External Transmission cooler?

[V8 00USH]

Originally Posted by Clockwork

V8 00USH, I have to ask, why did you add in the Mocal brand thermostat? .

Simply because I didn't want to risk overcooling the transmission fluid - after all I went for the largest oil cooler that would fit in the space. As it is the transmission fluid now sits perfectly at the thermostat temperature - if I hadn't fitted that then more than likely it would be sat under that which then wouldn't be at all desirable for the gearbox.

[Clockwork]

So the Mocal thermostat is set to open at what temp?

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[V8 00USH]

Originally Posted by Clockwork

So the Mocal thermostat is set to open at what temp?

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Approx 80deg C

[snik]

I haven't read the entire thing. I'm about to go to sleep. But my 4.8iS threw the ole transmission overheat at me again today for the 1st time since the atf fluid and filter change and new seals.
Granted it was well over 100F today in San Antonio, but I wasn't rowing anything or driving aggressively.

So after a bunch of research and talking to a friend. I think I'm gonna bypass the OEM tranny heat exchanger and run an aftermarket cooler up front.

I will catch up on the rest of the thread tomorrow.


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[bcredliner]

Originally Posted by snik

I haven't read the entire thing. I'm about to go to sleep. But my 4.8iS threw the ole transmission overheat at me again today for the 1st time since the atf fluid and filter change and new seals.
Granted it was well over 100F today in San Antonio, but I wasn't rowing anything or driving aggressively.

So after a bunch of research and talking to a friend. I think I'm gonna bypass the OEM tranny heat exchanger and run an aftermarket cooler up front.

I will catch up on the rest of the thread tomorrow.


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OE system is more than adequate except perhaps in heavy towing in the mountains. I would troubleshoot the problem and determine the cause. Overheating may be a symptom rather than the cause.

[snik]

Originally Posted by bcredliner

OE system is more than adequate except perhaps in heavy towing in the mountains. I would troubleshoot the problem and determine the cause. Overheating may be a symptom rather than the cause.

I disagree it's adequate, but I do think something else is amiss. That said, no errors with INPA since the filter, fluid and seal change.
So whatever it is, it's not giving me a clue.
Everything shifts fine, and smooth. 1-2 downshift coming to a stop is sometimes rough when it's hot as balls out.
So I'm putting on a better cooler.


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[bcredliner]

I don't understand how you can conclude the trans cooling is inadequate when something else is amiss. Might save some time and expense to have transmission diagnosed at a trans shop.

I have over 118,000 Texas miles on a heavily modified 4.6. Trans has Dinan software and I change the fluid and filter about every 40,000 miles with ZF fluid. Never a problem with cooling or anything else. That is anecdotal but poor OE trans cooling hasn't been a common thread here to best of my memory. Just FYI.

[snik]

Originally Posted by bcredliner

I don't understand how you can conclude the trans cooling is inadequate when something else is amiss. Might save some time and expense to have transmission diagnosed at a trans shop.

I have over 118,000 Texas miles on a heavily modified 4.6. Trans has Dinan software and I change the fluid and filter about every 40,000 miles with ZF fluid. Never a problem with cooling or anything else. That is anecdotal but poor OE trans cooling hasn't been a common thread here to best of my memory. Just FYI.

It may not be, but I think the atf is allowed to run too hot. 200F with no towing shouldn't be seen.
ATF doesn't hold up to heat like engine oil does.
Maybe the cooler is adequate, maybe a cooler thermostat is the solution. Either way, the short life of the rubber seals and the solenoids failing. Which both lead to other issues. Do you really think that just happens because of how they're made? No, the transmission runs way too hot and essentially slowly cooks all the rubber and plastic parts which causes other issues.

Think about that. Take the average diesel HD pickup. They run 170-180F ATF driving around and only go up a tad more when towing.
With 180F ATF, can you imagine what the temp is inside the torque converter.

I'm no expert, but I truly believe most of the issues with these X5s would be avoided by running cooler. That's engine and atf thermostats.


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[V8 00USH]

Snik - I am FULLY in agreeance with everything you've said above. Hence doing what I did and hence changing for an 88 degree coolant thermostat too at the same time as doing my chain guides recently.

I'm a firm believer that if the fluids were ran slightly cooler from factory then everything would last significantly longer. Only reason I believe coolant temps were designed to run at the level they are was to meet emission requirements.

Since my changes my coolant now sits at around 95degrees (13degrees cooler than before) and my transmission fluid sits between 75-80degrees and has been considerably happier for the past 25k+ miles

[bcredliner]

I don't recall the following being challenged: https://xoutpost.com/bmw-sav-forums/...s-summary.html. Phil is our resident expert on transmissions, might want to PM him for input.

Transmissions and engines are designed to run most efficiently at a specific operating temperature. The same is true of the life of components.

Lots of my laymen solutions sounded very logical but I have learned over many decades to find verification from the MFG or aftermarket performance suppliers. When there is a design weakness or flaw there are often MFG revision part numbers. When there is a chronic weakness that the MFG has not addressed there are often aftermarket solutions well recognized as a design improvements.

It's true that engine temperature is specified to help meet emission standards. That doesn't mean it shortens the lifecycles of components or that by reducing the temp the life can be extended beyond the design specs.

I'm not saying either of you are wrong, or trying to change your mind. I can see you are convinced you are right. I am saying you have no expert verification for what you are doing. You don't know you are right.

I been where you are many many times over the years especially early on. Usually I was doing what seemed to be logical to save money, in denial. My advice is to close that gap between what you think you know and what you don't know as part of your decision. For what it's worth I've learned it is far better to do the right thing the first time. Lots less pain, suffering and cost over the long run. Good luck