Highway "heat creep" - Running hot on the highway.

[Mudderoy]

We all know how the Jeep Cherokee can have issues with over heating especially in stop and go traffic, but after many modifications I'm having a bit of a different issue. Running hot on the highway. It doesn't over heat, but it gets well above the normal 210.

I'll go into more detail about what I've done and what results I have had but right now I want to talk about another "theory" I have to explain this issue.

I went without my A/C for about a year and a half back in 2004-ish. I just didn't have the money to fix it, assuming that it would cost the typical $1200.

Through some research I found that the typical issue was the "O" rings leaking. Later I found that the "O" rings (on the lines that run to and from the compressor) usually go bad after just 2 or 3 years.

I also found out that Walmart sold some stop leak that tries to make those "O" rings seal.

I figured "what the hell" and tried it. It worked! The compressor doesn't seem to keep as much R12(?) that I put into it, but the A/C works and I get a constant 40 degrees out the central vent! I noticed a few days ago that the A/C unit is really short cycling. Maybe on and off every 15 to 20 seconds. Still maintaining that 40 degrees though.

Yesterday I was driving home in 94 degree air temp, and the damn engine cooling system was running hot, just like it would on the highway (70 mph) but I wasn't doing more than 55, and most of the time it was speeding up or slowing down, stopped, etc...

After getting home I filled up the over flow bottle thinking that perhaps I just needed water in the radiator. I can't remember the last time I've added water to the cooling system!

This morning I popped the radiator cap and the coolant level was full. The over flow bottle still have plenty of water in it. I drove to work. Morning air, much cooler out, no running hot problems.

This early afternoon I headed home. After a while the coolant temp started to rise above 210 and then stopped at the same level it was yesterday. About 1/2 way between the 210 hash mark and the next hash mark. OBD II scanner tells me that about 227 degrees.

I know from past experience that turning off the A/C will allow the temp to drop but not usually back to normal while on the highway. I thought I'd give it a try now. After about 10 minutes it the coolant temp was down just below 210 on the gauge, normal.

I've suspected that my failure to properly repair my A/C may be either the cause, or one of the causes of my running hot on the highway.

Logically I thought that if the A/C compressor is short cycling that the condenser (in the radiator air flow) would actually be cooler and not hotter. I am starting to doubt this is true. I mean either the A/C isn't causing the problem and the heat on the condenser is just enough to move the cooling systems ability to keep the temp with in the 210 area, or the condenser is actually getting hotter and that additional heat is being passed to the radiator pushing the temp outside the range that the cooling system can handle.

[4.3LXJ]

Tony

Running AC will always put a strain on the cooling system. After all, instead of 94° air hitting the radiator, the air is more like 124° because the air is cooling the hot refrigerant. The short cycling is normal, and if anything indicates you might of over charged it a little. The car AC is not like your house AC that is designed to run at a constant compressor speed. Car AC has to account for a variable speed compressor so the compressor is a little oversized to start with and has a high pressure limit switch on it to shut it off when there is enough liquid refrigerant to operate properly. If it was constantly running, it would indicate it was undercharged.

[prerunner1982]

I have a theory....what ever is causing your heat problem....is causing your low mpg problem as well.

Proof... none. Just a thought.

[Mudderoy]

Tony

Running AC will always put a strain on the cooling system. After all, instead of 94° air hitting the radiator, the air is more like 124° because the air is cooling the hot refrigerant. The short cycling is normal, and if anything indicates you might of over charged it a little. The car AC is not like your house AC that is designed to run at a constant compressor speed. Car AC has to account for a variable speed compressor so the compressor is a little oversized to start with and has a high pressure limit switch on it to shut it off when there is enough liquid refrigerant to operate properly. If it was constantly running, it would indicate it was undercharged.

What I have noticed is it short cycles and then stops coming on. Then I recharge the system and the compressor stays on for much longer.

[jccatt]

Check the thermostate

[Mudderoy]

Here's another direction I went originally. Transmission heating due to larger heaver tires. I added a 13k BTU transmission cooler. It did not solve the heat creep issue.

I uninstalled the B&M transmission cooler because I had a pretty bad leak. I wasn't sure what the issue was. After removing it I found that the hose clamps were lose, I still don't know why. My intent was to reinstall before summer returned. With the cooler out, I have been seeing the heat creep at lower RPMs, as in the drive home.

I'm going to re-install the transmission cooler tonight after I get home from work and then we'll see if that fixes the heat creep driving home in the afternoon.

I have ordered the B&M transmission temp gauge. I'm going to wire and plumb that in and I'll be able to see a correlation between the highway heat creep and transmission fluid temps.

Once installed and I see where the transmission fluid temps are I'll bypass the radiator. This will remove the additional heat load the transmission is putting on the radiator and the engine cooling system.

I don't want the transmission fluid getting to hot, or too cold. I'm still looking into it but my preference would be to put in a bypass valve so I can manually select the transmission fluid goes through or doesn't go through the radiator.

I've been assured that bypassing the radiator won't hurt my transmission, but I know how expensive it is to have rebuilt, so I haven't bypassed it until I was able to monitor the fluid temp.

I found this interesting post on CherokeeForum.com...


As for cooling, I find my water temp stablized about 210 and doesn't climb as fast under load like it did before. It will still hit the 219 mark which turns on the electric fan and cools down faily quick, since the tranny fluid doesn't go thru the radiator.

:link: (http://www.cherokeeforum.com/f2/bypassing-radiator-only-b-m-tranny-cooler-13893/)

[LizardRunner]

the B&M transmission cooler should take care of all your tranny fluid cooling needs, with or without the stock, in the radiator unit. After all that cooler was designed for street hot rods and those don't usually have an in the radiator tranny cooler.

[Mudderoy]

the B&M transmission cooler should take care of all your tranny fluid cooling needs, with or without the stock, in the radiator unit. After all that cooler was designed for street hot rods and those don't usually have an in the radiator tranny cooler.

Well they come in several BTU ratings. How many BTUs of cooling do I need for my AW4?

[4.3LXJ]

Well they come in several BTU ratings. How many BTUs of cooling do I need for my AW4?

That can be a subject of debate. The BTU ratings as far as I know are for towing on the highway. I used a 10.000 GVW cooler on mine. The tranny will still get warm when wheeling, but not hot. A lot of this subjective process depends on how you use your vehicle. With your use almost exclusively on the highway, the 10K is more than adequate. But I don't think I would go less than that if I was wheeling hard. So in the end, it depends on use.

[Mudderoy]

That can be a subject of debate. The BTU ratings as far as I know are for towing on the highway. I used a 10.000 GVW cooler on mine. The tranny will still get warm when wheeling, but not hot. A lot of this subjective process depends on how you use your vehicle. With your use almost exclusively on the highway, the 10K is more than adequate. But I don't think I would go less than that if I was wheeling hard. So in the end, it depends on use.

Well that is disappointing. Again I go back to the origin of the issue, when I lifted and put the larger tires on. Prior to that the problem wasn't highway heat creep it was stop and go traffic heat creep.

I've ordered the gauge, so we'll see what it tells me and I'll feel safe removing the transmission lines from the radiator with the gauge on there.

[4.3LXJ]

I am not saying you shouldn't run the cooler. I am just saying how they are rated. My opinion is that all XJs should run an aux cooler.

[Mudderoy]

I am not saying you shouldn't run the cooler. I am just saying how they are rated. My opinion is that all XJs should run an aux cooler.

Oh no, I understood that. I was just hoping it was undersized for my application. With the 13k BTU cooler installed, it's actually the 3rd cooler and last one in the chain. The radiator (warmer/cooler), factory cooler, and B&M cooler.

:D

[jccatt]

Interested in the trany guage install Tony. Keen to see how it all go's. Obviously more complex than my t/state option

[4.3LXJ]

Oh no, I understood that. I was just hoping it was undersized for my application. With the 13k BTU cooler installed, it's actually the 3rd cooler and last one in the chain. The radiator (warmer/cooler), factory cooler, and B&M cooler.

:D

So let me see if I understand this. You are going through the radiator first, then the factory cooler and then the B&M?

[Mudderoy]

So let me see if I understand this. You are going through the radiator first, then the factory cooler and then the B&M?

Yes. Problem?

[4.3LXJ]

Yes, as I see it. If you are putting hot oil into the radiator, it will heat the water. If you bypass the radiator, then you will be putting less btus in to it. Use your coolers, the B&M should be enough for the tranny fluid. This should help your problem a little anyway.

[LizardRunner]

X2 a tranny cooler in the radiator doesn't let the radiator do its job to the best of its ablility.

[jccatt]

How come you run through the radiator first? Is that factory?

[Mudderoy]

How come you run through the radiator first? Is that factory?

Well if I'm understanding the direction of the flow correctly it goes from the transmission to the upper part of the radiator, then from the lower part of the radiator it runs to the factory transmission cooler then back to the transmission. I just inserted the B&M transmission cooler between the factory cooler and the transmission.

[jccatt]

Well if I'm understanding the direction of the flow correctly it goes from the transmission to the upper part of the radiator, then from the lower part of the radiator it runs to the factory transmission cooler then back to the transmission. I just inserted the B&M transmission cooler between the factory cooler and the transmission.

Yip yip, with you now.

[Mudderoy]

It has arrived! I ordered it BEFORE I knew I was going to buy the 1999 XJ :(

http://ecx.images-amazon.com/images/I/31xKCKvTerL._SL500_AA300_.jpg

So step one will be to hook this up and run it for a week to see what the transmission temps are. Then I'll add the B&M 13k BTU cooler back into the mix.

[LizardRunner]

will be waiting for that report Tony.

[jccatt]

will be waiting for that report Tony.

X2