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Discussion Starter · #1 ·
So my transmission has been overheating for a few months now but for a while I was thinking I just needed a rebuild and was putting it off, until recently when I realized that the harsh 3-2 and 2-1 downshifts were happening after an extended drive. I used INPA to check the analogue data in the transmission and noticed that whilst driving the transmission would get up to 245 degrees F and higher! This directly coincided with the poor shift performance as well.

Today I replaced the Trans lines that run from the trans heat exchanger along with the two little coolant hoses that come off of the heat exchanger as well. I also replaced the trans filter thinking that the old chinese one might have been a cause of some of my problems. It drives slightly better (probably the new fluid because old fluid was slightly burnt) but still overheating and harsh 2-1 shifts (Less harsh than before)

What could be the cause? I have ordered a replacement transmission thermostat, the black thing on top of the oil cooler which bmw calls a voltage regulator?? The only other thing I could possibly thing of is that I seem to have a leak in the plastic part of my radiator close to where the coolant line that feeds into the trans oil cooler is. Could the leaky radiator somehow be making my transmission overheat?

To me the only logical cause could be the tstat not functioning, I cleaned the absolute hell out of the oil cooler itself and the flow seems to be okay inside of it, could the cooler itself be causing issues?
 

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2001 BMW E39 540i Automatic Sedan, 200 k miles
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First, which car model, year, mileage and transmission are we dealing with ?

Second, test and find any leaks in the cooling system (hoses, radiator, tank,..etc..), and fix them.

Third, stop throwing parts (are these after-market parts ?) at a problem, until you find the exact source or cause. You may be only making things worse.

Fourth, why do you think 245 F is too high temp for the transmission ? It may well be, but..
 

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So if you have the GM 5Hp24 automatic transmission it could be the pressure regulator in the valve body. The harsh down shifts are a common symptom. There is an aftermarket solution or you could send it out for a rebuild. As Chedley said I'm not sure why you are throwing dollars at it. Maybe the trans fluid and filter R&R was something to consider but it didn't fix it so do a search in the forum.
 

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245F is hot, my 528i Stepronic auto transmission runs at 76C or 168.8 on highway, it may go up a few degrees at times but I think I have only seen 80C a few times. It鈥檚 a 6 cylinder though so a V-8 probably runs hotter, anything over 220F is cooking the trans fluid.
 

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2001 BMW E39 540i Automatic Sedan, 200 k miles
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Well, then maybe the OP should start with replacing the transmission fluid and filter, and see if the over-heating persist.. It is critical that you use the right fluid (ZF or Pentosin-ATF-1 synthetic). Buy it from the dealershipl if in doubt.

Note; The 5HP24 is a pretty sturdy transmission. I have it on my car, and at 203,000 miles, never a problem. Although I make sure I replace the fluid and/or filter every couple years.
 

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Discussion Starter · #6 · (Edited)
First, which car model, year, mileage and transmission are we dealing with ?

Second, test and find any leaks in the cooling system (hoses, radiator, tank,..etc..), and fix them.

Third, stop throwing parts (are these after-market parts ?) at a problem, until you find the exact source or cause. You may be only making things worse.

Fourth, why do you think 245 F is too high temp for the transmission ? It may well be, but..
2003 540i, ZF 5HP24 181K miles. Yeah I have a leaky radiator and looking to replace it.

As for the parts, I replaced the transmission fluid lines because I was going to take them off and check if there was a blockage or something but the old lines were in pretty bad shape and the quick connectors were broken, I decided to go ahead and replace the lines, probably a foolish purchase but I feel better knowing that I won't be leaking tranny fluid any time soon. I ordered a tstat because the old one had a bit of a leak where the two parts of it come together, I used silicone gasket maker on it which is holding for now but I was able to get a new tstat for somewhat cheap so I went for it, but yes I know, sort of a dumb dumb for throwing parts at it but what can I say, I'm a sucker for seeing shiny new parts that don't leak on my nearly 200k miles baby.

As for the filter, I had replaced the filter with a very very cheap china filter 20k miles ago and just to stay on the safe side I decided to right my wrong and go with a ZF filter.
 

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Discussion Starter · #7 ·
So if you have the GM 5Hp24 automatic transmission it could be the pressure regulator in the valve body. The harsh down shifts are a common symptom. There is an aftermarket solution or you could send it out for a rebuild. As Chedley said I'm not sure why you are throwing dollars at it. Maybe the trans fluid and filter R&R was something to consider but it didn't fix it so do a search in the forum.
Thanks I think it's either down to the pressure regulator or the tstat at this point but I will continue to do research. If it is the pressure regulator, it looks like replacement parts are both easy to find and relatively inexpensive. Would you happen to know if it's a job that requires anything crazy to complete? I'd like to attempt it myself if this does end up being the problem.

Also, I ordered the replacement t stat because the old one was leaking a bit of coolant, I put some gasket maker on it but decided I would pick up a new one just to make sure everything is airtight.
 

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Discussion Starter · #8 ·
So if you have the GM 5Hp24 automatic transmission it could be the pressure regulator in the valve body. The harsh down shifts are a common symptom. There is an aftermarket solution or you could send it out for a rebuild. As Chedley said I'm not sure why you are throwing dollars at it. Maybe the trans fluid and filter R&R was something to consider but it didn't fix it so do a search in the forum.
One other thing, Wouldn't I have transmission error codes in INPA if it was the pressure regulator? I have read them and there are no errors from the transmission.
 

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2001 BMW E39 540i Automatic Sedan, 200 k miles
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Correct...
Do a regular traansmission serrvice: replace the filter, the pan gasket and the transmission fluid. Use the right fluid (ZF filter and fluid).
 

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Discussion Starter · #10 ·
UPDATE: I swapped out my old pressure regulator valve for the upgraded transgo unit, I also replaced the leaking trans tstat with a new one. The good news is I no longer have a coolant leak from the thermostat, the bad news is my transmission is still acting up.

I made a video that shows what is going on in, basically after the car is warmed up and when slowing down below 15-20 MPH: The car will buck when going from 3 to 2 sometimes and will buck really hard when going from 2 to 1. sometimes if I come to a stop very gently the bucking will either be not so bad or not happen at all. Sometimes when I'm going under 5 MPH and in 1st gear the car will buck and it is as if the brakes are on? Like the transmission is holding the car still, if I shift into Sport mode, semi auto mode, or drive while this is happening then it instantly releases and I start rolling forward, then shortly after it will come to an abrupt stop almost like there is a brake in my transmission.

Here is the video, I believe it gives a pretty good description of what is going on.
 
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