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Old 03-23-2012, 09:56 AM   #1
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Engine running very hot! help please!

its about 70 degrees today and when i am at a light or in traffic the temp gauge approaches the red and sometimes touches it...but it "cools off" (still way past the half) when im going over 20-30 mph. im worried...any idea what the problem could be? i flushed the cooling system about a month ago and everything seemed fine...

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Old 03-23-2012, 10:18 AM   #2
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Check the fan clutch. Get it up to operating temperature, shut it off then Open the hood and try to turn the fan. It should be very hard to turn, if not it is slipping and needs to be replaced.

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Old 03-23-2012, 10:23 AM   #3
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Check ur thermostat the can get stuck closed and its like 5 bucks for a new one
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Old 03-23-2012, 10:26 AM   #4
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You might also have a bubble in the cooling system. Have you checked your fluid level? It could also be the thermostat.
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Old 03-23-2012, 10:26 AM   #5
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ok cool i check it now!
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Old 03-23-2012, 10:41 AM   #6
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alright so i checked the fan clutch and its real easy to turn when the engine is hot...so im gonna replace it! hopefully that solves it. and i bled the cooling system when i changed the coolant so i doubt there's any air in there..also where is the thermostat located?
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Old 03-23-2012, 10:44 AM   #7
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Should be by ur valve cover two bolts holding it on a hose coming from it to the radiator its the top hose. And that's the housing the thermostat will be inside of it
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Old 03-23-2012, 10:56 AM   #8
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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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Old 03-23-2012, 12:10 PM   #9
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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.
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Old 03-23-2012, 03:13 PM   #10
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changed the fan clutch and its still hitting reline when it idles!
i dont kknow what to do? should i try changing the thermostat?
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Old 03-23-2012, 03:35 PM   #11
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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 running.....it 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 it..it's also possible that the sending unit is bad causing false readings....is water traveling to the overflow reservoir when it's showing hot?...you should be able to hear it if it is
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Old 03-23-2012, 04:19 PM   #12
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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?
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Old 03-23-2012, 05:23 PM   #13
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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.
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Old 03-23-2012, 06:40 PM   #14
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Old 03-23-2012, 08:02 PM   #15
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Gonna change the t-stat tomorrow. Hopefully that fixes it. Thanks for a the help guys hopefully I have good new tomorrow!
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Old 03-23-2012, 09:45 PM   #16
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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.
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Old 03-24-2012, 08:15 AM   #17
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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.
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Old 03-24-2012, 08:53 AM   #18
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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 redline...it 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..
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Old 03-24-2012, 09:29 AM   #19
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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.
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Old 03-24-2012, 10:30 AM   #20
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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.
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Old 03-24-2012, 11:37 AM   #21
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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 hot...so 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...
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Old 03-24-2012, 07:34 PM   #22
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what does your oil look like??....and is there any white smoke coming out of the exhaust?.....
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Old 03-24-2012, 07:50 PM   #23
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oil looks clean no gunk or anything...and no smoke at all. it runs awesome and smooth when its not overheating...im stumpted. theres no coolant leakes anywhere on the engine. the thing is tight and dry. should i be worried about the rainbow?
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Old 03-24-2012, 08:17 PM   #24
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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.
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Old 03-24-2012, 08:22 PM   #25
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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.
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Old 03-24-2012, 08:25 PM   #26
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Quote:
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
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Old 03-24-2012, 10:27 PM   #27
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My water pump failed and didn't leak one bit. The impeller was corroded pretty badly though, probably from not using the appropriate coolant.
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Old 03-24-2012, 10:27 PM   #28
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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.
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Old 03-24-2012, 11:12 PM   #29
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wow Nubby55! u nailed it! when i originaly bought the jeep it didnt have much coolant in it if any...it was all water, it was full but it was water and now my cooling system looked real rusted inside...so 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 possible...now 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 oil...like a tiny film.
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Old 03-24-2012, 11:23 PM   #30
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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
BLOWN!
Lucky I been getting parts together for a Stroker rebuild.

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