Overcooling....engine's too cold

Hi All,

Hope anybody can give me some clues, since I don't understand what's going on.

A while ago my waterpump started leaking. So replaced it and while at it I also replaced the thermostat. Before this operation the XJ was always running 190-200 on the dashgauge, but I did notice that the electric fan was on a lot (probably the pump was already on its way out). After the replacement of pump and t-stat temp's were in the 160-170 range, and I never heard the electric fan again. These temps are too low for my liking though. I burped the car (taking out the temp sensor closest to the firewall) but no change. Then I figured my t-stat was staying open too long. Today I replaced it with a balanced (MrGasket) high-performance t-stat. Just to be sure that would be accurate. Still temps are way low.

Now my next thought is that my temp gauge may be off. Make sense? There are two sensors. One on the t-stat housing and one in the rear of the engine close to the firewall. Which one should I replace? Anyway to check whether it's still functioning ok before replacing? What does the other temp sensor do?

Anyway, this is the story, if anyone has any thoughts please let me know! Thanks!

Tim

What was the rating on the thermostat you put in?

One sensor is for the Computer, while the other is for your gauge. (Can't remember which is which though...)

The sensor at the back of the head is for the temp gauge.

I put in a standard/original 195 degrees thermostat.

So do these temp senors go out a lot? Do they get bad with time? Or is it very unlikely that that is the culprit?

Tim

I'm certainly no expert here, but my best friend is an ASE tech and has worked on a ton of 4.0's over the years. He did tell me that the 4.0's like to run hot (190-220). He also said that a lot of people freak out when they see their temp gauge just short of the red. He assured me that it is very common and that the sender is in the absolute hottest part of the entire engine (right above an exhaust port to boot).

He said that a lot of guys will put gee-whiz cooling systems on their rigs in an attempt to get the gauge reading to come down, -and consequently cause the ECM to freak out and run lots of fuel and cause the things to load up and run like crap.

Senders do go bad, and they're easily replaced.

The one you're after is the one that is on the back of the head back by the firewall, -not the one in the t-stat housing.

I didn't notice what year your rig is, -but maybe you could borrow a scan tool if it's new enough??

Having the "right" thermostat seems to be a big deal on these things as many others have pointed out. I installed a stant 190 on mine and haven't had any issues, but several of the others on here have has issues with the stant and robertshaw units and ended up getting the right one from the dealer and have been happy.

Do let us know what you find out, I'm curious.

If you replace the sender, be sure and get the OEM part from the stealership. Apparently there is some type of calibration between the sender and gauge that you don't get with an aftermarket part. I learned the hard way!

dspilot said:

If you replace the sender, be sure and get the OEM part from the stealership. Apparently there is some type of calibration between the sender and gauge that you don't get with an aftermarket part. I learned the hard way!

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Sorry read this post too late. Stuck in a Nappa sender. Seems to do fine so far. I did notice that when I put in the new sender some air came out, so that may have been the problem too. I decided to stick in the new sender anyways (since I had already bought it) and the temperature reading is now higher: when cruising it's at 170 and when on an incline or stationary it's at around 195. The weather was fairly cold (50-55) so this may not be all bad. Still a little worried about the fluctuation (170-195) but maybe that's normal? When downhill coasting temp would drop to 160.

After all, it may have been the air rather than the sending unit, can't tell. I could of course by putting back the old unit but it's a hassle replacing the unit since I didn't have a long socket and the with the open wrench it took me some time; will get a longer socket this week and put in the old unit next week to check whether or not it was the air or the unit.

So how often should one 'burp' the car?? Are these temps reasonable?

Will report back next week ont the test of the old unit.

Your guage may still be off a little. The t-stat you put in, even though rated at 195*, will allow for more flow and for you to run slightly cooler than an OEM, but you seem to be about 5*-10* too cool. My question is what does your guage say after you've been idling for an extended period (15+ minutes or so after being fully warmed-up) and at moderate ambient temps (60* or so)?

That's good for the aftermarket sender. The one I got from autozone would not even register on the guage.

Crawler said:

Your guage may still be off a little. The t-stat you put in, even though rated at 195*, will allow for more flow and for you to run slightly cooler than an OEM, but you seem to be about 5*-10* too cool. My question is what does your guage say after you've been idling for an extended period (15+ minutes or so after being fully warmed-up) and at moderate ambient temps (60* or so)?

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I tried that yesterday. When I drive it to full warm-up and let it idle, temps will stick around 195. Outside temps were about 50-55. To be honest, I've done the check for about 5-7 minutes, not the whole 15 minutes. Good, bad?

Can do more checks this weekend. It's my wife's dd and she took it out for the week. Although this temp thing is something I don't understand and want to get cleared out, the jeep runs perfect (as it always does:laugh. Sometimes I wonder whether it's not just trying to get some attention:rof:.

Tim

Not long enough. Best if done after fully warmed and driven around. Should raise to at least 210* at that ambient. 70*+ and extended idle should trigger auxiliary fan.

You might also try a laser temp gun to get a better idea of guage accuracy.

Thanks, any advice on where to buy an affordable temp gun? The only ones I've seen so far are $175+. I think that would really be a good way to get a handle on what's going on. At least I would have some sort of verification of the temp.

Tim

Give it a month........try to leave your heater on so the coolant circulates through the heater core too.

Besides what you have burped, there's still probably air in the system. It'll burp itself completely over time.

Lastly have you checked that you did the correct 50/50 coolant/water mix? If you used Prestone you can use their gauge thing to determine your concentration. Good luck!

Blaine B. said:

Give it a month........try to leave your heater on so the coolant circulates through the heater core too.

Besides what you have burped, there's still probably air in the system. It'll burp itself completely over time.

Lastly have you checked that you did the correct 50/50 coolant/water mix? If you used Prestone you can use their gauge thing to determine your concentration. Good luck!

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Thanks Blaine. Didn't know it would take that long to get the air out of the system. Will take it easy and just leave it at that for a while and start fiddling with it in a couple of weeks then.

Tim

Doesn't sound like you are having anymore issues really. Being that cold outside and your still reaching the 195* mark I would say you have it licked.

All I know is it took awhile for my temps to increase back in the winter when I did some cooling system work. But it is still technically winter.....whatever

Ok, I'm back with this. As you guys suggested I've waited a while to let the air out of the system and let it re-normalize. Have driven the XJ now for about 2000 mile and still temps are very low. Too low for my liking. Would have thought that any air would be out now. Here's what I get.

Highway temp ~ 160 degrees
City cruise + uphills ~ 170-180 deg.
extended idle (stationary) ~ increasing temp till about 220 then aux. fan blows it back to about 195 and this is basically repeated every 10-15 mins.

The fact that the temp gauge reads around 220 when the aux fan goes on to me indicates that it's reasonably accurate. Now these variations in temp are too big for me, right? What could it be? From these readings I would think my t-stat just doesn't close (it also takes 5-6 miles to warm up to about 165 in slow city traffic). But I just replaced the t-stat with a high-performance balanced one since the previous one gave me exactly the same problems. I thus believe it must be something else. I thought it was just air in the system, but I can't believe that anymore after burping and waiting 2000 miles.

So,

Can I check whether or not my t-stat closes without taking it out?

I've installed the t-stat the right way around but is there anything else I could have possible done wrong installing it that could cause it to not close properly?

Any other ideas/thoughts what could cause this? (I've run out of ideas)

Thanks,

Tim

Any other ideas/thoughts what could cause this? (I've run out of ideas)


Tim,

Have you taken a good look at your fan clutch? I have a over-cooling issuse too. My fan clutch has lots of resistance hot or cold. The thing should almost free wheel with the engine cold. and have resistance, or be hard to turn by hand when the engine is hot. (motor off on both counts) I just picked up a new fan clutch from a freind and I am waiting for this weather on the east cost to blow over. (It's snowing for heavens sake)

Best of luck to you and take care.

Lee

Pigpen said:

Any other ideas/thoughts what could cause this? (I've run out of ideas)


Tim,

Have you taken a good look at your fan clutch? I have a over-cooling issuse too. My fan clutch has lots of resistance hot or cold. The thing should almost free wheel with the engine cold. and have resistance, or be hard to turn by hand when the engine is hot. (motor off on both counts) I just picked up a new fan clutch from a freind and I am waiting for this weather on the east cost to blow over. (It's snowing for heavens sake)

Best of luck to you and take care.

Lee

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Thanks for the input Lee. Have not checked that yet. Will do. So if the clutch is bad, that would only change matters when the engine is cold right? Or does that also affect long highway cruise temps, after the engine has well warmed up?

Yes if the the clutch is bad. The fan clutch has a wound spring like in an older home thermostat. When things heat up, like ambent underhood temps, the spring should tighten up and the fan should spin faster th give you more air flow through the radiator. If yours is like mine. (1988 SE 4.0 I6 BA 10/5) with the fan tight on the shaft you are overcooling the fluid in the radiator and when the 'stat opens you are dumping the overcooled fluid in to the block. Then the 'stat closed and the process is repeated over and over.

I beleive this is my problem and I will be replacing the clutch this weekend. I will let you know how things go either through this thread or a PM.


Hope this helps.

Lww