M50TU cracked head/headgasket?

[bubba966]

Car info is

1995 525iAT
6/94 build date
167,597 miles
Stewart water pump/low temp stat/factory stat housing installed about 1 year ago
Brand new rad & expansion tank


Friend says she thinks it's burning coolant. Exhibits white smoke when fully warmed up she says. She says she's also having to add 1"-1 1/2" worth of coolant to the expansion tank every day. Also says that it might be leaking as there's some small evidence of that under the car in the carport.

It's never overheated or even gotten over the half way mark on the temp gauge.
I checked the oil fill cap, no signs of coolant.
Checked the dipstick, no signs of coolant.
Checked the expansion tank, no signs of oil or excessive pressure from engine pressurizing the cooling system.
Exhaust didn't smell like coolant either.
But tailpipe had a small amount of white around the edge.

From her descriptions it sounds like it mostly happens on the freeway (the white smoke being visible). I didn't see any obvious signs of bad gasket or cracked head. But I'm wondering if it's there's a very small crack started in the head that's letting coolant into the combustion chamber at higher RPM's?

If the head is starting to crack would a compression or leakdown test show that? Or do you really need to pull the head to check that?

Do heads on M50TU's crack or blow headgaskets without overheating?

If cracked can it be welded up or fixed somehow?

Anyone have a spare M50TU head they'd let go for a reasonable price?

She wants to get this taken care of soon as she's got a new munchkin on the way that's expected to get here in about 2 weeks and would need the car for new munchkin transport. And she isn't afraid to get it fixed. But would rather know better what exactly (if anything other than a coolant leak) is wrong so that money just doesn't get thrown at the problem until something is fixed.

[bsell]

Time to consult with the spies of the combustion chamber, the spark plugs.

Pull all six and see what there is to see. If you find one, or more, very clean, as in 'steam cleaned,' you will have found what you didn't want to. Coolant getting into places it shouldn't, 'steaming' the plug and combustion chamber clean.

Applying pressure to the combustion chamber in a 'static' engine may show in the expansion tank if the head is cracked. It would take a pressure gauge in place of the cap, which would show pressure leaking from the leakdown test through the head or headgasket and into the expansion tank.

I kind of doubt your friend's car will show a problem this way as she hasn't blown up any cooling system parts yet. I figure she is leaking on the intake side of the intake or head, causing the always lower coolant level and the worriesome smoke.

Good Luck,

Brian

[Dave M]

Friend says she thinks it's burning coolant. Exhibits white smoke when fully warmed up she says. She says she's also having to add 1"-1 1/2" worth of coolant to the expansion tank every day. Also says that it might be leaking as there's some small evidence of that under the car in the carport.

With the info you've provided, I'd be hesitant to start down the failed head gasket/cracked head road if there are, in fact, signs of an external leak. This is coming from someone who has been through a cracked head on an M50 engine with similar symptoms. If you were noting prolonged cooling system pressure (upper rad hose feels hard well after system has cooled) then I would think differently. However.........

With regard to the white smoke, we've been commenting on the size of these exhaust systems and their propensity to store moisture for years on this forum. Where is the car being driven? Is it a cold environment? Hhow far is it driven each day and then parked to start condensing moisture? Even if its not cold, these thing will pump steam longer than most vehicles out there.

You've checked the usual suspects (mixing of coolant and oil does not need to be present if coolant is only entering the combustion chamber) and without evidence of an overheat, the most I would do at this point is find and fix the external leak, then if the coolant loss persists, find a good shop for a leakdown test.

The suggestion to pull the plugs is a good one, but the amount being lost may not be visible on a plug. Please post the results.

Good luck and keep us informed,

Dave

[whiskychaser]

Can we clarify how fast she is going on the freeway when she sees steam? Unless the engine is about to let go I dont think you would see it at speed. The drips when the car is parked would have me looking for an external leak.

[bubba966]

She's probably doing 60-70 on the freeway. I'm the one that drives my E34 faster than she does.

I know it wasn't exactly scientific, but when I pulled the expansion tank cap off there didn't seem to be any added pressure from it being overpressurized due to a blown gasket or head crack. Seemed to be pressurized just as my M-Sport would be. I know an M60 is different than an M50TU, but the cooling system pressures should be no different at all. And I've taken my rad cap off enough when it's hot to know what it should be like.

We are both well aware of the extreme mass of an E34 exhaust system is. I had to drop it to put a new O2 sensor in 2 years ago. So we both are aware of the fact that it takes a good deal of running to get it warmed up enough to get all of the condensate out of the system. But she feels it's been brought up to temp long enough and is still smoking.

And the temps as of late have been in the 30's-40's here around Seattle. And last week we actually had snow for most of the week.

I'm of the opinion that it's just an external leak as the damn thing hasn't shown any symptoms of a bad gasket or cracked head. Not that I've dealt with either situation. But the classic telltale signs of such a problem aren't showing up.

Will have to pull the plugs and get a look at them and the pistons (well, at least as much of them as I can see through the plug hole). Couldn't do it on my quickie check as the car was still warm.

At least a guy local to us has a '94 M50TU out of an E36 that had 125k on it and was run with synthetic. He's asking a reasonable price, and I'd bet it's cheaper than buying a just a head from one of the BMW yards.

[bubba966]

So, this morning I was able to check it out while it was cold.

No signs of coolant on the oil cap.
No signs of coolant on the dipstick.
No signs of oil in the coolant.

Plugs all looked normal.
Tops of pistons looked as they should.

It's still never got past the 12:00 mark on the temp gauge.

Seems to me there's a cooling system leak that's explaining the coolant loss as it's not showing any signs of burning coolant.

And the white smoke on the freeway I'm chalking up to the aerodynamics of the touring. I followed an E34 sedan down the freeway for a bit a few days ago. Quite clearly had white smoke from condensation rolling out of the tailpipe. But the aero of a sedan doesn't let the smoke come up high enough for you to see it while you're driving. The aero of a touring would allow the smoke to come up high enough so that you can see it out the back window.


Anyways, I told her I see no reason why to continue to assume that the HG is blown. And that she should continue to keep an eye on the temp gauge. And told her that should something nasty happen there's a 120k mile M50TU for sale locally that was taken good care of over it's lifetime in an E36 that's available for $600. So worst case scenario is $600 for another engine and a bit more to slap it in.

If anyone has anything else to say about this manner do chime in. Seems to me the mechanic that said she needed a $1,500 HG job just saw coolant loss and white smoke and said she needed a new HG thinking she'd just go along and have him do it.

[whiskychaser]

I'd still like to know where the inch of coolant is going every day :)