cherokeeyed

1992 Jeep Cherokee 4.0 Laredo

I just replaced the temp gauge sending unit on the back of the head because mine was broke. The new sending unit is showing the jeep overheating. I took it down the road, not very far but if I accelerated quickly the gauge would drop and at a stand still it would rise?

My clutch fan is good and me electric fan is working. It's maybe 40* where I'm at. There is no shroud on the clutch fan but previous to this when my old unit was working the jeep never overheated... Also was wondering if when I first pulled the old gauge out of the head if there was a chance I could have gotten air in the system.. If so, WHAT'S THE MOST EFFICIENT WAY TO BLEED THE SYSTEM?

djb383

Verify temp with a point-n-shoot infrared temp gun aimed at the t-stat cover. If the efan is running in 40* ambient temp weather, sounds like u may actually be overheating. Efan on temp is 218*. If all is functioning corectly, I can't imagine coolant reaching 218* in 40* ambient. Fan shroud needs to be intact/in place.

tjwalker

You shouldn't have gotten any air in your system by simply swapping temp sending units.

It's not that unusual to get a DOA sensor. I'd suspect that. Where did you buy it?

But verifying with an infrared thermometer is always a good idea.

dukie564

sounds like you have air in the system, or not enough coolant.

cherokeeyed

The E fan is wired up to come on as soon as the ignition is turned on.

I got the sunding unit from Autozone.

The temp gauge is sitting right about 210 now and when going down the road it's etiher on 210 or a knick above 210.

Not jumping quite as high as it was earlier today.

What is the best way to bleed the coolant system?

dukie564

210 is not overheating, that's normal and exactly where the 4.0 likes to be.

Make sure the overflow bottle has fluid in it an drive it a bit - it'll auto bleed any air out

cherokeeyed

It has a 180* thermo in it if I remember correctly back when I did the head I put the 180 back in it.

odgreen

Just because you have a 180 thermostat does not mean it will run 180. It means it opens at 180.
210 is normal operating temp like dukie said.

cherokeeyed

That makes sense. I took it to town and it stayed right around 210, it would move up a little occasionally barely above 210 but never went too far to make me thing it was overheating. I guess these units are pretty sensitive I would imagine.

djb383

Still need to verify coolant temp. Running 30* above the stat rating in 40* ambient (presume u r running the heater as well) doesn't seem right.

Running the efan places extra load on the alternator and again, shouldn't need the efan in 40* weather.

dukie564

that's not how a thermostat works...it doesn't keep the temp below a certain point, it only controls the temp at which the flow gets diverted to the cooling system (ie the minimum operating temperature).

Firestorm500

You should be running a 195* Mopar thermostat.

In any case, your water pump may have corroded fins, making the flow of water less through the radiator.

Your system will self-purge over time.

djb383

If coolant starts getting diverted to the rad at 180*, why would the coolant temp continue to climb another 30* in 40* ambient weather, especially with the heater on thus removing heat from the coolant.

I agree 1000% that the only thing the stat does is, control minimum temp. I doubt anyone here has stated that more than I have. Something ain't right IF coolant temp is actually reaching 210*+, with a properly functioning 180 stat, the heater is being used, in 40* ambient AND the efan is running. I would think in 40* weather with the heater on and the efan on, a 180* stat would be struggling to maintain 180* coolant temp.

All I'm saying is, temp should be verified with a IR temp gun. If the IR gun shows about 180 coolant temp, a 210+ reading on the dash gauge is wacked. If the temp gun shows 210+ using a 180 stat, the heater is on and in 40* ambient weather, then something is wacked in the cooling system.

salad

Absolutely the temp should be verified. As for heat increasing as high with the 180 degree thermostat, well, same question can be posed of the 195 degree thermostat. The whole system is designed for operation at 210 F. The fan clutch is bimetallic and set to run a certain way. If there's not enough heat getting to the clutch, the metal won't deform as much as it should to turn the fan as much as it should. A missing fan shroud would compound this problem as well as impacting performance of the fan when it IS engaged. Also of course the clutch could be shot and slipping too much. So just by running a lower tstat won't do anything if the fan isn't moving more air at a lower temp. This is why low tstats don't work. Well it could be a mislabelled 195 too haha.

Mr. OP, how do you know the fan clutch is good? Is it brand new?

You should have a new fan clutch, 195 Mopar thermostat, and a fan shroud. Anything else is really a hack and will leave you (and us) guessing.

djb383

Even when using a 195* stat, along with the heater, efan running, in 40* weather, I doubt actual 210 coolant would be reached if all cooling system components were in top notch condition. I doubt it would reach actual 210 if the efan was not running and the other operating conditions remained the same. Most all factory temp gauges point to +/- the middle when normal operating temp parameters are met.....Jeep just happens to display 210 in the middle of the gauge.

There r 2 coolant temp numbers referenced in the FSM.....160 minimum and 218 efan on. Nowhere is 210 ever referenced or stated as being normal operating temp. The only place 210 ever appears anywhere is on the factory dash gauge.