Author Topic: Transmission fluid reading  (Read 1142 times)

daantjie

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Transmission fluid reading
« on: 11 November 2019, 05:23 PM »
Hi guys

I had some minor leaks on the trans fluid cooling circuit which I attended to recently, and consequently lost a fair bit of fluid.  Now I am having a helluva time trying to fill the trans to the correct fill level WTF :o

I added about 500ml, then let the motor run and warm up, then it read way high, so I drained some off, too low again, then eventually I got it to read at the full mark with the motor idling, in P and fully warmed up, also running the shifter through the different positions, and then letting it sit again for about a minute before taking readings.  All looked fine last night, right at the full mark.

Now today, with fully cold motor, it reads about 20-25 mm ABOVE the full mark HUH?  In the 3 speed trans manual it says that with fully cold engine it should read about 30mm BELOW the low mark :o

Am I going (more) crazy here, what the heck is going on???

Cheers
« Last Edit: 11 November 2019, 06:57 PM by daantjie »
Daniel
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ptashek

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Re: Transmission fluid reading
« Reply #1 on: 12 November 2019, 12:09 AM »
It is a fiddly job alright. It's not enough for the motor to warm up, the tranny must be up to running temp too and that takes a good few miles of driving. I've never attempted this on a cold engine.

The difference between min and max fill is around 100ml if memory serves.

The way I usually do it is go for a drive, check the level, add 50ml at a time, cycle through all positions for a couple seconds, check again.
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daantjie

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Re: Transmission fluid reading
« Reply #2 on: 12 November 2019, 06:17 AM »
Thanks.
I am still perplexed though, in that in the service manual it seems to lean towards a cold measurement to be the most accurate @ 20 - 30 C ambient.
I would think that the pan will get fuller as the engine cools down due to fluid draining down, so how can you measure it "right" with engine running, knowing that the volume reading on the stick will rise :o?
Daniel
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Squiggle Dog

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Re: Transmission fluid reading
« Reply #3 on: 12 November 2019, 08:28 AM »
In my opinion, the truest measurement will be after a long hour drive with the transmission fluid at maximum temperature, as it seems to expand quite a bit with heat. If the vehicle is only just warmed up, the fluid will likely read low due to the fluid not being very hot. When checking the transmission fluid level cold, looking for the level to be 30mm below the minimum mark may well be accurate as long as the engine is running. What certainly wouldn't be accurate is checking the fluid level without the engine running. I think accuracy depends on either 1. checking the fluid level against 30mm below the minimum mark with the engine running and cold, or 2. checking the fluid level between the minimum and maximum marks after the vehicle has been driven for a long time and allowed to get hot.
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daantjie

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Re: Transmission fluid reading
« Reply #4 on: 12 November 2019, 09:06 AM »
Thanks SDOG, I think I might have erred in trying to check the fluid cold, whilst not having the motor running.  However I still think it is reading way high cold, even with engine off, unless of course a lot of fluid gets put back in the trans as you fire it back up, which may well be the case.  I guess I need to run the motor full hot and take a heat gun to the pan to make sure I am @ 80C to finally put this one to rest.
Daniel
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TJ 450

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Re: Transmission fluid reading
« Reply #5 on: 12 November 2019, 07:13 PM »
Yep, this is very tricky to get right. You're better off erring on the low side then getting that fluid up to temp (80C) and then correcting.

Tim
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Squiggle Dog

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Re: Transmission fluid reading
« Reply #6 on: 12 November 2019, 07:34 PM »
Thanks SDOG, I think I might have erred in trying to check the fluid cold, whilst not having the motor running.  However I still think it is reading way high cold, even with engine off, unless of course a lot of fluid gets put back in the trans as you fire it back up, which may well be the case.  I guess I need to run the motor full hot and take a heat gun to the pan to make sure I am @ 80C to finally put this one to rest.

You're welcome. I believe that when the engine runs, the torque converter sucks up a bunch of fluid from the pan and pushes it through the rest of the transmission, which lowers the level on the dipstick.
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