[tatehill]

Hey guys, I have searched through the forum, and couldn't quite find anything that fit what I'm having going on. Ok, Last week I replaced the Rad and waterpump because I developed a leak and the factory rad was rusted out, so I got a 3 row brass one, decided to replace the water pump as well, and I flushed the system completely out as the water was a pure rust color. All that went in without a hitch.
Then the problem...I had to drive out to a friends house during lunch a few days ago, and it's hot here in AR right now, so I left the Jeep running in the drive with the a/c running. I was in the house for about 20 mins or so, and I came back out it the temp guage was reading 260!! So I got in and drove it and it cooled down back to normal temp and stayed there. So I read out here and thought...it's my thermostat. I went to the Local Jeep dealer, got another one, put it in...no problem. I decided to let my Jeep idle in the drive for 40 mins w/ the a/c on and outside air temp was about 104, and the jeep never got about 210 (which is where it is normally). I was like, yahtzee! It's fixed! Well I wanted to drive it to make sure. So later in the day my wife and I ran some errands (about 10 miles away on interstate) she went in the store and I stayed out while the Jeep was idling...about 15 mins out there...it started to climb again and got to about 240 and then I started driving around to cool it back off.
I am desperate now to figure out what the deal is...and I don't have anymore tests that i know to perform. It seems like it is only overheating on idle and only after I drive it a short distance. Anyone else out there with the same issues or ideas?
Thanks in advance!

[superjoe]

i would say fan clutch it is not kicking on to help cool the motor down.

[atomicmoose]

Either the fan or...

Did you burp the air out of the system when you replaced all the fluid?

[tatehill]

I did burp the system to get the air out. The flush kit I installed has an air valve that will allow the system to get the air out and I also ran it on an incline while the cap was off to get the air out.
Ok, the fan...it will not rotate but about 7 inches if I turn it by hand (i.e. it has that much resistance on it). I thought that was how you checked it. Is there another test that I can do to check it?
Another thought, about 2 months ago, for about a week, there was a rattle underneath it when I killed the engine. I believe it was the Cat Converter. Ok, now it doesn't rattle anymore. Could that be building up pressure while I'm driving and cause it to overheat, and not when I don't drive it anywhere? I would think that it would do the same even if I just let it idle in the driveway and not going anywhere.
Thanks again guys all this helps!

[Jeeples]

A 3 core radiator?


That might be part of the problem right there. If your fan clutch is not up to par, or if at low RPM's your fan does not move enough CFM to properly cool all that extra coolant, then that would cause overheating.

Usually 3 cores are better suited to prolonged amounts of freeway travel or towing. Most people don't recommend something that large for low speed applications.

Also, as you sure the Jeep is actually overheating? You might wanna get a digital thermometer and make sure your gauge isn't reading funny.

[atomicmoose]

A clogged cat can cause heat issues.

Try saying that five times fast.

[tatehill]

Well if the rad is too big for the application, then wouldn't it overheat while I am idling...whether or not I drove it before hand?

What's the best way to check the fan clutch to see if it's working properly?

Also, are there any tests to check if the "Cat converter is clogged"?

[noflacko]

Yes, a clogged cat can cause some overheating. We were lucky, our 94 YJ's cat actually started to come apart! Call the dealer (yes, the dealer) and have them check your VIN against a recall sheet, or try this link: http://www.jeep.com/webselfservice/jeep/index.jsp?screenName=recall


We got a free cat install on a 13 yr old Wrangler! Maybe they charged us for brackets or partial labor or something like that! Not free, but very, very cheap!

[laybackman]

Originally Posted by tatehill

Well if the rad is too big for the application, then wouldn't it overheat while I am idling...whether or not I drove it before hand?

What's the best way to check the fan clutch to see if it's working properly?

Also, are there any tests to check if the "Cat converter is clogged"?

Fan clutch should provide resistance when the vehicle has been run for some thirty minutes or so. If bad they spin rather easy. Did you reinstall the fan shroud? If not that is your problem for sure, assuming your system is full with a 50/50 mix. And there are no other issues like advanced timing or a lean fuel mixture. A clogged cat could cause overheating but you would also have performance issues also.

[yjdrvr]

i agree about the fan but what about your water pump impeler, you could have the wrong number of blades or at the wrong angle,,,i would say compare it to the factory one you took out. maybe check for gaps as well, maybe it's not pushing enough coolant, which would be why it is overheating at idle. and try a 180 or maybe 195 therm. and i highly doubt it is the cat if its overheating at idle

[joe's_yj]

have you tried reverse flushing it? sometimes thats the only way to get a clog out.

[Jeeples]

Originally Posted by yjdrvr

i agree about the fan but what about your water pump impeler, you could have the wrong number of blades or at the wrong angle,,,i would say compare it to the factory one you took out. maybe check for gaps as well, maybe it's not pushing enough coolant, which would be why it is overheating at idle. and try a 180 or maybe 195 therm. and i highly doubt it is the cat if its overheating at idle

That is highly unlikely, however it is possible that perhaps the rotation of the impeller is incorrect, which has been known to happen before.

Also, the thermostat does not regulate how hot the engine runs, but rather how quickly it warms up. Changing to a colder thermostat can be detrimental to performance and MPG as well.


As far as the running hot while idling, it's possible that it will not overheat when just idling. When you run an engine hard it obviously creates excess heat, if your heat exchanger (in this case, your radiator) does not have enough air passing through it, the excess heat cannot be shed and the overheating condition can occur.

However if your engine is just idling, it's not going to generate a lot of excess heat that your cooling system cannot handle, which means that under these conditions you will not experience any overheating.

Again, this is just a thought, since mechanically it seems that everything is up to par. You may search the TJ section as 3 core radiators are discussed in more detail there then the YJ section.

I still think you should invest in a digital thermometer and see if your gauge is accurate.

[laybackman]

Did I read that the thermostat does not control engine temps? If not then what does? Mis-information is as bad as no information.

Your thermostat is the major component used to control how hot or cold your engine runs at. Your radiator is also sized for your engine thats why they come in different sizes also. BUT the thermostat controls water flow which is most important in the heating/cooling process so....
1.) They come in different temperature ranges to control engine temperature, and they do nothing else.
2.) If it opens up too much, (and they can), you will not get to proper running temprature in cooler weather and you will get very little or no heat. In addition not getting into closed loop mode will detune an engine real quick.
3.) If it fails to open you end up on the side of the road.

[yjdrvr]

Originally Posted by Jeeples

Also, the thermostat does not regulate how hot the engine runs, but rather how quickly it warms up. Changing to a colder thermostat can be detrimental to performance and MPG as well.

im sorry but that is wrong, although the therm does regulate how fast it warms up that it is the key component in reguolating engine temp. by allowing a certain amount of coolant in.........so i would go by yourself the stock therm. and check your water pump compared to stock and see if that could be the problem

[pmeguy]

My YJ doesn't have A/C but every car I know of that does has the condenser coil in front of the radiator. If the air flow is being blocked by a dirty/damaged condenser coil, a short drive followed by a long idle could easily cause an overtemp.

One more thing to investigate.

Good luck!