overheating only when i tow???

[muddeprived]

Right back into the 1960's, the factory -- on tow packages and police cars plus other HD -- plumbed the auxiliary cooler downstream of the main cooler in the radiator tank. You are unlikely to "overcool" ever even if:

- The cooler is mounted in the flow of the mechanical engine fan (but not attached to radiator or A/C condenser);

- And a stack-plate cooler with integral bypass is used (B&M RACING) that won't try to cool "cold" fluid.

I would also add a filter downstream of this (such as MAGNEFINE), as

- The factory pan "filter" is really only a screen
- And it's a pain to access, so only the auxiliary filter needs to be changed in the future when changing ATF.

With a temp probe installed in the pan at this time, it's the last for dropping the pan.

On the other hand, bypassing the radiator tank means the ATF is slow to come up to operating temperature, an overall bad idea.

.

Thanks for the heads up on the Magnefine filters. I'm gonna order one.

 

[ParadiseXJ]

...On the other hand, bypassing the radiator tank means the ATF is slow to come up to operating temperature, an overall bad idea...

Sez who??

I have never heard of anyone losing a tranny to over cooling. My XJ gets up to about 110-120 just driving thru town (4 miles)...and on a cool morning, stays that way all the way (22 miles) to work. Oh, and it's a 1990 with 240K+ on the original engine/tranny.

As far as a gauge being a waste of money - meh - to each his/her own.

 

[SuzysJ]

Someone else argued about "overcooling", I don't believe it exists.

And the factory, for nearly 50-years, has plumbed in auxiliary coolers the same way. The ATF needs to be up to op-temp as rapidly as possible (same with engine oil), but, of course, never running any hotter than need be. As the coolant is the first to reach op-temp, having the ATF along for the ride brings it up quickly.

I agree that having a gauge is the way to go.

 

[dieselenthusiast]

Those of us who drive diesel pickup trucks know how important it is to have a transmission gauge. Transmissions are expensive and a gauge is an easy (and affordable) way to monitor trany temps.

 

[Norsk62]

A trans temp gauge is useless. Most of the time the temp sensor is mounted in-line on the fluid return line which does not tell you what the real temperature of your transmission is? Only the fluid returning to it. Which enteres the trasmission behind the clutch packs. Meanwhile your fluid being pumped from the pan is at a hotter temp.

That's why most racing trany's have a bung welded to the front of the pan for a temperature probe for a manual gauge.

One more thing. If you are going to run an external trans cooler, whitch to a manual trans radiator. The cooler mounted inside the auto-trans radiator obstructs the inlet to the water pump, which reduces flow and engine cooling efficentcy. As everyone knows Cherokee radiators are pretty narrow. Because of that, radiators for auto-transmissions simply do not have much room for the cooler. So to avoid cooking the trans, the engineers decided to live with a hotter running engine instead. Which is why 195 to 215 in normal. I got this info from an engineer at Dodge a couple of years ago.

Switching to a exteral coller and manual trans radiator will drop your engine temp to 180 deg under normal conditions and 190 deg towing.

 

[Norsk62]

Sorry for all the type o's

 

[hubs97xj]

Most of the time the temp sensor is mounted in-line on the fluid return line

There's an interesting claim.

 

[Tim_MN]

....avoid cooking the trans, the engineers decided to live with a hotter running engine instead. Which is why 195 to 215 in normal. I got this info from an engineer at Dodge a couple of years ago.

Rather unlikely story.

4.2L CJ Jeeps, 4.0 L Wranglers, and 4.0 L grand Cherokees all use a 195* thermostat.

195* is the temperature that the thermostat begins to open. 200-210* is the normal, dash board gauge indicated, operating temperature for all of the above Jeeps.

 

[Miller88]

ZJ HD fan clutch and a big transmission cooler and you'll be good (provided the rest of the cooling system is up to par!).

Engines last longer, run better and get better mileage running around 210 than they did when they ran cooler temperatures.

 

[Norsk62]

195 deg T-stats are used for optimum fuel emmisions to promote a cleaner burn at a hotter temperature. That has nothing to do with how the engine was disigned or a design oversight by Chrysler.

The hotter enginer temps generated from trans cooler built into the radiator because it obstructs the fluid flow from the radiator. The size of the cooler was a compromise of the minimum to cool the tranny without boiling over. You have to be able to cool a minimal amount of trans fluid in order for it to function properly. Toyota who makes the AW4 used that trany for over 20 years and recommended frequent fluid changes in order the keep particulates in the fluid from burning the clutches.

Also, Toyota auto-trans radiators have a larger built in cooler than Jeep but theres does not obstruct the radiator inlet. The Celica's and Supras ran only a two core radiator under racing conditiions and never overheated. And last, GM's recent serive bulletine states, unless the cooling system is comsuming fluid, the engine is not overheating. With that being said. Temperatures of 220 - 230 deg F are not considered overheating only running hot. Unless you start to comsume fluid by either a mechanical failure or a leak in the system.

This is also why that most guys who are having hot running issue also have automatic transmission over manual transmissions. Go back and read the forums. About 90% autos are running hot under load compared to 10% manual trans.

Another good source is the SAE forums if you know someone who is a member. Have them place a thread. That's what I did and also met with some SAE engineers here in the Seattle area who were also helpful. And yes, if you have not guessed by now, I am also an engineer.

Trust me, go to an external cooler with a manual radiator. You and your tranny will thank me later. The hot setup is to run a big cooler from a Dodge Ram Cummings Turbo Diesel. It is a 6 row cooler with a thermostaically controlled fan mounted to it. Guys have reported temperature drops of 40 - 50 deg f over the 20 - 30 you would get with a B & M super cooler. But here is the best part, it can flow more fluid by volume, meaning it cools more fluid than the B & M.

Jeep did a great job with the 4.0L and it's a shame that it is no longer in production. They took it as far as they could design wise, which is why they have gone to a V6 to replace it.

 

[WB9YZU]

The OBDII 4.0L run at 210 deg F. Not sure about OBDI units. Early XJs ran 195deg. It is a emissions thing. And it's OK.

All automatics that are plumbed though the radiator will dump heat into the cooling system because of heat created in the converter. That's why manuals don't overheat under load, the clutch is a positive coupling device and is not cooled by the radiator. It is not radiator design, but a system design issue, and they all do it.

To reduce heating, reduce the sources of the heat. Tow in 3rd as recommended by the MFG. Do not overload the vehicle. I watch the RPMs. If the difference in RPMs between cruise and maintain are more than 1K, I figure I'm working the converter hard. The harder you work the converter, the hotter the engine temp will read.

And do not expect to tow at 75mph though Nebraska towing a lifted YJ with 33" tires (AKA "Brick", with a lifted XJ with stock gears and the A/C on

Really, this isn't rocket science. It's just being more than a lump of flesh behind the wheel with the stereo blasting your fav tunes.

-Ron