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Unread 06-06-2011, 09:56 PM   #1
BuckarooBanzai
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1994 YJ Wrangler 
 
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1994 2.5L YJ overheats at high RPM

My 1994 2.5L YJ overheats on the freeway, especially when climbing. I thought it could be the broken bolts/nuts for the exhaust manifold allowing exhaust gasses to affect the temperature sensor. But turning on the heater allows the engine to cool, or at least keep the temperature from rising.

It normally runs below 210 degrees, and this is the only scenario where it overheats. Could exhaust gasses still cause this problem? Is the radiator not doing its job?

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Unread 06-06-2011, 10:08 PM   #2
moonshinefuel
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Tap the palm of your hand on the front of the radiator on different areas after the thermostat opens and it is warmed up. If there are significantly cooler spots, it could be your radiator is clogging.
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Unread 06-07-2011, 06:46 AM   #3
hesserdude07
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just for good measure replace your thermostat... My 2.5 did this when i first got it. I flushed the rad, replaced the t-stat, and then flushed the whole system... Never had another problem. Good luck
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Unread 06-07-2011, 07:07 AM   #4
EABiker
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As mentioned, more than likely a poorly flowing radiator. Give it a good flush, and see if the issue improves or goes away.
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Unread 06-07-2011, 12:52 PM   #5
BuckarooBanzai
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The top of the radiator is warmer than the bottom. In particular, the upper right (passenger side) gets warmer than the lower left.

I noticed antifreeze pooling in a couple of locations at the bottom of the radiator, and a lot of the coils are missing within the rad. I have used BG stop-leak, but that obviously didn't work. Should I flush the cooling system and try more stop-leak? Is the radiator shot?

Also, I will replace the thermostat with the 195-degree version that people recommend.
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Unread 06-07-2011, 01:54 PM   #6
Que89YJ
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1989 YJ Wrangler 
 
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You should never use the stop leak. Its going to hurt the cooling capacity by coating everything inside the cooling system. You need a new radiator. Look up Radiator barn for the best price. Replace the thermostat at the same time. Install a flush kit for $10, it will help you burp the air out afterwards.

One more thought. Check your rad fan clutch. If it is not freewheeling at higher rpms it will block the air flow across the radiator at high speeds. Air movement from any speed above 30 is way more then the cooling fan can supply.
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Unread 06-07-2011, 01:57 PM   #7
Schaef81
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1990 YJ Wrangler 
 
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If as your driving the temperature rises the drops when you take your foot off the gas could be a thermostat stuck open. Just Replace the thermostat and see what happens. What happens is the thermostat is constantly letting coolant flow which means the radiator works double time and cant keep up at higher rpms.
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Unread 06-07-2011, 02:04 PM   #8
SteveJcoYJ
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1991 YJ Wrangler 
 
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if your jeep normally runs under 210 then you do have the 195 degree thermostat already, it shouldnt rise about 210. but start buying doing that first its a 3$ part. If your upper hose is collapsed thats a dead give away of a bad thermostat. Coolant should be flushed out every like 3 years if you have green, 7 if you have dex cool. Deposits build up inside the block, every time you start the motor it can get to a point where your shaking off rust an deposits, and can that can block the waterjackets, radiator ports, an eat away at water pump and thermostat. A radiator is going to be hotter at the top because heat rises, but if its the original an full of rust and missing sections, you probably do need a new one. Last one i bought was from radiator barn an i think i paid 124$ shipped. Before you buy one of those though you should pull off the water pump an make sure it still has a propeller on it an spins freely, lack of flow or slow flow would cause an overheat. check the hoses, and if you havent before you might as well replace them over this project. If you have air bubbles in the coolant thats usually a blown head gasket, or if you have access to a shop then you could put an exhaust analyze over the coolant and check for hydrocarbons. You mentioned exhaust gas earlier, if you have an exhaust or intake leak, a lean condition can cause an over heat. The same for vacuum lines. good luck with it man, hopefully its a thermostat
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Unread 06-07-2011, 02:38 PM   #9
moonshinefuel
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Quote:
Originally Posted by BuckarooBanzai View Post
The top of the radiator is warmer than the bottom. In particular, the upper right (passenger side) gets warmer than the lower left.

I noticed antifreeze pooling in a couple of locations at the bottom of the radiator, and a lot of the coils are missing within the rad. I have used BG stop-leak, but that obviously didn't work. Should I flush the cooling system and try more stop-leak? Is the radiator shot?

Also, I will replace the thermostat with the 195-degree version that people recommend.
Stop leak tends to pool towards the bottom of the core passeges. It is probably the primary source of the clogging. It depends on your financial situation. Best to core it out, or a new one. You probably need a new radiator if stop leak was in there in the first place, it was to address a leak in it, unless it was the heater core leaking, not the radiator. I have a spare new aluminum one, if you were closer i'd give you a heck of a deal on it, seems like you need one. All metal is better, but aluminum/plastic is better than a failing radiator.
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Unread 06-11-2011, 04:00 PM   #10
BuckarooBanzai
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I added the stop-leak after the overheating problem began, and that was to prevent a wisp of steam from tripping the smoke detector. Thank you for pointing out that this is a mistake. It would have been wise to replace the radiator at that point.

I decided the old radiator should be retired. It would appear that the new radiator solved the problem. The fan clutch and all the rest are working correctly.

Thanks to all of you for your advice! I greatly appreciate it!

Last edited by BuckarooBanzai; 06-11-2011 at 04:02 PM.. Reason: I forget stuff.
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exhaust , overheating , radiator , sensor

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