Pigeon

1998 Xj 4.0, AW4, 231, 152k.

I've had this one for about 6 years, and it's been a solid Jeep. I've flushed the cooling system a couple of times. Last year, it got new water pump, thermostat (Stant 195°), and hoses. It seems to have good flow through the radiator. I have a new Spectra radiator ready when I need it.

Throughout the time I've owned it, engine temperature has been great. It usually runs at or just above the 210° mark. I recently added an aftermarket transmission cooler, in
​​front of the a/c condenser. Since that time, I've observed that it is running a bit warmer. It now runs closer to 220° (95° ambient temperature with air conditioning on).

Yesterday, while doing some mild wheeling, I had the temperature spike several times. Ambient temperature 95°, parked and idling, temperature approximately 220. It then suddenly spiked to around 250°. It did this multiple times. If I began to move the vehicle, or just increased the engine speed, it returned to normal in under a minute.

My first thought was a bad temperature sender, as the temp would suddenly spoke, rather than a gradual rise. I also wonder if my stat may be sticking closed, and causing a spike in temps. I didn't think to verify the temp during the spikes. I did verify the normal operating temp with an IR thermometer. Indicated temp was 220°, as was the top of the thermostat housing.

Any thoughts?

THX-1138

Those are possibilities, but I think increasing temp at a idle usually points to mechanical fan clutch. I'd start there.

CurrySoSpicy

Have you replace the mech fan clutch? Idle and slow speed temp creep screams fan clutch. As the clutch is no long enabling the fan to fully engage the serpentine belts power.

It could be the temp sender. You should confirm the readings with a good IR gun pointed at the t-stat housing to confirm or deny that theory.

In any situation, the fan clutch is a consumable item and if you have never replaced it. It's most likely the original clutch. NAPA makes a great clutch for around 35-40 bucks. Not to bad of job to install either.

There may be other issues at play, but I believe the fan clutch will start you in the right direction.

Pigeon

Thanks for the replies. The fan clutch had been on my list of things to replace. I ordered one from NAPA this morning (272310 the ZJ fan).. I expect that will help with low speed cooling.

CurrySoSpicy

Cool

cclay

Let us know if that helps. I've checked mine when the engine is hot to see if turned too easy compared to cold and it seems ok but.......Hard to tell compared to a new one

CurrySoSpicy

Yea there is no bullet proof method. Sometimes if the clutch is really messed up that method works. But if it's only day like half broken, it's hard to tell.

Pigeon

I have the fan clutch now, and will probably swap it this evening when it gets somewhere south of sweltering here.

cclay

Could you do me a solid and hand spin the old one before you take it off and
the new one after install?

Pigeon

I will, and I'll report the results in this thread.

kerensky

Hmmm, just picked up a new-to-us XJ for my son. Ran a bit hot on the trip home. Thinking this might be a good place to start. Pigeon, lemme know when it cools off up there, 'cause it is pretty sweltering here in Norman, too!

wizardpc

What you are describing is what I like to call the fake-idiot-gauge. I run a scangauge constantly and one of the things I choose to display is engine temp as reported by the ECU.

Your instrument cluster's temp gauge will read mostly-accurately until 210. From 210-235 or so, it will read.....210. At about 240 it will move up a hash mark and you think you're reading 220. At 254, the temp gauge will spike to 260 and your check gauges light will come on. When the temp goes back down to 249, the check gauges light turns off and the temp gauge reports 220.

These are observed results, not guesses. Happened to me last week with a combination of a water pump bearing going bad, 97 degree temperatures, and rushhour traffic.

I suggest that anyone who wants accurate engine temp readings get an ultragauge or one of those $12 bluetooth dongles from amazon with an OBD2 application appropriate for your phone.

The instrument cluster lies to you so that you won't immediately go to a mechanic when temps get to 230 or so, even though you really ought to know when that is happening.