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Topic Review (Newest First)
04-15-2012 08:48 AM

If you aren't familiar with the temperatures that are present in a properly functioning engine, then it is best to do some prepartory work. That way, when you do have a problem, you can diagnose it without any fancy equipment.

Start the engine cold and let it warm up. Place you hands on the various components, EXCEPT THE FAN , as it is warming up. That is the radiator, hoses (radiator and heater), block, area where the sensor is, etc. Make sure to cover the area of the thermostat as it opens. Also, have the radiator cap off and watch the fluid. Before & after the tstat opens, have somone accelerate quickly if there is someone available. Watch the fluid in the radiator to see what it does both before and after tstat opens.

Now you have a base of information for what it should be. When you have a heating problem, you can check it out without fancy equipment, which you likely won't have available, even if you do have them back in your garage.
04-14-2012 11:36 PM
Nicko Hey guys after changing everything And it still "overheated" it occurred to me that it was nit overheating at all. I changer the temp sensor and bam now It works fine. Should have done that first but whatever the rad and waterpump was old anyway. To MntBoy that could very well be the thermostat not opening...just replace it it's about $4 for a new one. If that dost work make sure yor engine temp is actaly ad hot as the gauge indicates...use. Thermal heat gun to determine engine temp. If your engine is really gettig that hot and the thermostat is step is the fan clutch. I that dosnt work check the water pump. warm up the engine with the rad cAp off and rev the engine by hand on the throttle body and watch to current inthe rad...if you see a current chances are your water pump is good. if you see no current the pump could definetly be bad. Ifthat dosnt work next is the rad. Remove it and check to see I it's plugged by running water through it. Other things that can cause an engine to over heat would be a bad radiator cap that dosnt seal. Or collapsing hoses. Hope this helped. Change the cheep simple stuff first. Wish I did that now.
04-13-2012 11:05 AM
overheats only when idling?

In your original post you said it cools down when driving over 20-30. That pretty much rules out the radiator. You can easily check the radiator by taking off the radiator hoses at the engine. Take a garden hose in your hand and hold it to the lower radiator hose. Water should flow out the top hose. If so, your radiator isn't plugged.

You can check the water pump/engine flow by watching the fluid in the top of the radiator. With it idling you should have fluid up to the top of the radiator, to the overflow. Accelerate and the water should drop in the radiator and then rise back up again. That drop is the water being sucked into the engine and the rise back up is it being replaced from the engine. There is a lag there.

That verifies the flow through the engine and through the radiator.

If somebody used dexcool and mixed it with green it can turn to gel in the engine and that is major problem.

It could also be a blocked port back by the temp sensor that only gets enough cooling when the engine is up in rpm.

Sounds like time for a very agressive block flush to me.
04-12-2012 11:37 PM
MntBoy Let us know if it was the radiator...My 01 is doing the same thing...If I turn the heater on when it starts to over heat the temp comes down some.. Does that mean that the thermostat is working properly?
03-31-2012 01:24 PM
Nicko ok so i changed the water pump...and its still overheating! i figured out that the oil in the coolant was nothing but some oil from the chassis when i drained it. seems like a new radiator is my only option right?
03-25-2012 11:06 AM
Nicko I dint put a pin hole but all the air should have come out when I let it run with the cap off. If it's that big a deal I'll take it out and drill a hole in it. I do know that the thermostat wasnt the cause of over I said in a previous post the jeep was running without a t stat. My theory is that the water pumps is out and/or my rad can no longer dissipate heat I'm jut gonna change the pump.

Also the oily film in my coolant...when I drained the jeep after buying it I got the feeling the guy was running dexcool in it so I flushed it and replaced it with green. Could that be the cause of the rainbow of scum in my coolant? I read that it could but I'm no sure. I'm basicly trying to find every excuse to not have to do a head gasket
03-25-2012 06:50 AM
anearthmonkey when you replaced the thermastat did you put the pin hole at the TOP to let out the air in the head? sounds like u still have an air bubble
03-25-2012 12:23 AM
Nubby55 LOL, mine now got oil in Rad. water in oil and run hot if it sits runing, and run hot after a short while on the road. IT'S
Lucky I been getting parts together for a Stroker rebuild.
03-25-2012 12:12 AM
Nicko wow Nubby55! u nailed it! when i originaly bought the jeep it didnt have much coolant in it if was all water, it was full but it was water and now my cooling system looked real rusted im hoping its a coroded water pump. i compleatly removed my radiator ran water through it for a look time and got it as clean as i filled it with viniger and its sitting over night. ill reflush it tomorrow. it seemed like it wasnt clogged at all after i wshed it out.

once again..anyone have any idea what the ranbow film in my antifreeze is? is that really a blown head gasket? alos if it is blown could that be the cause of the overheating? i must admit its a tiny amount of a tiny film.
03-24-2012 11:27 PM
Nubby55 I go with the pump first, there cheap, and no stat mite mean plain water at some time and rusted the pump.
mine does about the same thing but I know I just blew a head gasket, hope you didn't.
03-24-2012 11:27 PM
Xpress My water pump failed and didn't leak one bit. The impeller was corroded pretty badly though, probably from not using the appropriate coolant.
03-24-2012 09:25 PM
Black Bear
Originally Posted by Master4th View Post
Sounds like you eliminated all possiblities, accept water pump and radiator. If it was the water pump you would see it leaking and all kinds of nonsense.

Sounds like it might be time to get a radiator.
what he said
03-24-2012 09:22 PM
Black Bear either way, if the temp is climbing like that and the lower hose is staying cold then the coolant isn't circulating. so I would figure that either the radiator is plugged up or the impeller is wasted in your water pump.
03-24-2012 09:17 PM
Master4th Sounds like you eliminated all possiblities, accept water pump and radiator. If it was the water pump you would see it leaking and all kinds of nonsense.

Sounds like it might be time to get a radiator.
03-24-2012 08:50 PM
Nicko oil looks clean no gunk or anything...and no smoke at all. it runs awesome and smooth when its not stumpted. theres no coolant leakes anywhere on the engine. the thing is tight and dry. should i be worried about the rainbow?
03-24-2012 08:34 PM
jfbilbro what does your oil look like??....and is there any white smoke coming out of the exhaust?.....
03-24-2012 12:37 PM
Nicko So I removed the t-stat housing and to my horror there was no t-stat! So I put the new one in and closed it back up. Topped it off Started the engine and right around 210 the upper rad hose got ik the t-stat works. Buuut the temp just kept rising and the bottom rad hose stayed cold! I think my rad is clogged cause there was allot of rust/grime in the coolant that drained....and I just replaced the coolant last month. Craaaaap The guy who had the jeep befor must have been a compleat idiot. Oh and to make it better the coolant had an oily tinge to it...
03-24-2012 11:30 AM
Master4th Sounds like the Tstat, make sure you put it in a pan of boiling water and test to see if it opens. I've gotten several over the years that didn't work right out of the package.
03-24-2012 10:29 AM
crutch See if you could hook up a temporary gauge and sending unit to see if your gauge, or sending unit is faulty. This happen to me and it was a faulty sending unit at the back of the engine on top of the head.
03-24-2012 09:53 AM
Nicko Wow ballistix thanks for the great info! The shroud is on but covers half the fm blade (the half clossest to the rad). Also when I start I up and idle it, I watched the temp gauge climb past 195 210 240 till never really attempts to come down. That's why I'm thinking the T-stat maybe stuck. But if it is the sensor that means the engine is being cooled properly? Im confused as to the function of the sensor..

Also to answer goldsmith a rad is last resort for me I don't wanna drop 150 on it if it's not nessisary...although it might be who knows. Anyway I'm about to head
to the auto store..
03-24-2012 09:15 AM
hand test

To check the system the old farmer's way, Bring the engine up to temp just before the t-stat opens. Hold the radiator hose loosely just above the t-stat. As the t-stat opens you will feel the temp come up. The hose should get just hot enough that you can't hold it tightly but can if you just hold it loose. After about 30 seconds the temp should go down as the cold radiator water replaces the hot in the engine.

That SHOULD all happen at about 210 degrees. You should see the temp gauge come up to 210, then drop back to about 170 and rise slowly to 210 again. That is, of course, starting with a cold radiator.

If the temp goes above 210 before it drops back then check the radiator hose with your hand and see how hot it is. If it is scalding hot, then the t-stat is opening too late. If it is manageable to hold, then it is likely the sensor.

Also, just a check, is the shroud on? If not, then that would readily explain the problem also.

If you remove the t-stat and want to check it, put it in a pan of water on the stove. Just before the water comes to boil the t-stat should open. You should check the new t-stat the same way. T-stats are infamous for being defective when new.
03-23-2012 10:45 PM
goldsmith I have a 83 CJ 7 258,had over heating problem,chased everything,also have a 89YJ 258 MPI also heating problem chased everything,old school partner came along,and siad throw those radiators away,and go two row aluminum, I'll be damned both jeeps are loving it,cool running. problem solved. Tap water is corrosive,proper 50/50 distilled and coolant,I was quoted here in cali 150.00 to boil them out,same perice as a new radiator. the jury is still out about aluminum,but hey they look good and working fine,so onto my other long list of problems,one down and 33 to go.
Picked up a 73 cj5 304 needs work,radiator looks ugly one more aluminum.
03-23-2012 09:02 PM
Nicko Gonna change the t-stat tomorrow. Hopefully that fixes it. Thanks for a the help guys hopefully I have good new tomorrow!
03-23-2012 07:40 PM
cmoconnell this may help...

How To Find And Fix Common Engine Issues - Jp Magazine
03-23-2012 06:23 PM
Xpress Don't think the temp sender is under a relay?

If the thermostat is older than 5-10 years, or the OEM one, I'd replace it. Same goes for the water pump. There's not a whole lot that can cause these systems to fail and overheat the engine. Did you ever use Radiator Seal? AKA Radiator Perma-Plug.
03-23-2012 05:19 PM
Nicko well theres no leak for sure i looked and looked. when the engine gets to redline honestly it doesn't seem all that hot. the raidiator is never overflowing or smoking....i havent checked the reservior...ill do that next. good point about the t-stat...i just dont know what else to do. i dont have a heat gun to tell if the engine really is 250F maybe it really isint overheating? i have been having some trouble with the relays...could a relay going to the temp sender be bad?
03-23-2012 04:35 PM
jfbilbro would you happen to be leaking any coolant from anywhere on the front of the engine?....If the thermostat was stuck closed it would be running hot all the time..idling and sounds like your water pump might be going out and only circulating the water fast enough when the motor is revved......unless the t'stat is stuck only partially closed/open..try moving the fan from front to back and see it there's any play in's also possible that the sending unit is bad causing false water traveling to the overflow reservoir when it's showing hot? should be able to hear it if it is
03-23-2012 04:13 PM
Nicko changed the fan clutch and its still hitting reline when it idles!
i dont kknow what to do? should i try changing the thermostat?
03-23-2012 01:10 PM
Xpress The fan clutch shouldn't spin more than once when everything is all hot and warmed up. If it repeatedly spins, it's toast.

Doubt it's anything else. BTW, if you do replace the thermostat make sure it has a small pinhole on the flat disk to allow air to bleed out from behind it, otherwise you are going to have a hell of a time bleeding air from the system. The pinhole saves you lots of work an effort.
03-23-2012 11:56 AM
Nicko ok thanks! im gonna change the fan clutch first cause it seems bad. thanks for the info ill let you all know how it goes!
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