Ive been doing loads of research recently about trans faults and failures, most of which were from overheating, the bottom section of the rad being a common cause. Now I have also realised there's a lot of conflicting opinions on the cooling set up of the BMW engine, I understand a lot of money and time was spent developing the system but it does suffer when getting on a bit on higher mileage cars, and I believe adding a little something extra to help cooling can't be a bad thing? I was thinking along the lines of an aux inline cooler, but then the more I looked into that it was flawed by the fact the water cooler it has would probably just warm it back up, this is where I started to have a think, it's obvious that a water cooler is the best option because of its ability to take away heat when in slow traffic etc, but the fact the water runs at around 105deg which IMO is a tad hot, the water cooler if I'm right opens around 80deg so surely that's the temperature BMW wanted intended to keep it around? If not then surely it would open later? I think I found some of RRPhill temperature logs showing quite high temps before it stabilises, now if I'm honest I don't know what the perfect temperature is for the fluid to operate but I would assume 80deg is better than 100plus so here's my idea, run a small rad upfront with an electric pump that is triggered by the cooler thermostat opening so instead of sharing the engine coolant it would have its own little system just to supply the cooler with cool water. Now I know most people will start shouting BMW wanted it run this way and that money should be spent on keeping it all standard and in good working order, which I will be doing, but me being me I like to give things a go! I don't think this is a complicated setup and wouldn't cost that much, and would guarantee a constant cool temperature of the trans fluid.
So what's youre thoughts? Be nice

Buy an oil cooler with inline stat set at say 85'c as i know they exist and just use that. better than worrying about more water circuits and electrics  FFRR MY06 facelift With TDV8 Alloys Zeros/ATR's
Mantec Sump Guard, Rigid Load liner, MY10 BT upgrade.

You mean instead of the water cooler? This is another option but it then goes back to no cooling at standstill, but then again every other auto I have had has coped fine with a standard air cooler, even my r34 skyline running 400bhp

Just sit it infront or behind the current oil cooler so it gets good airflow on the move. and if you really want airflow maybe break into the electric fan circuit and use something like a small 12cm PC case fan to pass air over it enough at standstill?? FFRR MY06 facelift With TDV8 Alloys Zeros/ATR's
Mantec Sump Guard, Rigid Load liner, MY10 BT upgrade.

A read of the web suggests that an optimal temp for transmission oil interns of preserving the fluid is in the 80 to 90 deg area.

Regarding air coolers, at stand still, how much does the box heat the fluid anyway? Can't be that much can it? . Just passing it through a cooler matrix exposed to the air must make the fluid temp drop a few degrees regardless... If the cooler is large enough, that drop must surely exceed the small heat up of the fluid when sat in neutral or D a standstill. Net effect being a drop in overall temp. V8 or else ...

Very good point mate, still cant make my mind up what route to go

Wanna hear something scary ?

Whilst tinkering with the Faultmate to clear some errors ( EAS stuff as usual ) I have a look at the transmission temps.

It had been a short run, the engine was unto temp and was idling in P for about 10 minutes.

Trans Oil temp: 90degC

Engine temp: 112degC



Ok - that was the reading the transmission was giving ... but feck me ... i've gotta get that temp down if it is that high. V8 or else ...

Fisha:
The temp sensor is inside the pan; 90C is a bit on the high side for pan temp,

RAVE isn't specific as to the cooler plumbing, saying only "fluid is pumped through the cooler by the pump."
Looking at the picture, it seems like the cooler return line goes into the pan.

Below 60C or above 124C, the ECU goes into "heat it up" or "cool it down" mode; this implies a fairly wide operating range. Other reading seems to indicate pan temperature of about 80C as "ideal".

RAVE discussed the "Thermostat - Fluid Cooler" in the repair section of the autobox.
The car's not home right now for me to go look under the hood.
I did not find any description of this thermostat as far as what temperature it opens and closes. Jim
2000 NAS HSE
2005 NAS HSE

fisha wrote:

Wanna hear something scary ?

Whilst tinkering with the Faultmate to clear some errors ( EAS stuff as usual ) I have a look at the transmission temps.

It had been a short run, the engine was unto temp and was idling in P for about 10 minutes.

Trans Oil temp: 90degC

Engine temp: 112degC



Ok - that was the reading the transmission was giving ... but feck me ... i've gotta get that temp down if it is that high.

Bloody hell that's hot I think the best way is to remove the cooler and replace with a conventional cooler, that way there's less heat going into the coolant and the trans stays at a more moderate temperature, as long as its big enough I can't see it being such an issue at standstill, not quite sure what the most efficient location would be though?

jim2RRs wrote:

Fisha:
The temp sensor is inside the pan; 90C is a bit on the high side for pan temp,

RAVE isn't specific as to the cooler plumbing, saying only "fluid is pumped through the cooler by the pump."
Looking at the picture, it seems like the cooler return line goes into the pan.

Below 60C or above 124C, the ECU goes into "heat it up" or "cool it down" mode; this implies a fairly wide operating range. Other reading seems to indicate pan temperature of about 80C as "ideal".

RAVE discussed the "Thermostat - Fluid Cooler" in the repair section of the autobox.
The car's not home right now for me to go look under the hood.
I did not find any description of this thermostat as far as what temperature it opens and closes.

I found out the hard way today which is the return I thought I read somewhere and also assumed it would be the pipe that's attached just above the pan on the passenger side of the engine, this resulted in about 5L of fluid being pumped all over the place It's actually on the selector side