Transmission Fluid Levels

Seymour Legge

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Dear All,
I understand that ATF levels in automatic gearboxes are important and that they should be measured with the engine running and at particular temperatures.
I also understand that accurate temperature readings can be obtained using the Star equipment.
I was wondering if there was "a rule of thumb" means of establishing the correct temperature. For instance, once my engine is well and truly warmed up after many miles and hours of motoring the coolant is stable at 90 C. Can the same be said to apply to the transmission fluid - after, say, 2 hours and 100 miles is it reasonable to assume that it is at around 80 C ?
I should add that I have the correct Tx dipstick marked with 25 C and 80 C bands.
Sorry to ramble
 

DSM10000

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Good afternoon and welcome.

I think that your assumption should be a fairly safe one!

You can buy Infra Red thermometers quite cheaply (although I have no idea how accurate they may be) to check the gearbox temperature from outside :)
 
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Seymour Legge

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C220 Saloon
That had occurred to me but iirc the gearbox sump is contained with a heat shield/fairing; also the car seems pretty low and I am a bit tubby.
I had considered trying to thread a thermocouple down the filler tube, but it seems very long and serpentine. Imagine my red face if it got stuck or broke off inside!
Sorry to ramble.
 
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Seymour Legge

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Dear All,
This is only my third post and it will be patently obvious to readers that the principle reason for signing up was to pick your brains.
With over 93,000 members I am amazed that no-one has driven from Birmingham (or similar) to Brighton (or similar) via the M25 (or similar) and then had occasion to measure or have measured the Tx temperature.
DSM10000 thought that my assumption was reasonable and I still do. I fondly imagine that 25 C represents a cold start and a few minutes to circulate around the system's nooks and crannies and that 80 C is the steady state temperature - but I would love confirmation or comment from someone who has done it with proper temperature measuring instruments.
Sorry to ramble.
 

markjay

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The engine cooling system has a thermostat that regulates the temperature hence why it is steady after warming up.

I don't know if the transmission fluid's temperature is similarly regulated, but if it is not, then there is no reason to assume it will have any sort of steady temperature.
 

Lyserman

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I have just done my C32 transmission level using STAR.
I drove 6 miles from Plymouth back home, parked in the garage, shut down the engine, made a cup of tea, connected the STAR to the car, started the car, selected D and the transmission temp was 83 degrees and stayed roughy there until I had finished.
I had to remove 750ml to get it at the right level and it has improved the shifts.
So I would say a trip of Birmingham to Brighton will get the box at the correct temp.
Tony
 

E55BOF

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You're worrying too much. Get the level correct at 25 degrees C (or thereabouts - ambient in summer will do), drive it for a few miles, then check it. If it was correct at 25 degrees, it will almost certainly be correct when it is hot.

It's just an old car with an old design of transmission, and MB could just as easily have given measurements for 'hot' and 'cold'. It's not rocket science, whatever the purists might like to think. All this nonsense about measuring the temperature to ensure it is spot on at 80 degrees is for the OCD brigade.
 

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