Heater core HVAC delete

[VicS5]

Looking for guidance on coolant line re-routing for deleting the heater core from an S65 car. Other platforms employ block off plates and plugs, but the S65 has coolant routed from the head to the transmission to bring the DCT up to temp more rapidly.
I’ve seen many recommendations to avoid looping the heater core supply and return lines, but I can’t find much info on the S65. All kits and most information seem to be related to other platforms. I obviously don’t want to ruin my engine while chasing 20 lbs.
Hoping there are other similarly afflicted fools here trying to “add lightness” who have already been down this path.
Thanks.

[roastbeef]

i'm interested in the same.

is there a safe DIY way of taking out he freon? hold my breath and turn on a fan?

[VicS5]

I had the AC refrigerant removed by a local shop in a safe, environmentally conscious way.
One small step to balance out getting 7 mpg and destroying 4 tires in as many days.

Or you could huff it.

[VicS5]

Looks like the coolant exits the engine at the back of each cylinder bank into metal tubes that join and feed a single hose running to the DCT heat exchanger. Return line from DCT runs to auxiliary water pump, which then feeds supply to heater core through the bulkhead.
Return line from heater core runs straight to the return pipe to primary water pump.

I don’t see anyplace in the loop where there is opportunity for mixing of return from the DCT and return from the heater core. Rather it is a single continuous loop, and all coolant flows through the heater core before returning to main pump. I think the main role of the auxiliary pump is to augment flow to the heater core when at low RPM so the cabin still gets heated when in slow traffic. Heat delivered into the cabin is determined mostly by what the fan extracts, not by volume of coolant delivered.

Bottom line: I believe the coolant flow is a single continuous loop once it exits the back of the engine. Looping in a U-shaped bypass of the heater core (aux pump straight to main pump return line) will have no effect on cooling, except for the heat that would have been shed to the heater core. I suspect the auxiliary pump can be removed because it will never be activated by a call for heat at low RPM from an HVAC head unit that doesn’t exist, but I’m not comfortable with that assumption.

I’d welcome any input based on concrete knowledge rather than my suppositions. Am I naive to think there is no other hidden parallel flow path within the engine that I might be shunting coolant away from by creating a bypass of the heater core?

[amg6975]

Another thought is do you really need the wateril warmer for the DCT in a track car?

I would guess not but I have no scientific data to back that up. I think there are aftermarket solutions for deleting it.

[TheStevo1000]

I'm also trying to figure this out, as I've removed the heater & AC from my track car. I contacted Bimmerworld, Turner Motorsport, and Condor, and the people there also weren't entirely sure...I would agree with the assumption that the aux. coolant pump could be removed and the lines looped together. If the entire HVAC system is gone, would the aux. pump ever turn on? I don't think it's always on, right? One annoying problem is the hoses going in and out of the heater core seem to be different diameter, so I can't just connect them with a standard tube/pipe.

[VicS5]

I ended up installing a loop between the aux water pump and the hard return line. It’s 19mm on both ends, so a 19mm 180 degree bend hose works. The ends of the 2 hoses that attach to the heater core at the firewall are different sizes, but the other ends of those 2 hoses at the aux pump and the return line are the same size.

I didn’t remove the aux pump or bypass the loop to the DCT. Looks like temp sensors in the transmission control the aux pump, so even removing the full HVAC system wouldn’t stop the aux pump from running. See DCT info details here.
https://www.m3post.com/forums/attach...4&d=1317583307

I brought it up to temp in my driveway and all a seems stable and flowing well. Will be on track at WGI Monday and Tuesday to give it the full test.

All in, shed over 80lbs this winter.
AC pump, condenser, and lines.
EVAP system delete
SAP delete
Rear parcel shelf delete
Heater core delete
Washer reservoir and fluid
BW CF headlight blanks
Rear O2 sensors and extension wires, brake wear sensors, and various other metal bits and and further wire thinning

[TheStevo1000]

OK, thanks for sharing the great info. That's good to know. And that makes it pretty easy to just install a loop hose.

Ya, I've been weighing all the parts - then entire HVAC system and all related parts is around 39 lbs!

[calicoupe]

@vics5 Thanks so much for this post - the only info i can find on heater core delete for s65 motor. I'm also trying to determine if looping those lines vs blocking off both is the best path. Curious if after your track events you noticed any increase in water temp with the loopback? I'm a 6mt, so no trans oil heat exchanger in the system (hose goes straight from metal pipe on back of engine to the aux water pump, then same flow from there to heater core and back to primary water pump). Would seem blocking is ideal so hot water isn't bypassing the radiator right back into the motor, but as you said, i cannot find any diagrams of the coolant flow/passages for an s65 to know if there is anything else that would be affected by blocking that flow. This is a w2w race car and i race in Arizona, so coolant temps are already a serious challenge and can't really afford any increase in temps (i have had to turn the heater on during some races when it's 100+ but i find it reduces water temps max 3-4 degrees and gets me maybe 1/2 more lap so would rather remove and reduce weight and complexity)
Thanks!

[VicS5]

I have not noted any change in coolant or oil temps, but I also replaced the radiator with a do88 unit at the same time. Everything is working fine with the bypass loop installed, including through a 90 degree day at Palmer in June.

[calicoupe]

Awesome to hear. Thanks so much for the quick reply and thanks again for the post!
I too have the full do88 cooling package which has substantially helped. I use to get ~10 minutes of full racing in 90+ weather on stock cooling before hitting limp mode and having to back out a bit each lap to finish a race (~224F water temp), and I can now finish a 20min race hitting around 220F water temp.

[VicS5]

I used this hose to create the bypass loop. Had to cut one arm to make it shorter.
HPS 19mm 180 bend

[roastbeef]

so i'm thinking through this procject and i think you can simply bypass the auxilary pump and get rid of it. all it does is divert fluid to the heater core to heat the cabin.
the existance of the auxilary pump leads me to believe the entirety of those associated lines aren't necissary, but i'm not 100% sure.
if they were necissary for correct function, i'd imagine they would be pressurized enough during normal operation to not need an auxilary water pump.

anyone have any pics of their bypass of this system?

i'm watching some s65 rebuild videos and its giving me a lot of ideas... i'm planning on an electric power steering pump and that should allow me to get rid of even more forward weight in the car... there are two pulleys (one stationary and one tension) that you can get rid of, plus the power steering pump and a/c compressor. i'm also eyeballing the water pump pulley to have it remade in the same size, but less weight, as well as the main crank pulley. the forward most belt gets completely eliminated, and you can have a custom pulley made that eliminates that mass by converting it to a single belt pulley.

[Redd]

I believe the aux pump also sends coolant to the DCT heat exchanger.

[VicS5]

Originally Posted by Redd

I believe the aux pump also sends coolant to the DCT heat exchanger.

Yes, it does. See previous post with link to the DCT documentation.
https://www.bimmerpost.com/forums/sh...php?p=31076551

[roastbeef]

i forgot about that... thanks guys. reading up on it, it serves as a thermostat, as well as an oil to liquid cooler. i guess we can't touch it.

[roastbeef]

Originally Posted by VicS5

I used this hose to create the bypass loop. Had to cut one arm to make it shorter.
HPS 19mm 180 bend

are your using it as a "U?" My car has a hose that comes off the secondary water pump and goes almost straight into the firewall, then when it comes out it makes a hard right to go behind the engine block. it seems like i need a right angle hose rather than a U.

[amg6975]

The aux pump pulls coolant from the back side of the heads and then eventually returns it into the normal path of coolant at the radiator. I'd be concerned about the lack of flow where it pulls from without it.

If you're manual though, going directly from the back side of the head to the pump and bypassing the heater core should work just fine.

[roastbeef]

right, i'm not trying to get rid of it. i had the thought, but it was based on my own lack of misunderstanding.

[VicS5]

Originally Posted by roastbeef

are your using it as a "U?" My car has a hose that comes off the secondary water pump and goes almost straight into the firewall, then when it comes out it makes a hard right to go behind the engine block. it seems like i need a right angle hose rather than a U.

I tried to get pictures for you, but it’s tight, all hidden under the air box.
There are 2 hoses attached to the auxiliary pump. One is a return from the DCT, attached to the lower port in the pump. The other, attached to the upper port, normally runs through the firewall to the heater core. The return from the heater core then attaches to the metal pipe that is on top of the frame rail, eventually connecting back to the water pump, with a Y that splits off to the coolant overflow reservoir.

The loop I introduced connects the top port on the aux pump directly to that metal pipe return line that runs up to the front of the engine, bypassing the now-removed heater core.

Picture 1 shows firewall block off plate and the blue hose coming from DCT running to lower port on aux pump.
Pic 2 shows aux pump.
Pic 3 shows the “U” from upper port on aux pump to metal return line going to front of engine.
Pic 4 is at front of engine

[kolosy]

related to this -- is there any issue with taking out the HVAC control module itself? The part that sits in the dashboard? I ran across a post somewhere that that's somehow tied into engine temp management also.

[roastbeef]

Originally Posted by kolosy

related to this — is there any issue with taking out the HVAC control module itself? The part that sits in the dashboard? I ran across a post somewhere that that's somehow tied into engine temp management also.

Yes, it has some control over the efan. With out the controller, the efan is said to go full blast. There is a work-around with programming, but that is the end of my knowledge about it.