i am having the same problem with my wife's Grand Cherokee. it always seems to read at 155-160 with a brand new 195 t-stat. did the same thing with the old t-stat. the fan in working fine cause we drove to Vegas with the A/C on full blast and it started to get hot and the fan kicked in like it is supposed to around 210 or so. it only gets like 15mph on the freeway like this (V8 4x4 all time) is there anything else that could cause this? also where could i get a actual water temp reader like a thermostat so i can actually measure the water temp at operating temperature?

 

15mph, now that's slow. LOL Again, how's the heater work? Check for loose/broken temp sending unit wires, the sending unit/gauge themselves, etc.

 

The temp sending unit is the one on the block right? Is it possible I culd be getting to opetating temp and the gauge is just off. Because my heat works great its just my mpgs suck. I get around 15 highway also. And it seems to be running a little rich.

 

Coolant sending unit is usually in the head on an in-line motor, not sure about the sending unit on a '95, '98 sending unit is in the t-stat housing (head). If coolant temp is actually at 150-160, heater performance will be iffy. U need some way to verify coolant temp, laser temp gun, something. May have other issues causing poor mpg, possibly O2 sensor, any CEL?

 

O2 is new and no CEL or stored codes.

 

gonna try and keep this highjacked thread goin a little longer..
Gonna just replace thermostat tomorrow. (when my heaters on engine temp drops). When my heaters on my aux elec fan will kick on and off seems very random and doesnt matter what engine temp is...any one got this happenin too?

 

Do u possibly have the HVAC controls at a/c or defrost? Both of those positions will engage the compressor and e-fan. Compressor and e-fan on when the selector is in any of the yellow circled positions. It's normal for coolant temp to drop slightly when the heater is in use. U go from 1 radiator shedding heat to 2, when heater is on.

 

i not sure what HVAC control is...I replaced termostat and now when stopped it sit at 210 which it never did before and also has hardly any coolent flow in upper hose untill i give it gas. Even tho its not that cold today on the highway temp was still down with heat on. Water pumps not leaking and i had belt loose and checked all the pullys and they seamed fine. Think it could be waterpump anyways?

 

Heat, Ventilation & Air Conditioning (HVAC). The pic I posted. If u have no idea how old the water pump is (or any other cooling system components), replace them.

 

89 Cherokee, Auto, 4x4, 4.0L.
I am experiencing this similar problem. Temp guage reads about 150*. I used to run about 200* year round. The heater blows hot air.
If the thermostat were stuck closed, the temp guage would read super hot and the engine would blow up right?
If the thermostat is stuck open, the temp would slowly but eventually reach operating temperature wouldn't it?
I replaced the Coolant Temp Sender and there was no change in the guage. So, maybe the guage is bad? This weekend I will swop out the thermostat and see what happens. If the guage is bad, how does one fix that?

 

The temp gauge won't display correctly if it is malfunctioning.....and it definitely sounds like the gauge/sending unit is malfunctioning....no way the heater can be blowing hot and actual coolant temp be 150-160.....not this time of year.

 

Update:
My Fail-Safe thermostat did indeed fail in the open position. Interesting... I did not overheat. I R&R with a Stant 195* thermostat. Problem fixed. Average Eng Temp 200-210*.

 

What temp do those fail? What caused it to get that hot?