News:

www.W116.org - The #1 resource for our W116! Established 2004

Main Menu

Transmission fluid level

Started by raueda1, 06 August 2020, 10:35 AM

raueda1

The good news is that I've been putting a lot of miles on my resurrected car.  Several thousand in fact since putting it back together - lots of long, high speed travel in the great American West.  What amazing cruisers these things are! 

The bad news is that I've got a small transmission drip.  It's not much more than an occassional small spot after parking, but still there.  What it boils down to is having to top off the tranny after 1500 miles or so.  In doing this I discovered that the marks on the dipstick correspond to a surprisingly small amount of fluid, roughly 1 cup (~250ml).  That is, if you're down to the lower line it will just take a cup of ATF to bring it back to the top.  Maybe even less.  Several times I way overfilled and had to suck ATF out.  It's hard to break the lifelong habit of just dumping in half a bottle of ATF.  Accurately hitting the top line on the stick is pretty hard, it's very easy to overfill a little bit.

So here's the question:  how sensitive is the tranny to a slight overfill?  Or running very slightly low for that matter?  For some things "pretty close" isn't close enough and I don't want to damage anything.  Regardless, I'm going to monitor carefully going forward.  Another 2000 miles of road trippin' is on tap for the next month or so.   :)  Thanks and cheers,

-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

ptashek

Quote from: raueda1 on 06 August 2020, 10:35 AM
So here's the question:  how sensitive is the tranny to a slight overfill?  Or running very slightly low for that matter?  For some things "pretty close" isn't close enough and I don't want to damage anything.  Regardless, I'm going to monitor carefully going forward.  Another 2000 miles of road trippin' is on tap for the next month or so.   :)  Thanks and cheers,

It's actually closer to 100ml if memory serves. Tiny, tiny amount anyway.
My 450SE also sweats ATF around the drain plug, even though everything there was renewed. But it's a few drops over the course of a year, barely enough to leave a spot on the ground. I've no idea why, to be honest.

Now to your question. As I understand it, the 722.x trannies are more sensitive to overfilling above max, than running somewhere between min and max. The manual says they should  sit at the max mark at 80*C ATF temperature for optimal operation. Apparently the reason why over- is worse than underfilling is that the ATF is getting beaten into a froth, and all that can cause issue in the pump, the valve body and down the line. But that's what I've read, not experienced, so who knows if that makes any sense. Someone here is bound to know for certain :)
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE

revilla

I echo the same experience of small leak and touchy to hit the max mark on the spot. That happens to me also when changing the oil and filter. The technique that I found the most optimal is to overfill a little, run a few miles and then measure. Then undo the oil cooler hose at the radiator (lowest circuit point and easy accessible) to let some drops out, until the max mark is accomplished.  This is certainly easier than sucking oil from the filler tube.

I read in several places too that overfilling is no good.  But I don't know of the technical reasons why.  As you, I'm interested too in a more educated guess.  Hopefully somebody with the knowledge can shime in.
Thanks in advance

raueda1

Great info, just what I was looking for.  Thanks much!  Seems like a strange design choice to make the fill range so small, kind of invites mistakes.  Anyway, I shall pay very, very close attention going forward.  On the bright side, the car seems to lose no oil at all.  After rebuild I was nervous about  blowby, bad valve guides/seals, rings not seating right etc etc.  No problems there (knock wood).  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

Haha yes this is a topic which has also confounded me over the years...If you check the trans manual, it states that the most accurate way to measure is actually with engine cold and off, @ ambient of (I think) 20C.  Then from memory it says that the reading should be 30mm (again, from memory) BELOW the low mark on the stick.  This is where it gets squirrely to me, as with engine cold my fluid actually reads way high on the stick, and then once you fire it up and the fluid starts moving you can start seeing it show up on the bottom of the stick, creeping up as it warms up.

I have stuck to the hot engine, running in Park approach, I really do not see how the cold engine reading would be "best" as per the manual, but then again what do I know ::)
Daniel
1977 450 SEL 6.9 - Astralsilber