TheClairvoyant

My car is an 86.5 automatic. There is a small cooler just behind the grill in front of the AC condenser and radiator.

Is this an external transmission cooler?

One hose runs from it to the passenger side radiator tank. I can't see exactly where the other hose runs until I get under the car.

I know later cars had external oil coolers, but I couldn't find anything about external trans coolers coming from the factory, just the cooler tank built into the radiator. I believe the part is original to the car.

ammonman

Correct. External trans cooler.

Mike

brutus

used in series with the in radiator heat exchanger so your car has both !

TheClairvoyant

Thanks.

Is it common to have the external trans cooler? I never read about it previously. I searched and couldn't find anything on the forum.

Just curious.

Podguy

The 85-86 was the first one I think. On the later cars the trans cooler is bigger.

I do not think 83-84 had one. - only the radiator. Not sure it does much to make the trans last much longer. Take a careful look at the small short hose on the radiator - this one likes to leak.

brutus

As the horsepower increased the waste heat in the trans increased so they added cooling to help control it. S-4 has a larger air/oil cooler and a thermal switch on the trans which turns on the cooling fans as I recall.

Tom in Austin

On GTS, there's a second AT cooler atop (or maybe even integrated with?) the A/C condensor ... fluid goes through the radiator-tank AT cooler first, then around the radiator and into the second cooler.

I've wondered why they choose the dual-cooler approach, seems they would have just made one sufficiently large heat exchanger. Is there some technical advantage to a dual cooler design?

brutus

The liquid to liquid heat exchangers are far more efficient and therefore much smaller but are working in 190 degree coolant the hot side of the radiator , liquid to air needs to be much larger to shed heat but is in much cooler air.
There is really not much room to put a large enough air/oil cooler in front of the radiator without blocking and heating the A/C condensor.
Greg Brown has started using both the radiator engine oil heat exchanger and the external engine oil cooler ( late cars) to get better control for the engine oil temperature. He has made special hose just for this modification.

Maybach_Man

84 euro's have them

brutus

They too were churning 300 plus HP into that trans fluid ! maybe why the 83 Euro stayed with the three speed auto ?? Which according to one Mercedes trans specialist is the stronger automatic.

PorKen

The extra radiator coincides with >250 TQ at the tires?


'84 euros are rated at 295 TQ vs. 263 of the earlier S engines (via bigger cams and LH/EZ).

The '85 32V is rated at 302 TQ.


Looking at it another way, the radiator corresponds with Digital Engine Management.

PorKen

FYI: the plug on the end of the cooler is for a temp switch, part of the M208 factory towing option.

The switch grounds the orphan wire near the jump post, pictured, turning on the A/C fan.

(All S4-up autos have a similar switch in one of the cooling lines at the transmission.)

Maybach_Man

Wow always wanted to know what that connector was for

PorKen

Note that that wire is in parallel with the radiator and A/C temp switches, so could be used to ground (earth) an aftermarket fan relay.

(Inside the square plastic housing is a male spade terminal, just like the A/C compressor connector.)