Drove yesterday with over 1000lb load down hilly highway triyng to go as close to 55 mph as i could -- not easy in a NA. The gauge eventually hit 160 and didnt go over it. When it was at 160 I hit the freeway and did over 60 and 70 for 11 miles. It got to about 180 when I pushed 70.

Today, I drove for an hour with 2 barrels of Biodiesel -- about 800 lbs i would say. I went 55 and the gauge did get over 160. After I dropped the barrels off and drove with an unloaded trailer, I went faster -- 65 and 75 for another hour. Temp hit about 175 .

So, it seems driving fast is what heats up the trans and the existing cooler works pretty good.

In a stroke of pure genius I finally verified that the left cooler line is the return from the cooler. I started her up cold and drove a little and felt at the pan which banjo bolt was hotter. The right one was

Now, we know that the cooler returns oil that is 160F pulling a load or not and that the faster you drive the hotter your trans gets. How close is that cooled temp to what the transmission is operating with? Would it be desireable to have more cooling that that? I still have that auxillary cooler I am curious about. But not sure I am curious enough to spend the 50.00 on it or the time to install it. But I will if people think it woud be beneficial.

I'm curious about the transmission cooler also acting as a heater. Interesting concept. Is this really true?

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

Yes it is true. Some OE engine oil coolers use a thermostat to control when engine oil goes out to the cooler.

i think the original person who mentioned tranny cooler as heater was referring to the original equipment cooling section in the bottom of the radiator. if the engine warms up quicker than the tranny, which perhaps usually it does, then it will serve as a warmer to the tranny til the tranny fluid gets warmer than the coolant, after which it acts as a tranny cooler.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I like your methodical approach to testing. From what you have seen, a couple of questions arise.

First, what were the outside air temps? and coolant temps? This will be one of the major factors as to what time of the year you will be towing the camper trailer.

Second, how long or what distance did it take to reach the higher recorded temps with/without a load? And how does this relate to your speeds?

As you are finding out, heat is your biggest factor in towing. Some put all of their focus on power. A friend of mine found this out the hard way when he put a V8 in a mini-pickup and tried to tow a boat trailer, which resulted in a cooked tranny. You can pull with a 4 cyl. if the cooling system is sufficient.

If you plan on hot weather, extended trips, I would still recommend the aux. tranny cooler + fan. The fan will be a precaution for a situation where you might be caught in stop-n-go traffic after highway speeds.

(Maybe the reason the instructions say to install the temp guage in the return line is the "sell factor" of how efficient their cooler is. I would want to know the temp of the fluid coming out of the tranny as it is my concern.)

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Sam

84 300SD 350K+ miles ( Blue Belle )

Glad to have the interest Here is a fuller report --

So far the outside temp ranges were from 55 and rainy to 85 and sunny. When i pulled the trailers it was in the 80s. The tranny may heat up faster pulling a load however not much. This is probably because I drove much slower with the load. Speed and hill climbing and hot weather seems to be the thing that heats it up past 160F load or no load.

Pulling a 1000 lb load down a hilly highway or on the interstate at 40-65mph it took approximately a good 30-40 minutes , 20 - 30 miles drive in 80F weather to get it up to 160 where it hovered for 30 more minutes. When I dropped the load and drove 70 and 75, the temp went up to 175 or 180F.

City driving it takes longer to heat up and never does when just running errands all day. Resting even for just five minutes cools it off significantly -- like 30 degrees on the gauge for what that is worth. It took a 5 miles on the interstate to get back up to 160 pulling the trailer after a quick pitstop.

Overheating on this B&N gauge starts at 220F. Between 220F and 260F it is yellow (caution) and after 260F it becomes red. They tell you to install it on the return line. Since they make equipment and coolers for race cars I'm trusting thier judment and concluding that so far, the built in tranny cooler works plenty good. In heat of summer or if I need to climb the Rockies, I may need more cooling.

On a rainy day, driving slow across town, lots of water on the roads, driving for 1 hour, tranny never broke 100F. Could Seattle trannys be the best ? But is it good to get the oil to operating temp of 160F ? Dont know. To me, it seems that tranny fuid is so much less viscous than engine oil that it does not need to heat up to flow. However, the question is what is the ideal operating temp for tranny fluid.

If you do an Italian tuneup, do it soon after the engine warms up and not after a long highway drive as your tranny oil is hot then and you dont want to heat it more than you have to.

Hills climbing is just like driving fast and stresses the tranny. Pulling the trailer up a big 1 mile hill in "L" with tranny at 165, it climbed to 185. (Aprroximate needle readings mind you ).

The engine heats up a bunch faster than the tranny. My engine runs at 85 to 90C ( 185F - 194F) after 10 minutes. The tranny only ever gets that hot under severe load and after an hour driiving. This could indicate a few things --
1) The coolant does not heat up tranny fluid very fast
2) There is a thermostat in the tranny cooler I'm not aware of that is malfunctioning.
3) One of my gauges could be a few degress off and they really are at the same temp.

I'm curious to bypass the cooler and see what temps are. Also curious to install the little aftermarket cooler I got and see if it cools more and if the oil heats up slower. And then to put the stock back in and have both running and observe. Not sure this will happen soon though.

All tests were done with new flluid and filter. I lost a gallon of fluid putting in gauge in line.

I think that is about it.
To take care of your tranny --
1) Dont drive too fast all the time and take breaks on long drives.
You can tow and not over heat your tranny. You have a nice built in cooler already and dont need and aftermarket one. If you tow a really heavy load try to do it on a rainy day or in the winter You can grab the lines at the tranny pan or cooler to see how fast your fluid is heating up or see if you need to give it a rest. At 160 both lines at the cooler will be to hot to hold for more than a couple seconds.

And of course change the fluid every 30,000 miles or 15,000 miles if you do a lot of highway driving or towing. Perhpas you could get away with 45,000 miles if you only drive in the city. Would have to get an oil analysis to determine that. That would be interesting to see.


cheers,

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

The radiator tank trans cooler does act as a heater sometimes. The engine water temp is regulated by the fan and thermostat. In very cold weather, the water will reach operating temp because of this, but the trans fluid may not without the aid of the heat transfer in the radiator tank.

BTW, the torque convertor is what makes 99% of the heat in a transmission. It does this by doing it's intended job, slipping. This is how you can sit at a light in drive without stalling. Trans in gear without car moving is where it usually makes most of it's heat, but under certain load conditions, some slippage may occur at speed and also build heat.

If it wasn't for the torque convertor, you wouldn't need a trans cooler. In fact, in some powerglide racing transmissions which have the convertor removed and converted over to a clutch, run without coolers. Lockup convertors use a temp sensor that will lock the convertor up if it's in a high gear and the trans temp exceeds a certain temp. This is done to eliminate convertor slip and the heat it causes.

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85 300CD
83 300TD
78 240D (daughter)

Not a lot of horsepower being produced with the engine idling in gear.

Much more heat produced on the highway where the horsepower really comes into play. The difference between engine speed and transmission speed is typically 200 rpm on level ground. Head up a grade and this increases to over 300 rpm. We're talking a lot of heat...............

But the difference between engine speed and transmission speed with the car in gear and not moving is much more than that. At highway speeds, the more RPMs you're turning, the less slip there is. The less (and closer to the stall speed), the more slip there is. Add a trailer or load the car down or otherwise increase the load (such as climbing a hill) and you'll increase the amount of slippage for any given speed. Having the convertor close to the stall speed is where the most heat is usually generated. If you've brave, then place car in drive, hold brake and rev up against the stall speed and see how fast the trans heats up.

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85 300CD
83 300TD
78 240D (daughter)

.......but with negligible horsepower output..........

The more rpm's you are turning.........the greater the highway speed.........the more horsepower required..........the more slippage there is.

Not neccessarily. If you are operating at close to or less than stall speed, you'll have much more slippage. At higher speed, the extra "load" is in wind resistance, rotating weight, etc. In my example above, little HP is required compared to highway speed to hold the brake while in gear and approach the stall speed, but this will make much more heat than travelling at highway speeds.

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85 300CD
83 300TD
78 240D (daughter)

As I attempted to convey to you, the difference in speeds is only part of the equation. The horsepower lost to heat is dependent on the difference in speeds between the two shafts as well as the actual speed of the input shaft (the engine).

In the case of holding the brake at idle, there is a significant difference between the two shafts (700 rpm), but the input speed is very low (700 rpm). Therefore, the horsepower lost to heat is also relatively low.

On the highway, the difference in speed is about 200 rpm on level ground, however, the horsepower lost to heat is significantly greater because the input speed is now 3000 rpm.

I have not calculated it, but, the horsepower lost to the torque converter at highway speeds is probably greater than the horsepower lost at idle even though the speed differential is greater at idle.

i agree with brian on this.

why would you want to hold the car in gear and rev up the motor? it is an unnatural thing to do.

highway speeds will generate the most heat, and hills or towing will be the max you can do on the highway.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Given that the overflow nipple has already broken off on my 38 year old plastic radiator, and that I am considering replacing it with a modern all metal radiator. And at the same time, considering replacing the old A/C condenser with a Parallel flow condenser, even though I plan to convert back to r12. I am thinking a proper Transmission Fluid Cooler would round out the picture nicely.

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'83 300D (220000 miles and counting)

Years ago on a turbo 350 trans, radaitor cooler rotted out, mixed coolant with ATF, burnt clutch pak. I remembered, a racing magazine, where a guy used his AC cooler for trans cooler. Tranny out lasted many. w140's S600 use external cooler, no damn radiator for hot ATF. W140's and newer model's suffer radiator cooler failure's. So external cooler's will save thousand's

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

MB had an optional trans cooler for W124s and W126 that were used for towing. It mounted where the OM603's engine oil cooler is, and had a thermal switch and electric fan to help when in traffic.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.