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Discussion Starter · #1 ·
So my 175K mile 93 W250 auto, runs awesome now that the fuel pin/3200 spring has been done, fuel screw turn, along with the 5* pump twist. It has as much snot as my wife's 2000 5 speed with a tuner (when it's only on #3)  ;) 

So normal driving 65-70 sometimes 80mph it's at 1/4 on the factory temp gauge even climbing hills at 3/4 throttle. Yes the T-stat is working because I can watch it climb to 1/2 then drop fast when the T-stat opens when I take off in the morning and it's cold.

BUT when I'm hauling my camper or trailer (7K lbs) it goes to the 3/4 mark on the temp gauge. This has me a little worried. And it did this before I did the upgrades.

I am ass-u-meing that the trans is getting hot and heating up the cooling system since I can drive the thing flat to the floor for miles and it never gets but a smidge over the 1/4 mark. The trans is stock, never rebuilt, stock converter with the stock cooling system. It had an auxiliary electric fan cooler BUT it was rotten and I didn't want problems. I have a 3" x 20" trans cooler out of a Mercedes I was thinking about putting into the trans cooling system.

OR is it the rad?

Thoughts please.
 

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mopar65pa said:
So my 175K mile 93 W250 auto, runs awesome now that the fuel pin/3200 spring has been done, fuel screw turn, along with the 5* pump twist. It has as much snot as my wife's 2000 5 speed with a tuner (when it's only on #3) ;)
Off topic, but you might want to look into a dynamic timing spacer from M&H. The dynamic timing spacer will allow for more timing advance without the need to twist the pump. And it's cheap.

So normal driving 65-70 sometimes 80mph it's at 1/4 on the factory temp gauge even climbing hills at 3/4 throttle. Yes the T-stat is working because I can watch it climb to 1/2 then drop fast when the T-stat opens when I take off in the morning and it's cold.

BUT when I'm hauling my camper or trailer (7K lbs) it goes to the 3/4 mark on the temp gauge. This has me a little worried. And it did this before I did the upgrades.
The factory gauge doesn't tell you anything (as mentioned in the other post) I would install a real gauge and find out what the temp actually is, because everything could be completely normal, or it could be a serious problem. Theres no way to tell with the factory gauge.

I am ass-u-meing that the trans is getting hot and heating up the cooling system since I can drive the thing flat to the floor for miles and it never gets but a smudge over the 1/4 mark. The trans is stock, never rebuilt, stock converter with the stock cooling system. It had an auxiliary electric fan cooler BUT it was rotten and I didn't want problems. I have a 3" x 20" trans cooler out of a Mercedes I was thinking about putting into the trans cooling system.
Yes (automatic) transmissions do get hot. Most of the heat created is generated by the torque converter. When you're pulling a load, the tc tends to slip a bit more and more slip equals more heat. The operating temp of the trans is the same as the engine, about 180F*. The trans is either cooled or warmed to operating temp by a heat exchanger (Located under the turbo) which is plumbed to use engine coolant. Under normal conditions the heat exchanger is very effective at maintaining the trans temp. However, there are times when the heat exchanger needs a bit of help to cool, so an air cooled, trans cooler is sometimes provided under the hood.

In those years, Dodge offered an option, known as "Super Cooling" This option provided yet another trans cooler that was located under the bed and featured it's own dedicated fan. So with Super Cooling you had the heat exchanger and two air cooled trans coolers.

The radiator in those trucks was sufficiently sized to maintain both the engine and transmission within their operating temp range. Under loads the temp would go up but the system was supposedly big enough to handle the additional load without overheating.

OR is it the rad?
What you described, sounds normal. But you may want to maintain the system and check coolant and oil levels frequently. A good temp gauge is a must (Better yet is a temp gauge for the engine and another for the trans) and it wouldn't hurt to add in a deep sump transmission pan. If you decide to install the Mercedes cooler, have the trans temp gauge to determine if you're over cooling the ATF when not under load (over cooled is as bad as over heated) You might even want to add in a thermostat and a bypass line

Ed
 

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agreed - if memory serves the factory sweep is a very narrow range - the 3/4 hash mark is not "270 degrees" - it's more in the 210* - you'd need an aftermarket gauge with numbers to confirm but you're probably fine.

The quick way to confirm is grab an IR gun and when it's reading 'hot' pop the hood and laser the thermostat and trans to see how hot they really are.
 

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Here is Mopars answer.

If the fan is like the ones on the magnum engines, you will hear when they kick in, and can watch the temp gauge drop back to the normal spot.
 

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Don't intend to highjack your thread here but I'm curious about the mercedes trans cooler. Is this something that is known to work really well on our trucks..maybe because of the size, reliability, etc.? I will likely be purchasing one but was looking at the aftermarket stuff offered by jegs etc. If it works really well, I will look for (particular model/year?) at the junk yard.
I agree with what was said earlier-the sooner you can get a numerical value on temp you might save yourself from a rebuild or new trans
 

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I think Ed is referring to the 'bed cooler' that AFAIK was a dealer-installed upgrade, and well worth it.  I wasn't aware they were made by Mercedes, but I can confirm they work fantastic.  It's thermostatically activated (don't know at what temps but it'd be a good nugget of info), and when it kicks on it sounds like someone switched on a giant turbo fan under yer butt!...
 

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Mad Max said:
I wasn't aware they were made by Mercedes, but I can confirm they work fantastic.
The OP stated in the opening post, that he acquired a cooler out of a Mercedes.

flyfish said:
Don't intend to highjack your thread here but I'm curious about the mercedes trans cooler. Is this something that is known to work really well on our trucks..maybe because of the size, reliability, etc.? I will likely be purchasing one but was looking at the aftermarket stuff offered by jegs etc. If it works really well, I will look for (particular model/year?) at the junk yard.
I agree with what was said earlier-the sooner you can get a numerical value on temp you might save yourself from a rebuild or new trans
A large trans cooler doesn't hurt, but it would actually work better if you keep the heat exchanger and plumb it in after the heat exchanger.

You might be able to find larger trans coolers sometimes with the fan(s) in a small handful of larger medium duty trucks.

Ed
 

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Derale makes as close to a factory cooler as you will find. Keep in mind the factory was 1/2 inch tubing on the diesels. Very pricey. And those automatic diesels put a TON of heat in the system when pushed. I pull 6000 lb hay wagons at a max speed of 25 mph and have 2 huge hills to get home- With all the slipping from the converter, you can see the temp gauge go up on the hills, and then down just as fast coming down
https://www.summitracing.com/parts/der-15870/overview/
 

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Discussion Starter · #9 ·
The "under bed" trans cooler is what I eliminated because of the rust. Yes it had a fan and was wired into the truck. But it was so rusty I didn't want to chance it blowing out on me. 

The Mercedes trans cooler is actually and oil cooler mounted to the side of the rad on their diesels. I figured I'd flush it out and use that since it has a hi flow rate.

and yes I turn off the O/D when I haul.

I know I need a "real" temp gauge, but as George posted my factory gauge is telling me I'm in the good I guess.
 

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mopar65pa said:
I turn off the O/D when I haul.
man not me - I just watch the trans temps, and if they're same as the engine I just press on. Back when we had our 93 D250 Cummins rig - 300 hp with a DTT converter and deep pan with gauge in the otherwise stock A518 - we hauled our 28' car hauler across country with the cruise set at 70 mph with no problems at all - none.
 

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yup ounce the trans has shifted , and is "in gear" the heat your seeing is caused by converter slippage , if the trans clutches were making the heat , they'd be slipping and burned out really quickly . A good converter is important to the feel , and performance ( ability )  of any automatic . actual oil temps in the pan would be good to know .
 
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