Re: transmission temp to cool?
I had a customer drive 30 miles today non-stop @ 60-65mph today to have me check his A/Trans fluid level. It was a 2002 CLK320, they don't have dipsticks. The car was stock, only had a cooler in the radiator.
The ambient temp. today was 57f or so.
While I was measuring, the temp. of the ATF was what I would estimate @ 130f, only warm to the touch.
I do know from experience it takes a loooooong time to get ATF hot under normal driving.
Did you ever try doing a trans service on a truck that just rolled in off the highway? Can you say blisters and 3rd degree burns. I worked for for 15 years at both Ford and Mopar dealers and 5 at a GM shop, mostly only on trucks. We all would dread having to service a drive in customer trans. A passenger car that's been driven in cooler weather and unladen won't gain the temp that a work truck will or one that's been towing a trailer.
It's 34 degrees out here, and I wouldn't think of going outside and trying to touch the transmission pan or bell housing area on my truck after a 20 mile drive. It probably wouldn't burn skin, but I'd be willing to bet that the average person couldn't hold their hand on it. I'd venture to guess that the case temp of that trans is in the 160 -170 degree range or more. A transmission not only makes it's own heat, but being that the case is aluminum, it also absorbs a certain amount of heat from the engine, both from proximity of the exhaust, it's being attached directly to the hot engine block, and the fact that nearly all transmissions are cooled with engine coolant being that the factory cooler normally is inside the radiator tank.
The temp of the fluid can vary depending on where you take the reading. Fluid coming back from the cooler or just being picked up from the pan will be a lot cooler than fluid which has just left the torque converter.
The trans pan itself tends to rid itself of some heat simply due to air flow over it, but at slower speeds and harder driving, this is negligible. There is no substitute for a good cooler as well as the proper rear axle ratio in a tow vehicle.
Supernova is correct that Mopar doesn't use a vane pump, they retained he gear pump design over the years. There are several common problems with the Mopar trans, what I tend to see the most is simply lip seal failures and solenoid failures. Normally a properly rebuilt trans will outlast the OEM trans if a few simple improvements are done.
Having worked on all three major brands, I would say that the best in class would be the GM TH400 and 4L80E trans, then I would say the Ford 4R100, with the Mopar A518/46RE/47RE being at the bottom of the list. The Dodge trans is probably the simplest design, it's more or less just an adaptation of the older 727 three speed. When it comes to the smaller transmissions, GM's 4L60E, Ford's 4R70W, and Dodge's 42RE, the GM and Ford offerings are about equal, with Ford maybe having a bit of an advantage in longevity when towing, but the GM 4L60E may have a slight drivability advantage with a lower first gear ratio. The Dodge 42RE/A500 is just pitifully too light duty. Unfortunately Dodge used the lighter 42RE/A500 trans in most 1/2 ton, Durango, and Dakota trucks as well as many vans up to the D250 class.
I've rebuilt transmissions professionally for years, both in dealers and private shops, they all have their weak points, but some are just poor choices when it comes to owning one as a tow vehicle. I generally prefer Fords, but my Dodge and GMC trucks came to me as part of a business deal, I will run them so long as they are viable vehicles. When I rebuilt the trans in my one ton Dodge van, what I found was a failed intermediate clutch piston seal, broken OD accumulator spring, and slightly burnt direct clutches. An overhaul kit, a couple of new springs, a thorough valve body cleaning, a slight adjustment to boost control pressure a bit, and some new solenoids along with a complete cooler flush and the addition of a super sized RV stacked plate cooler and it should be fine for a long time. I also upgraded to the diesel spec planetary gears and hemi ratio servo lever.
It shifts fast and firm without being harsh, before you couldn't tell when it shifted. A fast shift makes for a cooler trans since it reduces the time which the clutches are slipping or not fully applied between ratios.
Anyhow, back to the question at hand,
As far as a trans being too cold, its not likely ever going to do any damage. There's enough heat in the system regardless of how well you cool it to keep it from running 'cold'. The only 'Cold' situation that would concern me is when running it in sub freezing weather without proper warm up. Once the engine is warm, the trans is too. As far as when to worry, I'd start being slightly concerned at around 200, and worried at say about 230 or so and really concerned if it got there and steadily began to keep climbing upwards. A temporary spike in temp when towing or climbing a hill is normal.
What does your boat weigh? How far are you towing it? How long does it take for it to gain the added temp over normal? Flat or hilly terrain?
I am assuming that you are towing with the OD or towing switch off?
On my Dodge van, I eliminated the factory cooler and am running an over sized stacked plate cooler, I believe it may also be a B&M product. The way I feel is that the added cooling won't hurt since it's a 1 ton truck thats rarely driven without either being loaded or towing a trailer, and a transmission doesn't need the added heat from the coolant or vice versa. It was the right choice in my case, your driving habits and general use may be quite different than mine. My Dodge is a work truck that does double duty as a part time tow vehicle, and I only use it when I need the added size due to it's poor mileage.
