Here's a switch...Overcooling problem

Hey folks. I want to get a couple opinions here before I tackle this job. My XJ runs too cold. The gauge barely gets above the 40 celcius reading even when running out on the highway. The interior doesnt heat up at all. Living in the cold north, its important to have a good heater. Could there be any other problems besides the thermostat? The engine is the 4.0L

Air bubble? T-stat stuck open?

8700XJS

My 88 was running to cold, changed the thermostat and it helped. Shortly after, noticed a small seep in the core, that turned into a big seep. Low operating temp. for awhile, then really high operating temp. :flamemad: Changed the radiator, the fins were rotten in a fairly large area, which allowed the seams to split.
Also noticed my temp. fell a little, when my pressure cap started to seep a little.
Also noticed the temp. changed when I cleaned the sealer off of the threads of the sending unit. Also noticed the temp. changed when I cleaned the motor grounds.
Probably the thermostat or the gauge, but loss of coolant can also affect operating temp. Air in the cooling system can affect heater function, but most often causes overheating.

40* C is 104* F ... there's no marking on the factory temp gauge for that, and the dial is not calibrated linearly so you can't interpolate accurately. How are you determining that it's reading (or not exceeding) 40*?

It sounds like a thermostat failure to me. If the thermostat is working, until the coolant reaches the rated temperature the t-stat should remain closed and there is essentially NO cooling. If it were just the gauge giving that reading but you had heat I would say the sender or gauge was bad, or the wire was disconnected at the sender. If you also have no heat, I suspect a thermostat that isn't closing.

After you drive it several miles, does the upper (large) radiator hose get hot ... or even warm?

Mercenary said:

Could there be any other problems besides the thermostat?

Click to expand...

What year is your XJ?
My wifes 97 4.0 wouldn't blow warm air into the cabin and the operating temp seemed a bit low. We changed the t-stat, the problem still persisted. It turned out to be a partial block somewhere in the cooling system. A radiator back flush cured our problem. I'm pretty sure the blockage was in the heater core; we had to change out the radiator last year and the antifreeze looked like crap. (keep in mind, your problem may be different)
Also, Eagle brings up a good point. Check the upper hose.

you may have one of these... but you need a gasket if you change out the t-stat

Ok, I took her for a long spin tonight after letting it warm up a bit. I got in and it was blowing mildly warm air, enough to keep the windows defrosted. Now the Canadian metric guage package goes from 40c upto 130c with 100c right smack in the middle. The gauge was reading just slightly above 40c (estimate 50-60c) I drove for a while and it cooled off until the gauge wasnt even registering (pegged out at 40c) The temp was -7 celcius. The upper rad hose was warm, but not overly warm to the touch.

I guess I will change out that t-stat and see what happens.

Mercenary said:

Ok, I took her for a long spin tonight after letting it warm up a bit. I got in and it was blowing mildly warm air, enough to keep the windows defrosted. Now the Canadian metric guage package goes from 40c upto 130c with 100c right smack in the middle. The gauge was reading just slightly above 40c (estimate 50-60c) I drove for a while and it cooled off until the gauge wasnt even registering (pegged out at 40c) The temp was -7 celcius. The upper rad hose was warm, but not overly warm to the touch.

I guess I will change out that t-stat and see what happens.

Click to expand...

It's the t-stat. My mother-in-laws 95 ZJ did the same thing about a month ago. It was actually broken and the antifreeze looked like sludge. New t-stat, cooling system flush, new anti-freeze and it works great.
Mike Harris

Unless you have a mysterious XJ, like mine, which registers just around the white line which is located to the right of the blue zone.

New thermostat (2), new sending unit, new temp gauge, nothing. The temperature of the antifreeze in the radiator is around 80 degrees Celsius, which is about normal (I guess), the water pipes get hot all right, but the gauge does not want to move to its center position, no matter what I've done.

When I get some time, and the required energy to remove the dashboard again, I plan to run a separate wire from the gauge to the temp sending unit, just to make sure that this is not the culprit. If that fails, then I do not know what else to try.

Casper (the little ghost) is hiding somewhere under my bonnet (or my dashboard).

Rgds
----------
John

I do think you have a thermostat problem but while you have it all apart, you might want to pull the hoses and flush out the heater core. I disconnected my hoses at the engine and let a mixture of coolant flush sit in there for about 10 minutes. I then flushed it multiple times in both directions with a garden hose. You'll be surprised at how much crap comes out of the core and the difference in temperature out of the heater unit. Mine was hot enough that you couldn't keep your hand next to it for more than 5 seconds. I suspect these cores have small passage ways compared to other vehicles as I see a lot of XJs running around with cardboard in front of radiators.

Good luck,
Jay in MA