons why this is happening.
1. You installed the t-stat backwards. (Spring end goes into the block)
2. The sender for the gauge has gone bad. This is common.

 

[J. Kennedy]

I would say no, on all counts It acts as if it were stuck open, but when I pulled it it was closed, and remained closed when bench tested. Like it is welded shut. So its not that.

All 3 Tstats were installed correctly, with the spring into the head. The Factory one, the Dealer replaced one, and my newest one. #1 never worked, #2 worked for a few months, #3 is working at least for now. So its not that.

The Sender & guage test ok, plus the needle has always moved corresponding to engine temp. So its not that.

Is there some saftey system that bypasses coolant thru the heater core in the event of a thermostat failure? Im really banging my head on this one.

 

[J. Kennedy]

right, but since it was closed under all circumstances, we can assume it was not stuck open. If by "winter thermostat" you mean higher temp, 195 is the highest they sell. Lower temp ones are for perfomance mods that cause the engine to run overly hot. I had the opposite problem.

 

[410Fortune]

a thermostat opens at a particular heat range, not by pressure in the cooling system.

 

[410Fortune]

Oh dont sweat it man! hahaha I do the same thing all the time....

A good way to get some feedback is by posting something you think is right, then people who know you are right or wrong will chime in.