overheating, but not?

so if the jeep ('92xj, 4.0L, 5-speed,4x4, 231.) is sitting cold i.e. overnight.
and i get in to start it the temp gauge goes from 150 to past the highest reading in a matter of seconds.
with this temp reading i should be blowing hoses and super hot.
i get out to check and everything is COLD the fluid all the hoses.
i change the sending unit to the gauge ( the one in the t-stat housing.)
no go?
could it be grounding out?
i'm at a loss.
thanks.

Isn't themp sender still in the back of the head on a 92??

Not sure when they made the t-stat sender the ONLY sender, but I don't think it was as early as 92...but then I've been wrong before.

Try burping the cooling system. You may have a bubble trapped in there.

I believe Paradise is correct- the sending unit is in the head, not the Tstat housing. That should be the sensor the PCM reads. Check the picture for the location and description- if you're not actually overheating, ignore the how-to bit.

http://www.lunghd.com/Tech_Articles/Cooling/BurpAirMod.htm

yes i have that one too.
ok, i was unsure which one was for the gauge. thanks.

I do have the petcock installed in my 90 XJ and the 88 MJ (with 92+ housings) and both are converted to open cooling. I also have both t-stats drilled.

...but is the gauge sender located in the back of the head on a 92??

ParadiseXJ said:

I do have the petcock installed in my 90 XJ and the 88 MJ (with 92+ housings) and both are converted to open cooling. I also have both t-stats drilled.

...but is the gauge sender located in the back of the head on a 92??

Click to expand...

Yes, the temperature gauge/idiot light sender is in the head through 1996.