ATF Dip stick - correct measurement method

[television]

These dipsticks are quite a clever design by MB.

For the gearbox, the important oil level is the distance between the oil pickup and the oil's surface. The oil pickup is mounted to the body of the gearbox, not to the sump. The sump is a loose tolerance pressed part fitted with a flexible seal - it's not a good datum for a measurement.


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The difference in tolerance is going to be no more than 1mm

The level is around 2 points with a 10mm spacing.

Since a thermometer is not used to check the temp a difference of 1 mm from a height of fluid at 5,6 cm is going to make no difference at all

It is a sump and nothing else

 

[Number_Cruncher]

>>It is a sump and nothing else

Yes.

I think you might be surprised on the issue of tolerances though.

What I was describing is how the MB dipstick actually works. It has been designed using the same German logic that gives us 0.01mm wheel bearing clearances!, and this engineering logic applied all over is what makes the cars as good as they are.

I know these points make no sense at all to pragmatic British tinkerers, but, look what's happened to our car industry!

 

[television]

>>It is a sump and nothing else

Yes.

I think you might be surprised on the issue of tolerances though.

What I was describing is how the MB dipstick actually works. It has been designed using the same German logic that gives us 0.01mm wheel bearing clearances!, and this engineering logic applied all over is what makes the cars as good as they are.

I know these points make no sense at all to pragmatic British tinkerers, but, look what's happened to our car industry!

I do appreciate them,,,but not on a sump as no two people will read the dip stick alike. it is only a storage device.
Yes the tolerances have come down now to very fine levels

 

[Number_Cruncher]

>>as no two people will read the dip stick alike.

There you go, being all pragmatic again!

Actually, I think getting the level just right on an automatic gearbox sump must be quite a fine balance to strike.

If you imagine designing the thing, you probably have a constraint not to go any lower than the engine's sump for ground clearance reasons. The gearbox centreline is forced to align with the crank at the bellhousing end, and if anything, the whole assembly will be mounted low down at the rear. This forces you to have a wide, shallow sump.

Once you have a wide shallow sump, you then have the situation where a small increment on a dipstick actually corresponds to quite a volume of oil. You need to guarantee that the pickup will never be trying to slurp in air instead of oil, but you also need to be sure that the oil level isn't so high that the gears churn in it making froth - you need to be sure that these conditions will be satisfied over a range of temperatures, and while the vehicle is accelerating, braking, cornering, climbing and descending hills.

The engine can have a deeper sump, and can sidestep these issues - I think engine sump / dipstick design is easy in comparison.

 

[television]

I almost mentioned the effect of the fluid being picked up, and was trying to visualize the bottom,,I wondering how much splash might take place from the return form the torque converter, but that goes through the cooler so nothing in the way of splash from that,,but one has to allow for high speed cornering and braking,, it is a fine line,all of it

 

[S.Speed]

MB being "clever" with the design of their dipstick is all well and good, but that doesnt answer the fact that MB do NOT make the auto gearboxes!!
Auto gearboxes on other prestige cars (Just as "clever" as MB) seem to manage very well with dipsticks.
To cut through all this we need to know for definate how the level is measured because there is about a 40mm variation between pushing the dipstick to the sump floor or allowing it to stop at the first detent position.
Or to put it another way...All those of us who use the sump floor method have our fluid level 40mm too low (If you measured from the sump floor)..
Come on SAM - UNIT give us a definitive answer please..

 

[Silver_Star]

I can see what you are all saying as the MB stick has a stop and measures down from a constant point on the gearbox case and the home made job measures from bottom of sump upwards. Granted there may be a 1-2mm difference in readings between using a home made vs workshop tool measuring the oil level in the same gearbox. However are we not forgetting though that on the MB dipstick the level for 80degrees there is a good 9mm of tolerance from the min to max of the 80 degrees mark, therefore I really fail to see what it matters if you use the home made job as long as it falls into the tollerance of the 80 degrees marks on the MB stick it will be fine IMO.

Another way to do it would be to take your car to the garage or somewhere with the workshop tool get them to dip it and set the level bang on the middle of the 80 degree mark then put your home made job in and mark the level from the actual oil in there so your home made job will be calibrated against the proper tool, however this is all hassle. A measurement of 56mm up the wire will be fine for the 722.6 box using curtain wire.

 

[television]

MB being "clever" with the design of their dipstick is all well and good, but that doesnt answer the fact that MB do NOT make the auto gearboxes!!
Auto gearboxes on other prestige cars (Just as "clever" as MB) seem to manage very well with dipsticks.
To cut through all this we need to know for definate how the level is measured because there is about a 40mm variation between pushing the dipstick to the sump floor or allowing it to stop at the first detent position.
Or to put it another way...All those of us who use the sump floor method have our fluid level 40mm too low (If you measured from the sump floor)..
Come on SAM - UNIT give us a definitive answer please..

Simon,,MB make their own boxes.

The official MB dip sticks do have a stop as in the picture.
The home made stick does not have a stop and goes approx 1mm further in. The figure of 5.6cm on measuring this way falls within the 80c band on the official stick.
The level is not critical it is a sump, and should be at that approx mark.
There is about 40cm difference between the new fill level (25c) and the hot 80c fill.

A big mistake is made when re filling by many, first on a box that holds 7.5 liters, only 5.5 liters should be put in, then the engine started up. The transmission should then be allowed to warm up to 80c and while doing this the shift should be moved constantly through the gate from P to the lowest gear. Further fluid can then be added.

The difference between the 25c marks and the 80c is 3cm, and the failure to get the box to the correct level temperature is the biggest reason for any over fill. When done on STAR this knows the temperature of the fluid, and an owner doing this would be better off part filling and going for a drive and then re checking and adjusting.

I can see that I will have to do a proper DIY for doing this.

 

[Number_Cruncher]

Malcolm - thanks for posting the piccie, it's very helpful.

As the piccie shows, it's the measurement from A to B, and from A to C that's important, and the MB dipstick design keeps the measurement datum and the item being measured very close together - it's really good measurement practice.

The improved accuracy of the MB dipstick method allows this widening to the ~9mm wide tolerance band, because all of the other sources of innacuracy I mentioned above have been removed by their method.

Once you deviate from the MB method, the 9mm wide tolerance is no longer applicable, you need to work to closer tolerance on your homemade dipsticks.

>>have our fluid level 40mm too low

No, your oil level will not be anywhere near so far wrong (unless your curtain wire bent against the floor of the sump?)

In terms of "cutting through this", have a read of how oil level is managed on the 722.9 gearbox, and you'll find it's an issue MB take very seriously, and as MB have been making some truly excellent automatic gearboxes for many years, they really are the experts.

>>A measurement of 56mm up the wire will be fine for the 722.6 box using curtain wire.

I'm sure you're right, but, what's the tolerance on temperature, and what's the tolerance on oil level? is 54mm OK?

 

[television]

Funny that you should mention the 722.9 I also read much this morning on how the correct levels are obtained,and the mods to the overflow pipe and sump

 

[television]

Just another point on a home made stick,, one could cut the plastic on curtain wire and wrap a wire around the cut,,I have never suggested this as the filler pipe is always cranked
and any round stop could jam in the tube, where as a flat one will not. I am still working on this

 

[panason1c]

Just another point on a home made stick,, one could cut the plastic on curtain wire and wrap a wire around the cut,,I have never suggested this as the filler pipe is always cranked
and any round stop could jam in the tube, where as a flat one will not. I am still working on this

Dodgy territory!..........could be a risk of things coming adrift and falling into the box..........

Wouldnt spending £20 on a genuine MB dipstick be a tad easier and give peace of mind?............

 

[television]

Dodgy territory!..........could be a risk of things coming adrift and falling into the box..........

Wouldnt spending £20 on a genuine MB dipstick be a tad easier and give peace of mind?............

That is the reason I have never put it up

They cost £36 over here,,OK for someone who will be doing their own fluid changes,,so yes to that.

For those who want to check the level as they have a fault,,then the home made ones are fine for this possible one off check that they may ever make

 

[Jonski]

Television, thanks, I'm in this situation you describe... and not wanting to shell out £36 for a one off check, plus I live in France so maybe even more pricey. Just to be clear I've got it right:

- I get a net curtain wire, or stiffish single core copper electric cable about 4ft long.
- I break off the 'sealed for life' cap on the dipstick tube with a screwdriver or pliers or something.
- I push my home-made dipstick into the tube twisting as to pass the 'stop'
- When I hit the bottom of the sump I look for about 56mm of fluid at 80C temp.

Is that right please? How much less that 56mm before I should start worrying?
If the engine temp is only 60-70 degrees does this make much difference?

 

[Silver_Star]

I would go with the net curtain wire, after a good run with the trans oil up to temp (80 degrees) You will need to do a good 10miles to get it warmed up, I went down the motorway a couple of junctions in 4th gear.

The sealed for life cap will snap off then push the bottom half through the cap with a small screw driver or similar then the cap to the tube can be removed.

After you have marked the curtain wire with a marker 5.6CM up from the bottom with the engine running and the box in 'P' push the curtain wire right down to the bottom twisting it till it bottoms out, remove the wire and read your level.

There is a picture on the site somewhere with a tape measure against the worsktop tool so you can see for yourself. If you can't find it I can go and measure mine.

 

[television]

Silver star has spelled it all out,and it works well and certainly near enough

 

[Jonski]

Thanks for the replies. I have done my first measurement, and I measured slightly under 56cm from the top of the dipstick tube down to (what I think is...) the bottom of the gearbox. I can push it further, but I believe that I am then pushing it horizontally along the bottom of the sump. I found approximately 8.5cm of fluid in the cold gearbox without the engine running. I wonder if anyone can confirm that 56cm is the expected length of dipstick from the top of the tube to the bottom of the gearbox, so I can be sure that I have indeed found the real bottom of the gearbox, before I start measuring on a hot & running engine. (Note: the black factory seal was still present when I started)

 

[television]

5.6 cm is the correct level with the gearbox at 80c the cold measurement will be much lower

 

[rich.g.williams]

yes I had that problem, the curtain wire is a bit of a tight fit as it goes through the top of the transmission and it then touches the bottom and buckles up if you keep pushing

if you are not sure try using a thinner more rigid (1mm diam copper) wire to gauge the bottom of the sump then you can compare with, and use the curtain wire knowing exactly where the sump bottom is

 

[Jonski]

Thanks. I've switched to some stiff electrical cable for the makeshift dipstick. It comes to a firm stop at 68cm down from the top of the tube. (so my earlier measurement was wrong). However, no sign of any fluid even at 60 degrees C with engine running. We're snowed in here , but I will try again when I can give the car a run to get it up to 80 degrees. If anyone who has already done this successfully can confirm if 68.5cm is the correct length of dipstick from tube-top to sump-bottom on the W210, it would help take away any remaining doubts as to whether I've genuinely reached the bottom of the sump with my makeshift dipstick? Then I can start looking for the required 5.6 cm of fluid with confidence.