XJ Running HOT? Change your Stat!

[IdahoJeeper]

I've been reading the XJ forum for a couple months now, and taking special interest in the overheating problem that seems to accompany the Cherokee. I've done a radiator flush (which led to a new water pump) and wired in the electric fan over-ride switch in the cab. I've considered going to two electric fans and installing the magnum radiator.

The other day, I did what I'd been thinking about all along - I replaced the thermostat. I didn't go cooler as some have suggested, I put in the 195 stat as recommended by the guy at Schucks. WHAT A DIFFERENCE! I've been told that a stat won't fail closed, but mine had. Now it comes up to temp and stays right around there. I climbed a long slow hill and saw it go up to 205ish but then came right back down.

I'm glad I have the fan over-ride wired in for crawling on those hot summer days, but for normal running, I don't see why we should need all these mods...

[Saudade]

My own experience says if you're runninmg hot, then something's wrong. Fix it and you'll be OK.

Shortly after I bought my '88, the radiator blew. I replaced it. I never noticed until afterwards that it seemed to run pretty hot and I couldn't idle very long without it climbing into the red. A few quick revs of the engine and hold for a few seconds seemed to cool it off OK. There was no problem with the A/C on (elec fan on)

Then one day, my coolant bottle burst. I replaced it with a new one ($$$). After that it seemed to overheat even easier than before. The coolant level seemed OK. I changed the thermostat but it stayed the same.

I then noticed that the elec fan didn't kick in when hot so I assumed the switch was bad. When I removed it, no coolant leaked out of the hole. It was then I realized that I was too low on coolant (likely since the time of the radiator change). Trapped air prevented a proper filling of the system.

I put the old switch back in after testing it (it was OK), and patiently filled the system. After several heat up-cool down-top off cycles, I got the radiator full (really ful). Now the fan kicks in like it's supposed to and even the hottest So Cal days aren't enought to get it over about 220 (more like barely over 210).

True, if I need to change anything in the coolant system, I'll have to purge it again (what a pain), but for now it doesn't seem worth the expense or effort to do it.

[[Fe]weapon]

Little trick for you the next time you have air in your system.
With the engine cold...
Look at the back of the engine right beside the valve cover driver side under all the wires right close to the firewall
there is a single wire attached to a little device that screws into the head this is the second temp sensor(for those that doubt...the temp sensor on the thermostat housing is for the computer, the one i am talking about is for the temp guage). If you remove this sensor then fill up your resevoir bottle air will come out that tiny little hole followed by antifreeze.
once it stops bubbling air replace the sensor and the wire
this should allow all of the air out of the motor, and it will circulate normally without overheating

The electric fan is instructed to turn on by the computer which gets its information from the sensor on the thermostat housing if the motor has an air lock that sensor will be dry and will not heat up enough to tell the computer to turn on the elctric fan

[Xendrea Jasper]

F.Y.I. XJ's run hotter than any other "J" out there. ZJ's, YJ's, WJ's (Durangos) you name it. A little extra cooling doesn't hurt. Ever been to Yuma AZ in august? Not far from So Cal.

[IdahoJeeper]

So just how hot is too hot? I feel better about my XJ cooling system now that I have it functioning at its designed capacity, but I do see the potential for the small XJ cooling system to lose the ability to maintain temp in hot weather. In this case, I can see the need for a three core radiator and hood vents.

When we say we're running hot, just when does that become 'thermo-nuclear meltdown damage causing' hot? Is there a way to trigger the electric fan to come on sooner (automatically), say like a different sensor...?

[Xendrea Jasper]

I thought you wired in an override switch? I like the idea of twin electric. A friend did it to his XJ and it kept the temp more consistant on the trails. Plus there was a "seat of the pants" noticable differance in power. P.S. Thanks for the trick Weapon.

[[Fe]weapon]

Thats true, its so cramped under the hood
the rad is shorter and thinner than a yj
the fan shroud on the mechanical fan side is a joke
and the stock electric fan is a total afterthought
i would overheat in deep snow or mud
I bought two low profile electrics for mine
now the temp guage is right in the middle at all times

btw this is my little cherokee
http://www.irongaming.com/albums/Toys/IMGP0460.jpg

[Saudade]

Sweeeeett!!

[IdahoJeeper]

Meanwhile...so how hot is too hot? I DID wire in the over-ride for the second fan, it just p---es me off that I actually have to reach up and switch it on. When 'weapon' says it runs right in the middle, well, on my gauge that's 210. After all the maintenance and the stat change, mine runs about 190ish until I lean into it on a hill, then it'll hit 205ish. I'm just wondering if I put too much time into staring at the temp gauge if meltdown hot is a lot higher...

[Xendrea Jasper]

4.0L are designed to run (most effecently) at 210 to 215. On the other hand, just because the temp gauge might read 230, doesn't mean your engine is going to grenade. You'll hear "spark knock" when your valves are too hot. Don't get me wrong, if my XJ reaches 230, I'm going to open the hood and grab a Snickers (not going anywhere for a while?).

[IdahoJeeper]

Thanks XJ! It's good to know 215 or so isn't going to leave me stranded on the side of some mountain. I'd like to get past this cooling thing so I can get on to more fun things to throw money at. I still like the idea of dual electric fans, and I've seen some cool hood mods for venting the engine compartment heat that I might do.

In fact, check this site out: http://www.go.jeep-xj.info/index.htm This guy is an Aussie who has some incredible ideas and lots of experience (including a picture of a totaled XJ still on its top). TTFN

[Cam7]

If you have a air lock and cant Burb it drain the fluid and the jack up the front end before filling the rad.Should keep it from forming a air lock.

[Xendrea Jasper]

Idaho, I've been to that web site before. Did you see some of the places that he's been to? He has some awsome pictures of Australa. Talk about a dream vacation: You, your skirt, and your XJ driving on the beach for weeks.

[IdahoJeeper]

OH MY - YOU'VE GOT THAT RIGHT! Yeah, I was really impressed with that guy's site. Lots of info. Looks to me like he pretty much lives in that Jeep. I need to do more living in rather than living under mine!