E36 M3 Losing Coolant

I'd rather ask this question here than on one of the forums. I bought a 1997 M3 a few weeks and ~850 miles ago, did a PPI, etc. Though everything was good until last week when I get the coolant low warning light. No prob, the PO mentioned that the coolant is due to be replaced. Topped it up with distilled water and got the light again almost immediately.

Since then, I can't keep coolant in it - I've gone through 2/3 gallon of distilled water in a few days and I get the light every time I drive the car.

I pulled the undertray off the car and I can't find an obvious leak.

The oil appears fine (just changed it, no white sludge).

The coolant appears free of oil.

When warming up with the heat on, the air starts to blow warm within a few minutes. The car never runs even a tick past the halfway mark, there's no smell of coolant from the vents.

When the car's warm, there's a distinct sweet/coolant smell from the center front engine bay area right by the fan. I can't see a leak, but I can smell coolant.

I tried bleeding the system and topping it off on Sunday - warmed the car up with the radiator cap off and the bleed plug undone until at operating temp, filled until the overflow bottle was nearly full. Drove it for a bit and the light came back on. Again, this is total of about 2/3 a gallon in 3-4 days and not a lot of driving. I did notice that if the car was revved with the rad. cap off and the bleed plug undone, coolant would shoot out the bleed plug. Not sure if that's normal.

At this point I'm thinking HG, though there isn't any white smoke out the exhaust that I can see and I can't see any contamination in the oil/coolant. One thing's for sure, this car's gone through a ton of distilled water in a very short period of time.

From the receipts the PO gave me, the entire system was gone through in 2005 and ~20k miles ago. I planned to do everything all over again, but with the way it's losing coolant I'm worried it's something bigger than that.

Any thoughts? I ordered an oil analysis kit from Blackstone and a friend referred me to a coolant hydrocarbon test kit. Beyond that, I have no clue where all that water's going.

check on the back of the block for a coolant trail, next to the bell housing. More than likely a headgasket. Mine needed one, chick im with is doing the same, but hers is a 95 M3... start there...

A couple of things that I've run into:

• Coolant expansion tank cap - I had a very slow coolant leak that was driving me nuts, it turned out the cap was faulty and would leak coolant when under pressure. Never saw any drops on the ground or any leaks, but it was obvious when I ran the car with the hood up. Replacing with a new cap fixed the issue.

• E36s seem to be notorious for being difficult to bleed, although I didn't have any issue. I followed Pelican Part's procedures, and had the front wheels on ramps to help get the air bubbles out.

• My radiator hose clamp on the lower hose was making ever so slight contact with the framerail, which was loosening up the clamp just enough to cause a slight coolant leak. Re-clocking the hose clamp and re-tightening solved the issue.

Really go through any plastic pieces and hoses, as the plastic in the cooling systems on BMWs is notorious for cracking.

Good advice - the cooling system's due for a refresh anyway, and it won't hurt to have everything new to eliminate all variables.

Oddly enough, I ran the car for 15 minutes yesterday while checking for leaks. Got to full operating temp and used zero coolant (coolant was at the same level cold before and after).

Check the water pump. Some of them start to leak from the bearing and the fan dries it on the hot block before it hits the ground. This is also the case for pinholes in the radiator.

Check the back of the head under the intake above the starter where heater hose connects.

I hate to say it but... before you refresh the whole cooling system... smell the exhaust and do a leak down test. The most common HG failure on an E36 is the webbing between the cylinder and the water jacket. It only takes one overheating. You don't see coolant because it goes out the tailpipe. This typically pressurizes the cooling system and pushes water out of the overflow drain too. If you leave the cap off and warm it up - do you see a lot of bubbles in the waterflowing thru the radiator?

Have you checked the thermostat housing? The plastic ones suck, people replace with metal...

speedblind wrote: Good advice - the cooling system's due for a refresh anyway, and it won't hurt to have everything new to eliminate all variables. Oddly enough, I ran the car for 15 minutes yesterday while checking for leaks. Got to full operating temp and used zero coolant (coolant was at the same level cold before and after).

Well, this is a positive sign.

They need to be bled well after a hose replacement or other repair... maybe the PO had an issue and just topped up afterward.

The best way to do it is to turn the heat all the way up, wait for the little motors in the dash to catch up then turn off the key. Elevate the nose... open the cap & bleed screw and keep filling SLOWLY until water runs out the screw without bubbles and the reservoir is full. Cap it. Drive it until its warmed-up. Park, cool, top up if necessary.

Thanks for the replies everybody. The car's still on jack stands (front elevated), so I'll give it a complete fill one more time using the Pelican method and then see what happens. I suppose it is possible that the coolant is a few years old and just leaked out slowly over time. Fingers crossed!

As for the exhaust, there's some water/condensation, but it doesn't smell like coolant. T-stat housing is metal.

Giant Purple Snorklewacker wrote:

speedblind wrote: Good advice - the cooling system's due for a refresh anyway, and it won't hurt to have everything new to eliminate all variables. Oddly enough, I ran the car for 15 minutes yesterday while checking for leaks. Got to full operating temp and used zero coolant (coolant was at the same level cold before and after).

Well, this is a positive sign. They need to be bled well after a hose replacement or other repair... maybe the PO had an issue and just topped up afterward. The best way to do it is to turn the heat all the way up, wait for the little motors in the dash to catch up then turn off the key. Elevate the nose... open the cap & bleed screw and keep filling SLOWLY until water runs out the screw without bubbles and the reservoir is full. Cap it. Drive it until its warmed-up. Park, cool, top up if necessary.

What do you mean by little motors in the dash catch up - do you mean until warm air starts coming out the vents?

E36 engines have a weak upper neck on the radiator. They commonly break off. I don't remember if you need to take off the shroud to see it. Stress the upper hose and see if a crack opens up on the plastic neck. The engines are super solid, it's either that, a plastic thermostat housing or a bad water pump impeller (but I bet a 97 with have had those parts replaced already).

Precisely how my S52 acted.........when the headgasket was toast!

speedblind wrote: What do you mean by little motors in the dash catch up - do you mean until warm air starts coming out the vents?

no, just enough time to open the valves to the heater core

Got it.

Picked up a block test kit yesterday and the coolant is free of hydrocarbons. I'm now wondering if maybe the coolant was just low when I bought the car and I've never properly filled/bled the system (I've been filling to the Kalt line, not filling/bleeding as described by the Pelican Parts process). Come to think of it, the car was a bit low on oil as well when I got it.

So, I guess it's time for one last attempt at filling/bleeding the system before I get too worried. Will still do the Blackstone analysis for peace of mind.

Thanks for all the suggestions. I'll report back what I find.

Update - filled the system and the light went away. Still losing coolant, though not at the rate I thought I was. A 30-minute, hard drive would put the overflow tank roughly an inch lower when fully cooled. Came back from a drive and noticed steam coming out of the engine bay. Popped the hood and found this:

I've never been happier to see a coolant leak in my life! Only downside is it's under the intake manifold. Poking around, there's a lovely little rat's nest of hoses and vacuum lines down there, so the manifold's coming off and it's all getting replaced. In a classic case of "while I'm in there", I'm biting the bullet and redoing the entire cooling system - new aluminum rad, t-stat, water pump, etc. According to the receipts, this one's a few years old, but only about 10k miles. No idea what level of parts were used, though, so might as well check it off the list and forget about it.

To those that asked, here are pics of the car from when I picked it up: