Hot Automatic Transmission

[mdsalemi]

Gents,

Last Thursday night, I decided to "cruise" the Woodward Dream Cruise circuit.  http://www.woodwarddreamcruise.com/

It was in the low 80's, cloudy, but the stop and go, 5-10 MPH traffic had my temp gauge climbing to that notch between the comfortable 180 and the RED line of danger.  I don't like the temp getting to that middle notch so I suffered with the defrost on full which did abate the situation...

ANYWAY, of course the car was running hot, and when I finally got out of the mess on the way home, my auto transmission, which by association was also hot, seemed to be acting peculiar.  Mostly odd shift points--not shifting when supposed to or shifting too early.  Can't exactly put my finger on it, but it was weird.  Once I got some "air time" and the temp came down, the tranny was back to normal. (BTW it's a factory rebuild with less then 5K miles on it)

Anyone experience this before?

Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored

[Benz Dr.]

One thing you can do is take your car out of drive and use a lower gear. This seems to take some of the load off the trans and let the engine idle at a higher speed.

I noticed the same thing on your car while I was in line waiting to get into the RM 25th aniversary show last year. I put it in a lower gear and then in park when I wasn't moving. Once the temp creeps up it usually stays up until you drive away and get cool air flowing across the oil pan.
 I think this supports my findings that there isn't enough oil cooling or capacity as well as the fact that the trans ads extra heat to the cooling system that has to be handled by an overheating engine.

A lighter coolant mixture along with water wetter might help out a bit.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org

[TheEngineer]

Hi Mike: I have noticed that the shift quality of my transmission changes with temperature: When the transmission is cold, the 2 - 3 upshift is so smooth, it can only be distinguished by observing the tachometer. It's like that every time I leave home. After the car becomes good and warm, the upshift sometimes is not so smooth anymore. It appears that the transmission is sensitive to changes in the viscosity of the oil. I'm using Dexron 3 but one fellow told me at the last MB get-together, that the transmission shifts better using Ford type A. He said, it was designed for that. I have not tried it. As to your overheating problem: I noticed that the standard radiator has two rows of coolant tubes. Mine has three. I have A/C and an air-conditioning radiator in front of my radiator. I have never had an overheating problem. My fan has a viscous clutch. I'm using Duracool 12 refrigerant and the temperature at the outlet is about 40°F

'69 280SL,Signal Red,007537,tired engineer, West-Seattle, WA