Overheating on fwy?

Hi all, when driving down the road at 60+ my 1995 seems to be getting hot (215-225+). This gets worse with A/C on (in 75 degree weather). When I slow down or am Idling, I stay at 205-212 with the Aux fan varying on and off. Just had the radiator fixed 3 days ago (was cracked and leaking). I am going to replace the T-stat and see if that will help. Had the system burped today but did not seem to help much. I have overgeared to 4.56 (last fall) with 31's and I run in the 2500-3000 rpm range on the fwy - should this matter? So, it is cool when slow but hot when at speed - I can only think of the T-stat or the water pump - any other ideas or am I on target. You would think that it would cool from the air passing over the motor but I dunno.

Thanks in advance,
Phil Hover

My 88 was doing the same thing on the highway, until I replaced the exhaust. I went to Rusty's high flow cat and cat back flowmaster. Not only did it improve all around performance, it also allowed it to run cooler. If your cat or muffler is clogged it is restricting the amount off HOT air your engine expels. Where do you think the majority of the heat your engine produces go???Out the tailpipe. Just a thought this worked for me. Now if I could just get the brakes to stop dragging. Good luck.

WILDHORSE

By the way I am also running between 2500 and 3000 rpms on the highway with 33's in Drive.

This could also be caused by a weak or missing spring in the lower radiator hose. At high RPM there is so much suction that the hose collapses.

Did this start AFTER you had the radiator repaired? If so, then I would back-flush the radiator because it's possible it became partially blocked with loose solder. Definitely check the thermostat.

Erik
88 Comanche

Also, are you running an automatic?

Any chance that you're not getting the TC locked (more throttle opening so the TPS signals the ECU to keep the tranny unlocked -- can test by lifting off of the throttle slightly for a few seconds and seeing if the RPMs drop a few hundred, or by lightly touching the brakes while maintaining speed and see if the RPMs increase by a few hundred) --

related question

Not to steal this thread-- but my fan shroud is all but missing, how much of an impact does that thing make on the freeway?

When my XJ did this( getting hot on the highway) it was just an old clogged up radiator. It was 13 years old anyway so I replaced it.
When I got all the water out of the old 2 core radiator, it was heavier than the new 3 core I was putting in. That's how much crud was in it.

Re: related question

DeathByXJ said:

Not to steal this thread-- but my fan shroud is all but missing, how much of an impact does that thing make on the freeway?

Click to expand...

Not much, because vehicle motion will push ait through the radiator anyway. The shroud makes more of a difference at idle.

"Also, are you running an automatic?
Any chance that you're not getting the TC locked (more throttle opening so the TPS signals the ECU to keep the tranny unlocked -- can test by lifting off of the throttle slightly for a few seconds and seeing if the RPMs drop a few hundred, or by lightly touching the brakes while maintaining speed and see if the RPMs increase by a few hundred) "

Yes, it is a automatic. I am confused by your post - My RPMs DO drop a few hundred after I let off - with some rear driveshaft play - no sye. What does this mean and how do I fix it - "not getting the TC locked more throttle opening so the TPS signals the ECU to keep the tranny unlocked " TC being transfer case? What does it mean for overheating?
Thanks,
Phil

soarprod, my question would be "What changed"?
Sounds to me like the thing that changed was, a leaking radiator repaired. Did you have this problem prior to the repair?
If not I wuld tend to do as DaveWV mentioned and back flush the radiator, as you may just have some crud clogged in there.
As for burping the cooling system in a 95, I would think there is no need, as it is an open system, and should blead itself.
If you did get new hoses, make sure the lower hose does in fact have a spring inside, or you will begin to colapse the hose, and that could create a problem.
On the other hand, you say there is no problem at idle or while driving slow. Hmmmmm. That is when most have a problem with higher temperatures.
That would seem to rule out the radiator, hoses, waterpump, and t-stat.
As for gearing, you should bew able to run all day at 3000RPM, with no problems at all.
It appears something is restricting airflow across the radiator. Perhaps your fan clutch is locked up and not allowing the fan to freewheel at the higher rpm's.
Or perhaps as was posted your torque converter is for some reason not locking up.
Good luck, and be sure to get back with anything you find wrong.

soarprod said:

Yes, it is a automatic. I am confused by your post - My RPMs DO drop a few hundred after I let off - with some rear driveshaft play - no sye. What does this mean and how do I fix it - "not getting the TC locked more throttle opening so the TPS signals the ECU to keep the tranny unlocked " TC being transfer case? What does it mean for overheating?

Click to expand...

Here's an example of acronyms coming back to haunt you. Although "TC" is usually used to indicate "transfer case," in this instance it refers to the "torque converter." You should have a lock-up torque converter, but sometimes the lockup fails and that allows slippage under power. Slippage = friction = heat.

I know at least one person who has had this problem ever since he bought his XJ (used). He wired in a toggle switch and he now controls the lock-up manually.

Eagle said:

Here's an example of acronyms coming back to haunt you. Although "TC" is usually used to indicate "transfer case," in this instance it refers to the "torque converter." You should have a lock-up torque converter, but sometimes the lockup fails and that allows slippage under power. Slippage = friction = heat.

I know at least one person who has had this problem ever since he bought his XJ (used). He wired in a toggle switch and he now controls the lock-up manually.

Click to expand...

when exactly is it supposed to "lock up".

If I install a switch I want to know the correct time to lock the TC.

How do you lock up the torque converter? Can something be replaced so that the tranny doesn’t unlock? Any help is appreciated.

i to have this problem in my 90 when i went to replace my t-stat there was no old one why do people do that anyway i put in a new one also new hoses without the spring in the lower one but will be fixing thatand my electric fan did not work so i wired it to a toggle switch now at idle it runs like 170-180 degres on the highway the faster i go the hotter it gets and i know this is not really hot but it gets up to 200-205 degres and if i turn off the electric fan it will over heat at idle i was thinking new radiator or water pump what do you think

Over heating at idle usually indicates that the viscous clutch on the primary (mechanical) fan is not working.

put the spring back in the lower radiator hose but havent go on highway yet around town is less then 190 degres so thats good