Overheating Questions!!

I have a 2000 XJ that is overheating. Doesn't matter if idling or moving down the highway over 60 just happens faster. Yesterday I was on my way back from CO springs to Wichita, KS when the check gauge light came on and the guage showed it hot. Pulled over and the pressure bottle emptied, as soon as it cooled off enough, I pulled the rad. cap, still full. Filled pressure bottle to full line and continued down the road. It never showed hot and "check guage" light didn't come on but seemed to be at the break pt. But I had to run the heater at full (with the windows down) just to keep it at that pt. Anytime I turned the heater off it would heat up more. My question is, and I hope this doesn't sound stupid, can you overheat with a bad thermostat and still have hot air through the heater. Also it seems as if the upper radiator hose may be overpressurizing and gets very hot, could that just be from bad circulation.

Well, I am thoroughly confused. My '88 Cherokee has a pressure bottle in the cooling system, but your 2000 doesn't -- unless someone modified it. And if your vehicle is overheating, why might you NOT get hot air from the heater?

Step one, IMHO, is to check your radiator in the morning, when the engine is cold. Be sure it is completely full, and that the overflow recovery bottle (not pressure bottle) is half full. Then drive it. See if the level of cooland in the recovery bottle remains the same from day to day.

What temperature does your gauge indicate? XJs are designed to run at 210, so if the needle is pointing right at 210, don't worry.

Either way you need to replace the tstat first as well as the pressure cap, it it overheated bad you damaged it. Then you need to burp the system, get all the air out. Did you notice if the electric fan came on ?? Could also be the fan clutch but at hiway speeds the fans don't really come into play other than to move some air out of the way. I'd check my radiator and see if it's blocked, maybe flush it from the backside with a garden hose. Would not hurt to move the rad back a bit so you can look between the condenser and radiator so see if there is a bunch of stuff that gets sucked up when you get going. Also if the lower hose has ever been replaced make sure that there is a spring inside that hose, you can feel whether it's in there or not just by squeezing it. Use a dealer supplied tstat and gasket and pressure cap. The tstat from the dealer has a small bleed hole, that goes in the 12 O'Clock position when installing. The dealer supplied OEM gasket has the correct seals on it so you don't need to use any cement or other goop. Bleeding the system after this requires about 30 minutes. Just leave the cap off and let it run while keeping the filler neck full till all the air bubbles are out, also fill the overflow bottle to the hot mark. Any addition air should remove itself over several hours of running.
How long and what kind of maintenance has been done on this rig ?? How many miles, engine size, auto or manual, a/c, ps ??

If you have had it since new have you EVER changed the cooling system coolant ??

As you can tell I'm an amatuer auto do-it-yourselfer. Anyway, to give you more info. For the past week leading up to this, I have done exactly what you said, at cool check rad. level and recovery (pardon my ignorance, you are correct) bottle level. Checked again and everything was fine. The temp guage was reading past 210 at the next line, I'm guessing 220 and without the heater on would continue past that line.

my xj does that same crap.

driving on the highway it gets pretty hot and if i stop at a traffic light after being on the hi-way the temp gaugh starts to climb past the 210 mark.

it will heat uo fast in the summertime and never come up to temp in the winter and i'll get horrible gas mileage.

to get it come back down i need to kick on the heat and the defroster the it will fast/slowly come back down.

never had it checked but the thing drinks the antifreeze but the oil looks fine.

I have only owned it for about 3 months, I have flushed it and replaced tstat. But I'm thinking I might need to replace tstat again. Fan works fine, and there are no obstructions in regard to airflow. I'm not real sure about maintenance as far as the cooling system goes before I have owned it. 4.0L, auto, a/c

I have been getting pretty good gas mileage between 18-21 mpg. Also no coolant in the oil.

I have replaced the lower hose and didn't check for a spring, by the way what is the function of the spring.

Rythmguy1 said:

I have replaced the lower hose and didn't check for a spring, by the way what is the function of the spring.

Click to expand...

Keeps the lower hose from collapsing and starving the engine for coolant especially on the hiway or under accleration. If you put in another hose, not dealer supplied and did not move the old spring over to the new hose then you won't have one, most of the over the counter hoses don't, actually none of the over the counter hoses that I know of do, they just seem to make them thicker to compensate but the 4.0L moves ALOT of coolant and vacumn is a wicked thing in a cooling system line...

Best source for hoses is again, dealer, they fit, have the correct sizes, the heater hoses have clamps on them already and the two coolant hoses have the spring in the lower and both have the protector covers already on them.

Can someone expalin to me how running the heater cools the vehicle down. I am confused by that.

your heater blows air through your heater core which is like a little radiator inside your car. The heater core uses the hot coolant from the engine to warm up the air that is blowing past it. Thus giving your warm air.

By warming the air you are transfering the heat from the coolant. Its kind of like having a little radiator.

In addition to being certain that the lower hose has a spring, I also recommend using only a factory thermostat. The factory thermostat has a small check valve in the mounting flange to help avoid air pockets in the system. Although the t-stats sold at the chains have this valve on t-stats for other vehicles, the one they sell for the XJ 4.0L engine does not have it. I have not yet found an aftermarket t-stat with the check valve.

If the thermostat you installed has the valve, the next issue is ... did you install it with the valve in the 12:00 o'clock position?

ok..here's a thought for you...does it get hot sitting still after you first start it in the morning??...1st check the fan clutch, is it moving air??...do you hear the fan whirring and pulling air????, then grab the upper radiator hose..is it hot??..and touch the lower..is it cool or alot cooler than the upper???...change the t-stat..if it doesn't have a bleeder hole in the t-stat then drill one in it...position it at 12o'clock position...now...if it stays cool in the morning at idle then gets hot on the road it's a flow prob most likely, change the radiator and try again..and check or replace the water pump...and check to see when you squeeze the lower hose can you crush it all the way closed??..if so then it doesn't have a spring in it, get a new one from the dealer.....Len

Not to hijack the thread, but is the "check valve" on the Tstat necessary?
I recently changed my Tstat in my 2000 4.0 (somewhere in NM i don't remmember) using NAPA parts. I did another 2K miles going up to CO and then back to houston with no problem. I don't think I'm going to change it since it is not broken, but I will now carry a spare! Dag sure learned that lesson.

I guess i can consult the FSM for the purpose of the check valve.

Tell you what, when the Tstat went bad, for some reason I had little or no coolent in the system. I guess it just evaporated But it seemed like the temp sensor was not in contact with the coolent, b/c all of a sudden as I was driving through this canyon, the gauges would go from normal to melt down red in an instant.

I got that engine HOT. Same engine that I drove 2 miles with no oil.
Still runs like the day I got it (almost)
Cheers, and please enlighten us about the check valve.

Thanks!

the check valve helps purge air out of the system...the reason you were not seeing a reading on the gauges was that the sending unit wasn't touching coolant...so it gets an inaccurate reading...so thats why you need to make sure and get all the air outta the system..Len

Sorry to resurrect such an old thread, but I'm running into a very similar problem with mine. I just changed the water pump and lower hose. Now mine overheats as well. It drives great for about 40 miles on the highway then the heat suddenly skyrockets. I didn't remove any springs from the old hose plus there was a clamp on the outside of the original hose that I didn't swap to the new one either. I didn't pay attn to the positioning of the t-stat within its housing up disassembly or reassembly. I know its not backwards because it didn't fit into the housing one way. Does this sound more like the bleeder hole or a collapsing hose?

Gotta go back to the start, the bleeder hole goes with the hole at 12 O clock. As far as I'm concerned the factory would not put the spring in that lower hose if it wasn't important. One of the reasons I buy my hoses from the dealer, comes with all the clamps and such already on them.
The drives fine for 40 mi is what throws me, normally the 4.0 reaches operating temp after about 10 minutes of either idling or slow driving.
When you replaced the pump did it have the impeller facing the correct direction ?
When it overheats can you see if the lower hose collapsed ? Can you get it to overheat parked in the driveway ? The most important, how did you set the belt tension ?

The belt is set at about where it was before, at least as far as the adjuster bolt goes. I haven't let it sit idling for very long, but the temp will start to climb as soon as I stop, unless I put it in neutral and rev the engine to around 2000. I just may have to call my mom inlaw and tell her not to throw away the old hose and pump so I can compare and snatch the spring and such out it. Either that or just find a Jeep dealer down here and buy a new hose, see if I can return the other new one I just installed. Chalk it up to experience. I haven't checked to see what the lower hose looks like when it gets real hot yet.

I'd suggest picking a krikit II belt tension gauge, about $14 from napa, that will take the guesswork out of the correct tension. The I think it's tight enough or it feels about right or the twist it method does not cut it. That belt new [less than 15 min run time] is set to 190lbs, 170lbs used [more than 15 min run time] and most peoples best guess is closer to 80-100lbs. Also look over the routing of the belt again, it is possible to get it wrong.

I'll check the tension, but the routing's good, I've double-checked that at least 4 or 5 times. If that isn't the solution, then would you recommend the hose?