mystery water leak e30 m42 318is

[318lotis]

i am having to to add coolant ervery few days and have recently notice my floorboards are wet under the carpet, but my heater works good, how would one check for leaks in heater core??thanx

[DesktopDave]

Pull the knee bolster & lower trim, unscrew the heater core cover and look carefully.  You should strongly smell coolant if that's where it's coming from.

e30's have a habit of rusting in the lower corners of the windshield seal...there is a little pinhole drain and tape seal that fails over time and lets in a surprising amount of water.  Might be a leak somewhere else like the heater plate, coolant tubes, etc... (hopefully not your head gasket) and you just have water in your driver's floor pan.

[318lotis]

thanx, i also have dripplets of water falling off transmission and no signs of any leaks under hood.

[DesktopDave]

Did you check hose 23 too in this RealOEM diagram?  I'll bet you already did, so I'm a bit puzzled.  That's an odd way for a leak to happen.  I can't think it'd be anything but the core.  Keep in mind there are two cores for these cars, the metal valve one and the plastic valve one.  I'm not sure which years/models have either one.  Both are on this page of diagrams.

Maybe you have a clogged drain?  There are two on either side of the transmission tunnel from the bottom of the heater housing.  You can see & check them both if you pull the center console, they're just little tubes sticking out of the tranny tunnel.  They just pull out off the lower HVAC housing, under the heater core.

[318lotis]

i have 1991 e30 318is, i noticed my 23 hose is bent probably the wrong hose for this car, too long, i plan to keep watching, the driplets of coolant are dripping of transmission and the carpet is damp, but i cant find a single drop in engine bay.

[DesktopDave]

I'll bet it's the heater core then.  Pull the covers off and watch it while it runs.  Those HVAC drains might channel some of the coolant down & out of the car, probably why it's on the transmission too.

[318lotis]

thanx for reply Dave, i will follow up with an update once we check the heater core for leaks.

[Cobra Jet]

Check the double hoses coming off the firewall on driver's side...  These are the heater core hoses.  Sometimes, if they are seeping, the drips or leaks will be UNDER the hoses, which will be very hard to see from ABOVE the engine bay.  You will need to take your hand/fingers and wipe under the hoses, if you have any blue (BMW coolant) or green (standard coolant) on your hands or fingers, then you have a leak.  First try tightening up the hose clamps, rinse everything and keep monitoring.  

IF the leak persists, then you have an issue w/ the heater core as noted a few times in this thread.

The other areas to be concerned w/ as far as leaks:

head gasket - sometimes they can fail at any point around the perimeter of the head, including the back part of the head. Get the car safely on ramps and using a light, shine from the bottom up all around the base of the head - you should be able to spot any leaks OR coolant staining on/along the base of the head or sides of the block in this manner.

engine freeze plugs - check for coolant staining

engine drain plusg - again, check for coolant staining

if your M42 is stock and still retains all of the medusa of factory hosing/vacuum lines under and around the intakes, you will need to throughly inspect these hoses - especially the hoses that carry coolant...  ANY ONE of those hoses can leak.  Also be sure to check the nipples that go INTO the heads to which those hoses attach to as well - those factory nipples are KNOWN for corroding and rotting out, which will also be a source of a coolant leak.

heater core - pull up the center console and you will be able to see the core.  The core can leak from the center core itself due to age, corrosion, etc.  It can leak from the primary tubes that go through the firewall, OR it can also leak from the valve that is attached to it.  Sometimes a core will not emit the coolant odor, so you can't rely on just smell alone...  Pull the center console and EXAMINE the core physically from all sides and more than likely, you will see exterior coolant staining on the core itself OR along the trans tunnel under the carpet.