Slight weeping between heater core and heater valve - replacing the o-rings?

[mike.bmw]

I had my center console out today to fix a crack and noticed that the connection between the heater core and heater valve is weeping (very minimal, not even getting on the carpet). I know there are two o-rings here (# 64118377824). I'd like to replace those as there are no other leaks and everything functions properly.

How much coolant will come out when I disconnect those parts to replace the o-rings? Any tips to avoid getting coolant on my carpet?

What kind of oil should I lube the o-rings with?

Do I need to disconnect anything in the engine bay to separate those parts enough to replace the o-rings?

Thanks!

[Albie325]

Hey Mike,

If I were you, I'd try and disconnect the coolant hoses on the engine bay side leading into the heater valve to try and drain as much coolant as you can prior to disconnecting the valve from the heater core. Even then, I'd estimate about 1/2-1qt of coolant will come out of the heater core once disconnected. It was a messy job, I'd lay down plenty of towels and have a paint mixing cup or something under the heater core valve ready to catch as much coolant as possible once you pop it off.

Not sure the m42 "mess under the intake" heater core hoses are the same as for the m20, but I imagine they converge to connect the same way leading into the heater core. Mine had the heater valve coming out of the core, followed by two small aluminum tubes that are secured to the HVAC box with a small bracket, and the aluminum tubes go through the firewall through a rubber grommet to connect to the coolant hoses in the engine bay just next to the fuse box. I think the only thing you'd have to remove to have enough wiggle room to get the valve off the heater core is the bracket holding the two aluminum tubes to the HVAC unit, it was only 1 phillips head screw.

Only pic I could find from when I had it all out of the car:

[reelizmpro]

No need to disconnect the hoses in the engine bay. All you are doing is disconnecting the 3 - 8mm bolts at the core and the single phillips screw securing the pipes to the HVAC unit. Lay down towels and get a tall cup to catch the coolant. Just pull the pipes away from the core and change the O rings. How old is the core? It may be worth your while to inspect it and maybe swap it out but that's upto you.

[mike.bmw]

Thanks Albie325 and reelizmpro .

I'm not sure how old the heater core is, but maybe I'll replace that while I'm in there (only $38). The only thing that scares me about this job is making a huge mess and getting coolant all over the interior.

Here is where the coolant is weeping from:

20200513_143957 by mike.bevels, on Flickr

Here is the HVAC unit. I'm not sure if 64/11 refers to a date code.

20200513_151230 by mike.bevels, on Flickr

I'll order the o-rings, some extra hardware, and the heater core today.

Do the o-rings seat inside the heater core or do they just slip onto the aluminum pipes? What is best to lube them with (regular oil, vaseline, etc)?

[roguetoaster]

Use some sort of fairly inert grease on the o-rings. I generally use Plastilube or something similar.

The gaskets slip over on all but one connection IIRC.

To capture coolant spills take any piece of thin metal, bend it in to a shallow v, or any other shape that will work for you and put it in place between the coolant pipes and your collection device when you break the connection. Alternately, rags and plastic sheeting work to protect the carpet.

[mike.bmw]

Use some sort of fairly inert grease on the o-rings. I generally use Plastilube or something similar.

The slip over on all but one connection IIRC.

To capture coolant spills take any piece of thin metal, bend it in to a shallow v, or any other shape that will work for you and put it in place between the coolant pipes and your collection device when you break the connection. Alternately, rags and plastic sheeting work to protect the carpet.

Thanks! I've been thinking through this and I think that's what I'll do (pastic sheeting and a make-shift "V" funnel to direct the coolant).

Without draining any coolant or disconnecting anything undert the hood, my plan of attack is:
- remove the airbag-car specific metal bracing (knee bolster, etc) to gain easier access to the heater core
- remove the E-shaped bracket on the coolant pipes near the firewall (under the dash)
- remove the duct above the heater core
- remove the 2 screws holding the heater core in place
- wiggle the heater core out slightly
- remove the 3 screws (with square nuts) attaching the pipes/valve to the heater core
- separate the pipes from the heater core
- catch the coolant
- lube and replace the 2 o-rings (I'm on the fence about the heater core... if it ain't broke?)
- button it all up, let the car warm up for a while, check for leaks, etc....

[roguetoaster]

Just replace the core now rather than going back later. If you do replace the core you might want to pick up some quality weatherstripping to replace the cheap foam sealing strips that come with some cores.

I would also consider removing the engine bay hoses and lubing the grommet where the pipes pass through the firewall as it can be somewhat frustrating if you have extra resistance to movement in the restricted work space of the footwell. How impactful that would be really depends on your flexibility and level of patience.

[mike.bmw]

Thanks everyone! Parts ordered. :-)

[D.Martijn]

How does you valve look? Might be a good time to replace that one as well since they also tend to leak.
A new one it rather expensive, but I decided to buy one anyway since I didn't want to deal with this hassle twice.

[mike.bmw]

Closing the loop on this. Yesterday I replaced the heater core, valve, and o-rings. Details here: https://www.r3vlimited.com/board/for...07#post9927307