I am working towards replacing the entire cooling system on my 1996 Jeep XJ Sport 4.0L. I just replaced my thermostat housing, thermostat (197*), gasket and coolant sensor and when I start it up and let it warm up, the UltraGauge says 197-199 and the dash gauge shows 220-240. Which one is correct?

Could I have put the thermostat in the block in the wrong orientation? Could I have air in the system? Would this cause the spread on temp readings?

Fix one thing, break another!

I think they still had two senders in 96.
One in the back of the head runs the gauge, one in the thermostat housing or block sends info to the ECU.
The one in the back of the head is going to read higher, and ~20* sounds about right. (my renix block temp is ~175 reported to the ECU while gauge shows 210).

Either way, 240 is pretty hot.

Yes, there are two sensors (coolant in the front and intake temp in the back). The rear one was replaced a week ago and the front one was replaced yesterday. On the UltraGauge it shows the intake temp at 139 +/- and the coolant temp 197-199. Is is possible the gauge on the dash is bad? When I installed my thermostat, it did not have a mark on it as to which way was up. I put it in so the bridge over the sensor was vertical. When I pulled the old one out the thermostat fell out of the housing before I could see which way it was installed (PO had a ton of gorilla snot and no gasket on the housing).

What brand did you use for the replacment sender? I have not found any that match the sensor except Standard brand. The cheapo house brands especially Wells are always high by 20 degrees

It was a BWD sensor from Pep Boys...

http://www.pepboys.com/product/details/8527536/00806


Is this the one you are talking about?

You mean head coolant temp, not intake temp. There is a sender in the intake, but it measures incoming air temp, not coolant.
I think I would pull both senders, throw them in a pot of boiling water and measure resistance on both of them after like 10 mins.

Buy 3/8 and 1/8" pipe plugs first.

The only temp sensors I am aware of are the coolant sensor in the front and intake temp sensor in the back.

Intake air temp, coolant temp (thermostat housing or block), coolant temp (back of head, only runs gauge, 87-96), battery temp (97+), ambient temp (people with ohc).

There are two coolant temperature probes: the two-wire sensor in the thermostat housing is for the computer to tell when engine has warmed up and also to drive the electric fan, and a one-wire sender at the rear of the head on the drivers side that drives the gauge. The gauge sender is a very poor design and fails often. You should replace that with a good part, not a house brand part.



On your 96, your sender is probably a little white plastic connector. edit--looks like Standard has made some more of them



The temperature sensor in the intake manifold is just monitoring air temperature. That is used in conjunction with air pressure from the MAP sensor to calculate air density, which is then used to derive the amount of fuel for the injectors.

Re-reading the op, you were comparing apples and oranges, so that is why the readings are not the same. There's no apparent evidence that you need to replace anything.

This is the rear sensor that was replaced by my mechanic when he put a new valve cover gasket on. I was under the impression it was the intake temp sensor. Either way, both have been replaced. Should I put the old sensor back in the thermostat housing and see if it works better? Nothing was touched on the rear senor when I replaced the thermostat housing, thermostat, coolant sensor and gasket.

Re-reading the op, you were comparing apples and oranges, so that is why the readings are not the same. There's no apparent evidence that you need to replace anything. Can we start over?

My "99" has an analog type temp gauge in the dash and I also have an UltraGauge mounted. The dash shows about 10* different than the UltraGauge, so I used my IR Temp gun for the reading the dash gauge was wrong.


My sensors are the same ones that were in the Jeep when I purchased it 3 yrs ago and I have not cleaned them either. When I replace sensors I buy OEM's as there seem to be a lot of the others even being bad out of the box.

You can use a scanner to get the raw reading from the sensor in the thermostat housing (even works with 91-95 if you have access to a Mopar-capable OBDI scanner). That is how I get mine working--scan the OBDI and watch the gauge, swap parts until I have a sensor and a sender that are close to each other.

Fred, your 99 gauge is fed by the PCM from the sensor in the thermostat housing. The OP has a 96 that still has a separate sender.

I think I was calling the rear sensor that my mechanic replaced the intake temp sensor. Apparently it is a coolant sensor too. If that sensor was working fine and the gauge read normal until after I replaced the front coolant sensor. If the rear one is what the gauge works off of, then why would changing the front sensor out cause the dash gauge to be so high.

Any recommendations on a IR temp gun?

This i my first Jeep and I am learning more and more every day with the help of this forum.

The UltraGauge has reading for coolant and intake temp.