Does the Heater Core Drain Through Frame Rails?

[Cup1d]

So, there are a few threads on heater core replacement. Looks like the best way to get about my '91 US Spec 850 is to remove the dash. Yay... Effin' perfect.

My question is (before I get 4 hours in...), does coolant leak through the frame rails?

1014170700a.jpg

That's certainly where mine looks like it is coming from. There appears to be a little on the sway bar, but it mostly travels down (inside?) the driver's side frame rail. Initially, I thought it was the aux water pump/valves, but they are bone dry. <- Whatever "bone dry" means; not wet.

Wish me luck.

Other sources of people who had just as much fun as I'm about to have:
https://www.bimmerforums.com/forum/s...t=coolant+leak
http://www.meeknet.co.uk/E31/E31_Hea...eplacement.htm
https://www.bimmerforums.com/forum/s...t=coolant+leak

[Cup1d]

A few additional notes:

-No foggy windshield
-No smell of coolant in the cabin
-No wet carpet

1014170911a.jpg


Looks like it starts here and then trickles down.

1014170913.jpg

Just looking to find out where the real drain is.

My next step is to put it on stands and investigate further. I will look at the aux pump more, but I doubt it's that. Leaning towards the core at this point.

[jclausen]

No heater hoses rear coolant hoses leak at the rear also the valley pan could leak. The cross over pipe, ect. I would get a good independent shop to verify your findings because removing the heater core is probably the worst repair to do. The coolant is just finding its way on to the frame rails

[Cup1d]

Yeah. I just replaced valve cover gaskets and sealed up the intake manifold gaskets last week. The crossover pipes looked perfect when I inspected. It's really a hard call because I bought the car just over a month ago. Yep. I'm that guy.... I wish I had more time to drive it around *before* I tore it down, but the thing was bleeding oil.

No worries, it's only time and money, right? *sigh*

From looking at everybody else's threads, I think I can get the cover off and inspect the inside of the heater core through the center console *before* ripping the dash out? I *should* be able to tell if the inside is wet. That's the initial goal!

Such a common problem and yet, seemingly random that it's hard to diagnose.

More to follow...

[jclausen]

It is the worst job, if it were me I would get a second opinion, because you have to remove all those plastic trim parts and you know that there going to break, we just did a evap core in a e70 x5, ton of work

[dragon850]

It is NOT the heater core, your aux water pump may have a broken inlet. If not check all the hoses at the back of the engine. If not then it's a cross over pipe, or a water jacket cover at the back of the engine. In that order.

[Dr. T]

What about checking up along the drivers side firewall...especially under the water valves/aux. water pump assembly and rubber associated heater hoses along the firewall.

I once had the rear “Y”pipe burst and shoot hot steam all over the rear firewall and up through the back of the hood/windshield while at a red light. Made for quite a show....

[rogbmw]

I would second looking at the Aux Water Pump and pipes. I bet it is coming from there. Especially since you have no antifreeze smell in the cabin or fogging windows. Plus, when my heater core puked, the antifreeze drained into the cabin as the core is in the heater housing.

[72tpik5]

What they said. If you don't have a foggy windshield, or no smell of coolant inside, it is not the heater core.

[BMSman]

Are you sure it is coolant?

The Brake booster will leak down inside the drivers frame rail especially if the booster is leaking at its front seal. It collects in the rubber boot and seeps down the firewall.

Otherwise lift the heater solenoid and inspect rear hoses.

[cartoonz]

I agree it likely is not the heater core.
For future reference though, you DO NOT have to remove the dash on a '91 to replace the heater core. Sure, it is still a pain in the butt, just not nearly as big a pain as with the later cars with the extra crash bar...

[Cup1d]

Okay guys.

Walk of shame time.

You are right. It is *not* antifreeze. I got a chance to take a closer look and found this:

Paint coming off...right underneath the spaghetti factory of brake lines...and in the worst way.
1014171731a.jpg

It's this freaking thing. (ASC-T, better known as the Hydro)

1014171732a.jpg

Has to be Pentosin? Thought it was brake fluid? (Confusion all around!) I cleaned up the area and was able to get my finger under the ASC and it came out wet. Crap!

Any good write-ups on replacing/fixing it?

Here I am thinking getting after the Heater Core would be difficult...

[dragon850]

Okay guys.

Walk of shame time.

You are right. It is *not* antifreeze. I got a chance to take a closer look and found this:

Paint coming off...right underneath the spaghetti factory of brake lines...and in the worst way.
1014171731a.jpg

It's this freaking thing. (ASC-T, better known as the Hydro)

1014171732a.jpg

Has to be Pentosin? Thought it was brake fluid? (Confusion all around!) I cleaned up the area and was able to get my finger under the ASC and it came out wet. Crap!

Any good write-ups on replacing/fixing it?

Here I am thinking getting after the Heater Core would be difficult...

Put your hand under the the brake booster, there is a weep hole there and check if it's leaking. Alot of times the brake booster leak is mistaken for ASC+T pump leak as brake booster can leak directly onto the ASC+T pump and make it seem like it's leaking. If the Brake booster is not leaking I have good replacement ASC+T pumps available. Removal is not that complex, you will need to unbolt and remove the brake booster+brake cylinder first to get to it.