DCT Cooling circuit changes for track-only cars

[mikentosh]

Had the input shaft seal on my DCT fail while out at Buttonwillow this past weekend...lots of fluid along the underside and the transmission is now out of the car. Using this as an opportunity to reseal the whole trans and freshen the cooler lines and thermostat.

This opportunity got me thinking about the engine coolant <-> DCT oil heat exchanger, and if it's necessary on a track only car. I feel like keeping those circuits separated would be good, so spiking temps in one wouldn't take out the other. I can deal with elongated warm-up times, as I already face this with the engine oil diverter valve installed.

Thinking about using one of the aftermarket adapters from the transmission to AN lines, into a standalone oil thermostat, and then onto the front cooler in the bumper. But I'm not sure that the coolant exchanger is even used once the factory thermostat opens up, so maybe it's fine as-is. Would be nice to declutter some of the coolant hoses though.

[amg6975]

I've been thinking about this a lot recently and will probably try something after my next track event. I think that the cooling/heating situation of the DCT thermostat has three stages:

1) Heating oil with coolant
2) Cooling oil with air
3) Cooling oil with air and coolant

The third point is the key.

I also am looking for ways to just get more heat out of the whole system, oil, coolant, trans. It seems like the coolant loop is a good opportunity for improvement as stock it goes:

Heads > DCT > Pump > Heater Core > Return

It never once goes through a cooler of any sort, unless you're blasting the heat (which I've found does help things.)

My idea involves using the PPK2 water radiator from a 1M and changing the routing of this fluid to be:

Heads > Heater Core > Pump > Cooler > DCT > Return

Most of this can be achieved with off the shelf OEM parts, including the additional rad and ducting. My car is a 1 series but the 1M and M3 are the same between the bumper and wheel wells so the rad and duct should fit an M3. The bottom snorkle of the intake will need to be removed so it pulls air from behind the bumper cover, but that's how my car has always been.

My theory here is that my heat will still work the same as a manual car, the cooler will remove heat from the coolant when the DCT is in mode 2 above so the return coolant temp will be lower and help in overall engine cooling, and in the infrequent times the DCT needs to step up to mode 3, the coolant will be much cooler and able to recover the DCT temps faster. The only sacrifice is DCT warm up time, but that's not a big deal on a track car.

I have a track event in two weeks I'm going to get data on temps, warm up, cool downs, etc. Then plan to make that modification and head back to the track to compare data.

[roastbeef]

alex miller and i were having a conversation about this. he believes we can get rid of the secondary water pump and just connect the lower hose coming from the dct heat exchanger to the metal tube that runs along the frame rail. (we both have dct cars with hvac deleted)

i'm not sure about completely isolating the two... i think the liquid/liquid heat exchangers for the dct and engine is intended to do a few things- get the get the dct fluid up to temp in cooler weather, and controlling the dct fluid flow to the main dct heat exchanger.

[amg6975]

Yeah there was a Facebook discussion about eliminating the pump that a few people (including Alex) chimed in that they successfully run without it. Still sketches me out a bit and I don't see a good reason outside of possible reliability concerns to eliminate the pump.

The exact function of the DCT heating/cooling/? loop is a bit of an enigma. I've heard people say that when their pump dies (and presumably blocks the flow) the DCT will start to overheat, which leads me to believe that the coolant does do some form of cooling, I'm just not very clear on when and why, and how the air/oil cooler plays into that scheme.

My assumption is if the DCT temp gets too high it will use the coolant loop to try to lower the DCT fluid back to a safe level using the [hot] coolant. Just seems odd, and why I'm thinking cooling that coolant pre DCT would probably be a good idea.

I intend to a more scientific study on this once my upcoming HPDE is out of the way to see if there's a configuration that's more beneficial to the track crowd at the expense of "street manners."

[tdott]

Interesting topic, would be good to confirm some of the assumptions about how the system actually works.

Like you, I assumed that when DCT temp gets higher than coolant temp, that DCT heat exchanger would help to cool the DCT in some way in addition to heating it up.

[mikentosh]

I ended up putting everything back in OEM configuration with a fresh DCT thermostat and lines to the coolant/oil exchanger, and had it back out for a busy track weekend without increased temps.

One thought I was having is around the accessory pump activation...assuming the DME controls it, but wondering when it gets activated? When the heater is on? When the DCT temp increases? Would there be benefit by having it run all the time while on track to keep fluid cycling?

[bigjae1976]

The aux pump has a check valve in it to prevent the heater core loop draining back and creating an air pocket.

You'll see the common thread - I drained my coolant system, refilled it and now it is overheating! It is because some of the coolant drained out of the heater core line. As soon as they turn on the heater core loop it starts circulating air through the coolant system. As soon as they remove the expansion tank cap and turn on the heater...it fixes the problem.

And the pump only turns on when the heater is on. So no, you don't need the aux pump to have adequate flow.

[tdott]

Originally Posted by bigjae1976

And the pump only turns on when the heater is on. So no, you don't need the aux pump to have adequate flow.

I think he is asking if the aux pump ever turns on to circulate coolant when the DCT gets hot, or is coolant always going thru the DCT exchanger without the aux pump on?

Additionally I was wondering if the DME turns on the AUX pump, during the cool down cycle when the engine gets really hot then turned off, we know the fan turns on, but since it has an aux pump, circulating coolant would also help cool down the engine. I'm just not sure if the S65 does that.

[bigjae1976]

Originally Posted by tdott

I think he is asking if the aux pump ever turns on to circulate coolant when the DCT gets hot, or is coolant always going thru the DCT exchanger without the aux pump on?

Additionally I was wondering if the DME turns on the AUX pump, during the cool down cycle when the engine gets really hot then turned off, we know the fan turns on, but since it has an aux pump, circulating coolant would also help cool down the engine. I'm just not sure if the S65 does that.

Didn't think about the engine off scenario. I'm sure ISTA or a diag tool can see when the aux pump is on.

[amg6975]

Originally Posted by bigjae1976

Didn't think about the engine off scenario. I'm sure ISTA or a diag tool can see when the aux pump is on.

This is one thing I'm going to investigate a bit deeper. I know that one of it's purposes is the residual heat feature where the interior heat works for a bit after you shut the car off, this is thanks to the aux pump.

Not sure when else the pump is on/off and how much, if any does it restrict the flow if it's off.

[Redd]

It's not true that the aux pump only runs when heater is on. My car lived the first 5 yrs of its life in the UK and came to Malaysia with 40k kms. The past 10 yrs / 120k kms in Malaysia the heater has never been switched on as it's always hot here, so a/c only 100% of the time. Yet I got A6D1 aux pump error couple years ago and had to replace the aux pump. When I opened up the old aux pump, the carbon bushes were completely worn down and there was carbon dust all over the insides. So the aux pump definitely is still working even when heater is not switched on.

[VicS5]

This post contains some details about the coolant aux pump and its role in managing DCT temps. There is also a link to the BMW documentation on the DCT.
https://www.bimmerpost.com/forums/sh...php?p=31076551
See page 45.

[Redd]

Hmm since it's perpetually hot here, I'd also be keen to know if it's possible to eliminate the heat exchanger and aux pump without any errors.