Engine/Transmission (1998.5 - 2002) 98.5 autotranny overheats.

[LeeB]

The transmission on my 98/5 overheats when ever I try to pull anything with it. Doesn't even have to be much of a load. Does ok when empty. I have already changed the water pump and thermostat. New cooler and radiator also. Any ideas? I like the truck and want to keep it, but If I can't tow anything with it I might as well have a car.

 

[B.G. Smith]

Is your torque converter locking up when you get up to speed? bg

 

[RustyJC]

I added a large oil-to-air transmission cooler in the hot line of the transmission between the transmission and the radiator cooler on my 1996 3500 V-10/47RE. This truck would experience high transmission and engine coolant temperatures (from the trans fluid dumping its heat to the radiator tank cooler) during low-speed work and steep grades while towing a 36' Jayco Designer 5th wheel (13.5K GVWR) when the torque converter was unlocked and generating TONS of heat from fluid shearing. After installing the oil-to-air cooler in front of of the cooling pack (it mounted on the body bracket holding the hood latch), both transmission fluid and engine coolant temperatures were greatly reduced and became a non-issue.

I think I sourced the cooler from B&M, but I'm not sure all these years later. It's important to get a large cooler with plenty of capacity and lines sized for the 47RE as most off-the-shelf auto parts coolers have smaller fluid lines and can restrict transmission fluid flow besides being a pain to adapt to the 47RE's lines.

Rusty

 

[VolsFan]

RustyJC hit the nail on the head. Had to put a new trans cooler on the 99 and had to end up getting stock replacement from dodge as the parts stores coolers lines were too small. Think it was close to $200 been a few years.

 

[B.G. Smith]

I can see a gas engine needing more cooling. I had a 99 CTD and pulled a 31' fifth wheel coast to coast and only time I had heating problem was when it was brand new and the thermostat came apart. bg

 

[RustyJC]

B.G., the point is that adding the cooler helped cool both the transmission fluid and engine coolant. The latter may not be as much of an issue with the Cummins, but the former certainly is, at least for the OP as it was for me. Unloading some of the transmission fluid heat load from the radiator tank cooler by adding the oil-to-air cooler upstream of the radiator tank cooler is just a bonus for the Cummins-powered trucks as it provides more engine coolant reserve heat load capacity on the long grades, etc.

Rusty

 

[SAndreasen]

There use to be kits on ebay that you could buy to add an extra cooler to the system I think they used a bnm cooler for the kit .

 

[cerberusiam]

Tranmission fluid heat while in lockup should be minimal unless one is WAY overloaded. The older trucks had issues with unlocking the TC at the wrong time, a lockup switch cured that problem.

OP needs to figure out whether the TC is locking and staying locked first to decide what is next. Trying to cool fluid from a non-locking TC in loaded conditions is going to be a waste of time.

 

[LeeB]

It was hunting in and out of lock up in the past until I put a shielded wire on the alternator. I hadn't noticed it any after that, however, this is the only automatic I've driven in many years (I prefer a standard) and may just not be realizing it's not staying locked up. I do switch off the overdrive when pulling a load, but it doesn't seem to help much.

 

[Road Dog]

Lockup only happens in 4th or 3rd with the O/D OFF. Never in 2nd or 1st. My truck has 2 coolers -- one on the front (air to fluid) and one on the passenger side of the block (fluid to fluid). How do you now it's overheating? Is there a separate temp sensor & gauge? Where is the sensor attached? You could have poor flow through the radiators because of a restriction (liking a sticking check ball at the bottom of the radiator).

You could have low pressure inside the transmission (there are ports on the side to check). When the transmission receives a signal to lockup it bypasses the radiator to boost pressure and get faster lockup. If lockup doesn't happen (or if you're cycling lock-unlock-lock-unlock) then things will get hot in a hurry.

 

[cerberusiam]

Try the mystery switch for manhual lockup and validate it is locking the TC when engaged. If you feel it engage and it still heats then you need to look further, possibly plugge dcooler system or other problems.

Unless oyu are grossly overloaded or on a long grade you neve rhave to drop OD once you are up to speed. Given everything is good you tow in OD all day along with no issues. TC locked in OD is going to be the least heat you will see in most cases.

 

[LeeB]

Excuse my ignorance on this one, but please tell me more about the mystery switch. The truck overheats on short but steep grades at low speed, pulling an 18 ft. trailer with 5 round bales. 5000 lb. load including the trailer, max.

 

[cerberusiam]

Define low speeds, 15 mph. 25 mph, 35 mph? Define overheating with a temp. Where are you measuring the temp at?

It is not unusual to see the temps rise dramaticaslly if you are under 40 mph and having give it heavy throttle. The TC is going to unlock in those conditions and 95% of the heat in an auto trans is generated by the TC in fluid coupling. Short spikes to 220-230 degrees is normal in these conditions. If this is towing a load on soft ground off of hard pack roads it is even worse.

If this is at speeds where you can keep it in drive and the TC locked while still having enough power a lockup switch will help, preferably 50 mph or better. If this is happening where you are down in 2nd or 1st gear th eVB will need to be modified to allow a manual TC lock. It will help a lot to be able to lock th eTC in any gear for both heat and power to the ground.

Need to know the exact conditions and temps you are experiencing to know what the next step could be.

 

[LeeB]

I have no temp gauge on the transmission, only the idiot warning. Overheated on a gravel road and low speed. I wasn't driving so can't tell you the exact speed, but certainly under 35 mph and likely under 25. This has happened before and the engine and transmission both overheated. This time the engine temp only showed a slight rise and the transmission overheat light came on according to the wife, who was driving. I was driving my other truck with a much larger load and had no troubles at all, but it is manual transmission. This truck has had overheating issues ever since I bought it, but only when towing at low speeds and generally on a hill. No problems on flat ground and no problems when not towing. Does not drop in and out of OD. Sorry I can't give you better info right now and won't be able to until I get back home next month. Just trying to get some ideas on where to start.

 

[Road Dog]

Low speeds means no airflow over the radiators. My engine barely goes over "normal" so I'd start by making sure the fan clutch is working. At low speeds the transmission is between a rock (the Cummins) and a hard place (a heavy load). If you try to power your way up a hill you'll smoke the transmission. When I'm on gravel and towing I'll use 4-LOW just because I can and the transmission stays cool.

 

[LeeB]

Not sure if she was in 4 high or 4 low, but she was in 4wd. I had told her to use 4 low, but she may have been in 4 high.

 

[JR]

The speeds you are running are the hardest on a transmission when towing because of the TC being unlocked and low/no airflow to keep things cool. The fan will help to a degree but once heat soak sets in it's hard to keep those temps down. Once the light comes on the trans is going to be very hot, the best thing you can do is pull over somewhere safe and put it in neutral and idle the truck up for a few minutes to drop the temps.
If you are running under 25 mph constantly 4low might be an option but you are also now taxing the tansfer case which I don't beleieve is exactly designed for towing. I am guilty of using it occasionally for those same conditions on steep grades. I also have a toggle switch to disrupt the vacuum supply to the CAD so the front axle will not engage, which essentially gives me 2low. This does help the transmission significantly because now you can either lock out OD and the TC will lock in 3rd or allow it to catch OD at low speeds. Either way the TC will lock and allow the transmission to operate much more efficiently.
It's a byproduct of a 4 speed transmission, the gearing is simply spaced to far apart to operate efficiently when hauling heavy loads. The torque of the Cummins helps to make up for the deficit but the transmission takes the brunt of the abuse. It is especially compounded by the too tall gears (in my opinion) if you have 3.55s and/or running oversized tires.

 

[cerberusiam]

As much as a hassle as it is, low range in those conditions is the best thing that can be done. You can actually get the trans to lockup in drive and keep the rpms up enough to keep things cool.

First step would be get a gauge on the cooler output line so you can actually see when you need to modify driving style. The internal sensors are notorious for not being real accurate. Simply choosing the the right gearing may make all the difference. Check the fan also to make sure it is working correctly when things get warm. A bad fan clutch will never allow things to work correctly.

 

[Road Dog]

And one more thing...it doesn't hurt the engine to run near the redline. High RPM and a lower gear will keep the exhaust temperatures down and put less strain on the transmission. The engine is built to run 3,000 rpm all day long.

 

[B.G. Smith]

I think the first thing I would do is check the thermostat since these model years had a history of bad thermostats. The transmission overheating may as some have suggeasted just be a driver unfamiliar with how best to gear up to tow. bg