Engine temp question

[rworks]

OK, I know the 4.0L takes a little time to heat up, but this is ridiculous.

 

It was about 45-50 degrees out yesterday and I drove 30 miles at about 50mph one way and then 30 miles back home. In that whole time, the temp gauge never got above 120. I know its not the temp sensor, since a) its 3 months old and B) it sure seems to work fine when its 80+ out.

 

So is there a problem here or what?

[jtdesigns]

My truck is doing the same thing... I think the heater core is flowing badly. It still isnt running at 210 like it should.. more like 160 to 180...

I'll add to this...

I believe I have my cooling system in tip top shape. I thought I had a good flush through, but now the temps have fallen I think I should do another flush. My heater gets warm, but not like what I think it should, but then again the temp gauge does represent a lower temp.. Maybe the Stat thermo is opening too much, or my truck is running really rich.. I'm going to do a acidic flush this week end and see if it improves the heater/cooling. It seems like the truck isnt getting HOT, HOT, HOT, but only luke warm.. The only reason I noticed it, was because of the heater.

[BLHTAZ]

I wouldn't trust the guage...get a laser thermometer and check to engine to see what it is really running at. It's just not possible for it to run at 120. I think there is a problem with your guage.

 

If you are not getting heat from the heater, then I would agree with JT that there is likely a flow problem somewhere whether it's in the heater core or not.

 

I don't even have the heater core hooked up in my truck...but the AC works well ;) (it leaks and I don't want to rip the dash out)

[Randy in Maine]

Thermostat.

[mjtjnj]

Thermostat.

:agree:

[fiatslug87]

How can it be the thermostat? Even if the thermostat was stuck open, after 30 miles at 50 MPH in 45°F weather (not very cold) I would imagine the temp would be up at the 210°F operating temperature.

 

On a related note: Will a temp sensor for an '88 yield accurate temperature if it's feeding a gauge out of an '86?

[Randy in Maine]

In that whole time, the temp gauge never got above 120.

 

Also make sure the antifreeze is a 50/50 mix.

[Eagle]

How can it be the thermostat? Even if the thermostat was stuck open, after 30 miles at 50 MPH in 45°F weather (not very cold) I would imagine the temp would be up at the 210°F operating temperature.

You would imagine wrong.

 

The purpose of a thermostat is to keep the temperature UP. The way it does that is by closing when the temperature drops below the range for that particular thermostat. Once the coolant temperature rises again, the t-stat opens. If you ran 30 miles at 50 MPH with no thermostat, I doubt your operating temperature would ever get high enough to even put the ECU into closed-loop mode.

 

On a related note: Will a temp sensor for an '88 yield accurate temperature if it's feeding a gauge out of an '86?

Yes.

 

There are three possibilities here. The sender is one, and the fact it's new does NOT mean that you can believe it's accurate. Second is the gauge itself. Third is wiring. The temperature gauge in my '88 XJ has been riding just above the first tick mark on the gauge for about five years now (whatever temp that corresponds to). But I have good heat. And my gas gauge and voltmeter have also been reading low, for about the same period of time. I'm fairly certain it's because of corrosion/oxidation where the cluster grounds to the chassis, but I know where they normally run so it's not a big deal. As long as I have a needle that I can see if it's NOT where it normally sits, it's okay. (Not ideal, but "okay.")

[mvusse]

Heck even when it was 14 degrees (-10 Celsius) Tuesday morning I had warm air come out of my defrost vents before I had driven a mile (1.6 km).

 

I'm guessing thermostat stuck open, but a quick (temporary) fix would be to stick a piece of cardboard between the grill and radiator.

[FxRacing282]

How can it be the thermostat? Even if the thermostat was stuck open, after 30 miles at 50 MPH in 45°F weather (not very cold) I would imagine the temp would be up at the 210°F operating temperature.

You would imagine wrong.

 

The purpose of a thermostat is to keep the temperature UP. The way it does that is by closing when the temperature drops below the range for that particular thermostat. Once the coolant temperature rises again, the t-stat opens. If you ran 30 miles at 50 MPH with no thermostat, I doubt your operating temperature would ever get high enough to even put the ECU into closed-loop mode.

 

On a related note: Will a temp sensor for an '88 yield accurate temperature if it's feeding a gauge out of an '86?

Yes.

 

There are three possibilities here. The sender is one, and the fact it's new does NOT mean that you can believe it's accurate. Second is the gauge itself. Third is wiring. The temperature gauge in my '88 XJ has been riding just above the first tick mark on the gauge for about five years now (whatever temp that corresponds to). But I have good heat. And my gas gauge and voltmeter have also been reading low, for about the same period of time. I'm fairly certain it's because of corrosion/oxidation where the cluster grounds to the chassis, but I know where they normally run so it's not a big deal. As long as I have a needle that I can see if it's NOT where it normally sits, it's okay. (Not ideal, but "okay.")

:agree: a t-stat is cheap replace it and your problem should be gone.