Tranny cooling thermostat

[TiesTorN]

as you know, 99+ 540i's tranny uses water to oil cooling and that's ok. what is not ok is the operating temperature. a constant 100-105c is too high. ZF states that these trannies should be operating between 80-100c and not exceeding 100c but dunno why bmw designed it this way. I can clearly feel that the ride quality suffers after exceeding 100c.

anyway, in a topic I've seen JimLev decreasing the spring tension of an engine tstat by heating it thus lowering the opening temperature. I'm wondering if the same thing can be applied to tranny tstat? I'm seriously thinking of trying it instead of installing an aftermarket cooler. That way I won't need to add extra components to the system and just use the existing cooling system.

my target is 80-85c operating temp for the tranny.

ps: my main radiator is good enough to compensate the extra heat. it's a hot climate version radiator. and my engine tstat is an 88c one.

[TiesTorN]

lol nobody has any idea... again.

[DennisG01]

lol nobody has any idea... again.

Not even 24 hours and you're condemning the entire forum? C'mon - you know the deal... you ask questions on your time and people answer on theirs. You won't win friends with comments like that.

But... back on point... is this the original tranny?

[TiesTorN]

Not even 24 hours and you're condemning the entire forum? C'mon - you know the deal... you ask questions on your time and people answer on theirs. You won't win friends with comments like that.

But... back on point... is this the original tranny?

nope... it's almost 48 hours. topic dropped into 2nd page.

anyway,

what do you mean by original? if you're asking if it's ever been rebuilt then yes, it's been rebuilt twice and cooling system completely overhauled. there is absolutely no problem with it. I'm just trying to improve it.

[JimLev]

Heating the t-stat spring was just a test that ended up not being a viable solution.
You can get the 85 deg t-stat or make a PWM circuit to power the t-stat heater like I did, then you can set the engine temp to what you want.
Or...
Put an external tranny fluid cooler in series with the tranny line.

[jclausen]

Or you could just gut the unit and have it run open, but I would not know if that is a good idea

[DennisG01]

nope... it's almost 48 hours. topic dropped into 2nd page.

anyway,

what do you mean by original? if you're asking if it's ever been rebuilt then yes, it's been rebuilt twice and cooling system completely overhauled. there is absolutely no problem with it. I'm just trying to improve it.

Still, it's "nicer" to say something in a friendlier way, that's all. No big deal.

Yes, was wondering if it was rebuilt/replaced. Reason for that was that if it was original, I was simply going to suggest leaving it as is since it's made it this far. Otherwise, I was going to ask about a lower temp t-stat - but it looks like Jim is already on top of that and he knows more about this stuff than I do.

[TiesTorN]

Heating the t-stat spring was just a test that ended up not being a viable solution.
You can get the 85 deg t-stat or make a PWM circuit to power the t-stat heater like I did, then you can set the engine temp to what you want.
Or...
Put an external tranny fluid cooler in series with the tranny line.

doesn't matter how much you decrease the operating temperature, tranny temp won't change cuz its tstat opening is rated somewhere around 96c. I just wanna lower that somehow.

why didn't it end up viable? me and my friends were seriously thinking of doing it

[Kenny1958]

i removed my tranny stat and put a behind the rad cooler line from another beemer.. I think jcaino has also done it.

[TiesTorN]

yes, apparently he did it and he also wrote about it here while insulting me for wanting an answer lol... jimlev must have deleted those comments. it's curious why he still didn't answer my question tho.

anyway,

as I told him, that solution is not enough. it will keep the tranny around 95c. I need around 85c. tranny feels MUCH better at those temps.

[RosieE39]

Mahle transmission thermostat is 86°C.
https://catalog.mahle-aftermarket.co...76094726936055

[TiesTorN]

Mahle transmission thermostat is 86°C.
https://catalog.mahle-aftermarket.co...76094726936055

I've seen this before and I thought that it's just what the genuine part was rated at. am I wrong? is 86c really lower than what the factory one is? cuz I couldn't find any info about the factory one.

still too much though, opening temp should be around 75c.

[RosieE39]

I've seen this before and I thought that it's just what the genuine part was rated at. am I wrong? is 86c really lower than what the factory one is? cuz I couldn't find any info about the factory one.

still too much though, opening temp should be around 75c.

doesn't matter how much you decrease the operating temperature, tranny temp won't change cuz its tstat opening is rated somewhere around 96c. I just wanna lower that somehow.

I need around 85c. tranny feels MUCH better at those temps.

I’m not sure what you want or where you’re getting your figures from, but if you want your transmission to be at around 85°C then an 86°C transmission thermostat is only 1°C hotter.
And bear in mind that an 88°C engine thermostat is the temperature of the engine outlet, not the temperature in the bottom of the radiator which is generally around 10°C cooler (depending on the application, ambient temp, airflow, capacity of the radiator etc.) which is where the transmission heat exchanger is situated.
A 75°C transmission thermostat will result in the transmission temperature not being stable and fluctuating which is not ideal for smooth and consistent operation and gear changes.

[TiesTorN]

I’m not sure what you want or where you’re getting your figures from, but if you want your transmission to be at around 85°C then an 86°C transmission thermostat is only 1°C hotter.
And bear in mind that an 88°C engine thermostat is the temperature of the engine outlet, not the temperature in the bottom of the radiator which is generally around 10°C cooler (depending on the application, ambient temp, airflow, capacity of the radiator etc.) which is where the transmission heat exchanger is situated.
A 75°C transmission thermostat will result in the transmission temperature not being stable and fluctuating which is not ideal for smooth and consistent operation and gear changes.

no.

- thermostat starts to open at 86c. that means the actual temp will be around low to mid 90s
- 88c (also starts to open, engine temp is actually around 95c) engine thermostat means the fluid circulating inside the engine will be 95c. it doesn't mean the fluid inside the radiator will be 95c. it's cooler than that while the bottom of it will be much cooler like 50-60c.

[jicaino]

Yes, my posts gost deleted. You don't want your tranny ATF temp lower than 80ºC. It kills the tranny life and the fuid life. You don't want it hotter than 90º on city traffic, nor beow 80ºC cruising HWY or in winter driving. The pre- TU setup does that.

[TiesTorN]

Yes, my posts gost deleted. You don't want your tranny ATF temp lower than 80ºC. It kills the tranny life and the fuid life. You don't want it hotter than 90º on city traffic, nor beow 80ºC cruising HWY or in winter driving. The pre- TU setup does that.

that's what I'm trying to do actually, but I heard that pre-tu setup is usually not enough for that. I heard that it keeps the tranny between 90-100c.

what temps are you getting while driving? can it really keep the tranny between 80-90c ?

[jicaino]

Been running this setup for quite some time now. It's what you're seeking for. No pathologically lower temps on roadtrips, no overheat when drag racing or driving hard. As long as the car runs free over 30mph, the temp stays btwn 79º and 80ºC. Heavy city traffic in hot summer, hard passes or neck snapping from red light to red light in hot climate gets no higher than 92ºC Never seen anything abve 95ºC and that's when I was driving hard with no clutch fan in a particulary hot summer (new orleanish hot)

- - - Updated - - -

I see you're in turkey, I recommend the 88ºC thermostat for the cooling system along with either the M5 radiator or the hot climate version. No need to go fancy and expensive on bigger,with the 88ºC it's more than enough cooling capability. I purchased a very expensive and custom radiator (cooling system holds about 20liters now) but ended up replacing the thermostat before getting to the radiator. had I swapped the thermostat before ordering the radiator I'd have stayed stock, it was more than enough even running with no visco-fan.

- - - Updated - - -

Also it'simportant that you dismantle the whole front end and get good cleaning between the A/C condenser, PS/tranny coolers and radiator itself. There's a lot of debris that gets trapped there and it affects a lot the cooling performance.

[TiesTorN]

thx for the answer.

yep... I have the hot climate version radiator which has considerably larger water capacity than the original.

front end dismantled and cleaned 6 months ago, that's when my hot climate radiator was installed.

[balidawg]

just gut the unit and have it run open

This is what I did on my E46. The before and after logs of coolant temp, oil temp, and ATF temp were pretty close for normal driving. I just got tired of that t-stat breaking every time I pulled the ET.