Coolant/Heater Problem - The Unofficial BMW M5 Messageboard (m5board.com)

Stirocket · 2nd February 2009, 04:32

Couldn't find my specific problem in a search so I would like your opinions.

I was driving home last weekend on the freeway (at night) and accelerated briskly to get around some slower cars, suddenly alarms went off. The instrument cluster indicated the Batt light was on, the ABS light was on, then I noticed the coolant temp started to climb rapidly. I shut off the engine at 70 MPH and coasted to the next exit where I sat for about 15 minutes trying to decide what happened. I fired up the car and drove about 1/4 mile to a gas station as the temp started rising again. I shut it off and opened the hood, no problem was visible so I looked under the car. Coolant was pouring out around where the transmission is.

I had the car towed home, and just got a chance to work on it this weekend. The belt that drives the water pump and alternator had disintegrated. The pieces I found were hard brittle chunks of belt, obviously way past time to be replaced. I should've guessed that because the Batt light came on. So I got a new belt and put it on today. I put some coolant back in and fired up the engine, monitoring the coolant level in the expansion tank and looking under the car for leaks. No leaks initially, but as the temp came up to the normal range water started dripping out under the car about where the transmission is. So I jacked the front of the car up and put it on blocks so I could get underneath and find out what was leaking.

I found water leaking out of two holes about 3/4" diameter above and on either side of the transmission. The holes come from within the chassis and empty out above the transmission on either side. My guess is that the heater core (or plumbing to or from it) is leaking, and that there is a channel or ductwork that allows coolant to drain out of the car instead of inside the passenger compartment.

Does anyone have experience with a leaking heater core, and is that likely what my problem is?

Tks for your assistance...

Mark -

Dan Kelly · 2nd February 2009, 12:46

Hi, I've just had to repace my heater core - not a pleasant job!
The whole centre console/lower dash has to come out. The part wasn't that expensive at £140 but allow for 4+ hours labour.
My symptoms were the car suddenly steaming up and not clearing even with the air-con on full blast and leaking from the two holes you mention so sounds like yours is FUBAR. Sorry.

Stirocket · 3rd February 2009, 02:21

Tks for the confirmation Dan... I guess I'll pull it apart and see what I'm up against... Considering the condition of that fan belt, it might just be a bad hose.

Dan Kelly · 3rd February 2009, 12:05

No problem, unfortunatly there are no hoses on the inside of the cabin, just some metal pipework and the heater core. There are some O ring seals where the pipes meet the core, but if you've gone that far you might as well change the core anyway.

Stirocket · 4th February 2009, 05:52

Tks Dan, After reading your post I did some research and found that you're certainly right about the metal lines inside the passenger compartment. It's really a brilliant design by BMW as it makes the heater core the only likely element that can fail and cause coolant to leak in the passenger compartment. Since there is apparently ducting that channels the leaking coolant out of the passenger compartment to those holes over the transmission there should never be any coolant leakage inside the passenger compartment.

This is good news as now I have a better idea about what I'm up against. I'll report back when I have done some disassembly and know what's up...

Mark -

Matrixcode · 8th March 2009, 17:34

hello there ... I have same problem with the antifreeze but in this case i get antifreeze on my site ...drivers site ...anyone knows what could it be ...or as you said just open it up and change the heater core ?

IvanDias · 9th March 2009, 14:19

I had this exact thing as year or so ago, coolant appearing from above the gearbox. It was a failing heater matrix.

A kind member here sent me a photo similar to Dan Kelly's image above, but taken from the back seat. As it looked like someone had tripped a claymore mine in the footwell, I took a single glance at it and booked it into the garage!

They said they needed to disassemble the car (as per above pic) to get to the matrix, then order it as apparently BMW used 3 or so different types. They took it to bits on day one and and ordered the correct part and astonishingly BMW delivered it lunchtime on day two so they managed to fit it that afternoon! They had quoted a week.

If I recall, the labour was £150 and the total bill around £350. I know I would have broken lots of things had I tried to remove that centre console, so I chickened out and got them to do it.

Oily bits I can fix, plastic bits I break!

Kind Regards

Ivan

rmck · 10th March 2009, 14:33

just done the same job last weekend,
when i removed the carpets there was approx 25mm of water under them from the small rad bursting,
imo check under the carpets for signs of water just to be on the safe side!

Stirocket · 11th March 2009, 03:28

I really appreciate the posts guys... and I now know what I have to do but we've had freezing weather and snow since I started this thread, and I just haven't felt like crawling under the dash yet...

I intend to do a DIY with photos, so I hope it will be worth the wait for those who are waiting...