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  #1  
Old 08-30-2004, 05:04 PM
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Location: Oakland, Calif.
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ATF: Is "too full" always too full?

Hi, everyone,

Sorry to start another transmission fluid level thread, but I haven't been able to find a definitive answer to this, and it's bedeviling me.

Most advice here and in the repair manuals seems to say that the transmission fluid should be at or below the maximum mark on the dipstick with the transmission at a “normal operating temperature” of 80°C. Many of the posts here suggest that this can be attained by driving the car for 20 minutes or so on the freeway. But here are my questions:
  1. How can I be sure the transmission is really at 80°C when I check it (not just "pretty hot")?
  2. Does this specification allow for the transmission fluid to go above the max mark if the transmission is hotter than 80°C (e.g., could it get up to 100°C under hard or hot driving conditions? Even if the engine isn't that hot?)
  3. If so, what's the highest "safe" level for the fluid on the dipstick when the transmission is "really hot"?

Most of the time I’ve had the car, the transmission fluid reads about halfway between min and max on the dipstick after easy driving in the city for 10-20 minutes. With this amount of fluid, the transmission shifts reliably, but often with a solid “kick” as it shifts up around 20-25 mph. However, after heavier freeway driving (e.g., 30 minutes at 70-75 mph, on a warm day), the fluid reads about 1/4"-3/8” above the maximum mark. During a long, hot road trip with a bad radiator cap a couple of weeks ago, I removed 8-10 oz of transmission fluid to get it down closer to the max mark, but then as the day got hotter and the hills got steeper (engine temperature up to about 100°C), the level went back up to about 1/4" above full. I left it at this level, but then, once I was home and everything cooled down, the transmission seemed to shift later and less decisively. At that point, the fluid was about 1/8” above the tip of the dipstick when cold (maybe about 3.3 cm below the minimum mark). Even driving for 20 minutes uphill (on a cold day), it didn’t come back up to the maximum, so I added about 6 oz. of ATF, which I think brings me back to about where I started (and brings the performance back to where it started). Now, if I drive 30 minutes on the freeway at 70-75 mph, the fluid is up to about full+1/4”, but otherwise, it is usually between max and min.

So, the question is, is the fluid at the right level now, or should I take some out, so it _never_ goes above “max”? Also, if it’s too high now, is it likely that any damage has been done to the transmission by driving hard with 6-10 oz. of extra ATF, and possibly staying at that level for years (I don’t know how full the previous owner usually kept it)?

Thanks for your help!

Matthias

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  #2  
Old 08-30-2004, 05:27 PM
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Cool

On that car with a 722.118 transmission you should start the fluid level 20-25mm BELOW the lowest mark when the fluid is cold! Never should the fluid level go above the highest mark.
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  #3  
Old 08-30-2004, 05:39 PM
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Your post seems to be asking excellent questions, basically, what constitutes "normal" with respect to operating temperature when you are not able to measure that blasted fluid to see whether it is at 80 degrees C, and then have you filled it to the correct level for whatever temperature it was at when you did the work?

I venture there may be no simple answer, except to suggest that your first advice to run it for about 20 minutes was the best advice. You see, the transmission is cooled by the radiator and once the car runs up to normal operating temperature and stabilizes there, the transmission oil will likewise have attained approximately the same normal temperature as the radiator, roughly 180 degrees F these days and which happens to be, coincidently, very close to 80 degrees C. Therefore, setting the fluid level to the proper mark after warming up as advised should be fine.

The transmission is designed to accomodate fluctuations in level due to temperature changes, but over-filling can be bad if the rotating internals foam the oil, the pump will pick up air bubbles rather than oil. Filling to the upper mark when cold will cause the transmission to be too full when hot; filling it to the lower mark when hot equates to under-filling which could lead to a dry pump suction if driving conditions stack up against you. This is also bad news. So, set the oil level as previously advised, look for tell-tale red spots beneath the car and change the oil often to keep the transmission healthy.

For what it's worth...

230/8
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  #4  
Old 09-02-2004, 01:52 AM
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ATF overfill

I just changed the ATF on my 89 300TE tonight, added 4 qts like the factory manual said, started the engine, ran in through the gears as prescribed, and checked the fluid level. It reads overfull by 10-15mm! What's up? The expected fluid change was 6.7 qts according to the manual. Where did I go wrong?
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  #5  
Old 09-02-2004, 09:17 AM
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Did you drain the torque converter??
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  #6  
Old 09-02-2004, 04:22 PM
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Nope, just the pan. I got more than a gallon out when I drained it.
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  #7  
Old 09-02-2004, 06:42 PM
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Since you left 1/2 of the fluid capacity in the converter you needed only 1/2 of the total quanity.
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  #8  
Old 09-02-2004, 11:36 PM
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Transmission fluid expands when hot, quite a bit actually, so it will read high when the tranny is quite warm, as in climbing hills, etc.

Check it after driving enough to get it up to operating temp, and make sure it stays below the top mark in those conditions, and you will be fine.

Towing a heavy trailer in the mountains will require an additional cooler to keep it from "overfilling" due to heat and associated tranny failure. I've seen this several times, it's not fun.

Peter
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  #9  
Old 09-03-2004, 07:14 PM
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psfred wrote:
Quote:
Transmission fluid expands when hot, quite a bit actually, so it will read high when the tranny is quite warm, as in climbing hills, etc.

Check it after driving enough to get it up to operating temp, and make sure it stays below the top mark in those conditions, and you will be fine.
Thanks for the advice. Just to double-check, does "those conditions" in your second sentence refer to normal operating temperature (e.g., around town, on flat freeway, engine temperature a little above 80°C), or to the hard-driving conditions, like crossing mountain passes (no trailer, but engine temperature getting up to 90-100°C)? Should I make sure the transmission fluid level is always below full (which might require removing some on long, hot, hilly drives), or just that it's always below full when the transmission is at normal operating temperature? Sorry if I'm being dense, I just wanted to be sure.

At this point, I'm assuming that the right thing to do is to get the fluid level to "full" when I've been driving around town or on the freeway for 20 minutes or so, with the engine up to about 80°C (which I think will also correspond to about 30 mm below the minimum with the transmission at 20-30°C). Then, if it goes a little higher when I'm out climbing over the mountains, I assume that's OK too. This is contrary to what M.B. Doc said on 8/30, but seems to match what 230/8 suggested, and what I've been able to glean from the service manual. For what it's worth, even with the range of temperatures and levels the transmission fluid has been at (up to about 9 mm above max at the hottest/fullest, or down to about 35mm below the minimum at coolest/least filled), I've never noticed any bubbles or burnt smell on the dipstick. The worst I've had is hesitant shifting (and maybe a hint of flaring) at low fluid levels.
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  #10  
Old 09-03-2004, 09:23 PM
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Check at normal operating temperature after driving long enough to get the tranny fully up to temp (about 20 min).

There is space in the transmission for the fluid to expand in normal service. If you decide to tow a boat or large trailer, etc, get an accessory transmission cooler, else it will overheat.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #11  
Old 09-09-2004, 12:55 AM
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89 300TE trans slipping

I should have posted this reply here, instead of as a new thread:

I have a 89 300TE with 155k miles, trans replaced at 100k with rebuilt (not by dealer). I bought the vehicle 18 months ago, and have had no troubles (with the tranny anyway) until recently. Last week I started noticing a slight delay as the car shifted from 3-4. Now it's more noticeable, although not always consistent, and I'm begining to feel it in 2-3. I changed the fluid two days ago, everything appeared normal- no discoloration or material in the pan. My next step is to take it to a transmission expert, since I'm an hour away from the nearest MB dealer. Any thoughts or recommendations would be much appreciated.

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