BMW query for Motu or Sidecar Bob

[eliot-ness]

After my little radiator incident at the wekend I had the car towed in to the BMW agents for repair. Got a call from them yesterday. They've fitted a new radiator but when they run the motor the water gushes out of the filler cap after a few minutes. They reckon it's the head gasket at least, could be more serious. My first thought was the thermostat isn't opening, they hadn't checked that??? but didn't think that could cause it. I've seen it happen in older cars but haven't had much to do with them since the 80s so I'm not up to date with modern stuff. They are quoting up to 4 grand for repairs. Any ideas, (apart from scrapping it) Bob and Motu are the only ones I know of on the site who are in the trade so I addressed the question to them but advise from any other auto technician would be appreciated.

[Dooly]

Thats usually a symptom of air in the cooling system.

Reasons, cooling system needs to be bled properly after a radiator job, and that, on some cars can take ages, up to an hour or more, and then having to leave with engine off for the water to settle and air to come to the top.

Possibly thermostat issues too, quite common.

Of course a blown head gasket or cracked head will do it too.

A test for compression in the cooling system will show up a head gasket too.

I don't know how many times I've seen people have thought a head gasket has gone when its only been a radiator/thermostat/fan issue.

Don't give up just yet!

And yeah if its Beemer and the heads gone.............oh dear.......*cash register*
Mind you, I don't know what your radiator 'incident' entails.

Oh, and I'm an auto tech. (Mechanic in non PC terms.)

[Max Headroom]

Maybe none of my business, but for what it's worth I wouldn't be letting anyone touch the engine without seeing the results of a compression test at the least, or a leak-down test ideally.

I presume you have a K75 or K100. Either way, a replacement s/h engine would make more sense than spending that much coin rebuilding an engine that's been seriously overheated. If it was just a momentary overheat that popped the headgasket, that's different again, and quite viable to repair from a $$$ point of view.

(I'm not in the trade any more, but I was an engine reconditioner for many years and still fester with stuff at home.)

just my $0.02

[Mully]

Mate, it's his BMW cage that's the issue.

FWIW, a second hand engine might be te go anyway...... Depends on the value of the car, I guess.

[xwhatsit]

I presume you have a K75 or K100.

It's actually a car. Which a K75/K100 more or less is anyway, but the one he's talking about has four wheels

[Max Headroom]

It's actually a car. Which a K75/K100 more or less is anyway, but the one he's talking about has four wheels

Fair enough. Not mentioned in the original post.

Same rules apply. At least a compression test or ideally a leakdown test before letting anyone near it with a spanner. Otherwise you're in for an expensive guess. And a serious overheat does weird things to alloy bits - they're often less stable and continue to give problems. Rings can lose tension too, resulting in an oilburner.

How bad was the overheat?

[eliot-ness]

Fair enough. Not mentioned in the original post.

How bad was the overheat?

Guage just showing in the red and no warning message flashing. No smoke from crankcase when I removed the oil cap.

[Matt Bleck]

HDT boy works on BMW's in Auck's somewhere, send him a PM.

[Motu]

A thermostat replacement,or at least test is mandatory for an overheated engine....maybe they just don't want to add anymore to your bill and get it out of the shop.BMW's can be a bit of a pain to bleed - the expansion tank is part of the header tank and never quite seems to work as you'd expect.There is a small bleed screw that you can release for bleeding....but again,doesn't get it all out.They need to do a few more tests to confirm a headgasket than just tossing water out....and they may have done that and not filled you in on details you don't need to know.

But blown headgasket after overheating? Very,very likely.

[pete376403]

Or a blown headgasket/cracked head prior, which then over-pressurised the cooling system and forced the water out, leading to the overheating.
Besides the obvious "bubbles-in-the-cooling-system" isn't there a test that detects combustion products in the water? (ie adding some thing to the water which turns a different colour).
Any water in the engine oil? (milkshake on the dipstick, white sludge in the cam cover?)

[eliot-ness]

A thermostat replacement,or at least test is mandatory for an overheated engine....maybe they just don't want to add anymore to your bill and get it out of the shop.BMW's can be a bit of a pain to bleed - the expansion tank is part of the header tank and never quite seems to work as you'd expect.There is a small bleed screw that you can release for bleeding....but again,doesn't get it all out.They need to do a few more tests to confirm a headgasket than just tossing water out....and they may have done that and not filled you in on details you don't need to know.

But blown headgasket after overheating? Very,very likely.

Thanks all. I don't think they'd done any tests when the guy phoned. He jumped straight in the deep end and started to tell me all the things that could be wrong and they'd have to take the head off to find out. Could be that he was warning me about possible cost, which doesn't worry me, the wife pays that and she needs the car. What does worry me is that the possibility of a thermostat problem hadn't occurred to him. I prefer to start with the simple stuff and work from there.
No previous problem with the car, no water in oil, no misfires, just had full check up. Whatever went wrong happened when the radiator burst, the motor had been switched off for five minutes, and guage no longer in the red. Haven't heard from the guy today so I'll wait and see what he says. Whatever the cost it'll have to be fixed before she trades it in.

[tri boy]

Pressure test the cooling system.
Also test strips, or solution testers show up combustion fumes in cooling systems.
Feck paying for engine work unless it's totally necessary.
As a side note, all cooling systems smaller than say a truck system should be filled at about 1.5l a min, ie SLOWLY. Saves alot of mucking around trying to bleed trapped air. MHO

[Rollestonchick]

How is your hand, now eliot-ness?

[Pedrostt500]

I was taught many moons ago to preform a cylinder blow by test, it was a good but involved test for problems with the combustion chamber.

[Motu]

What does worry me is that the possibility of a thermostat problem hadn't occurred to him.

Bit of a worry from a BMW specialist.The thermostat is on the intake side of the pump on these,and that leads to more bleeding problems.They are easy to get at,and running without is an easy confirmation of headgasket or thermostat....also eliminates air locks in that area.Pressure testing for a while,and then cranking with the plugs out is an easy test if they can't confirm with engine running tests.You need at least 2 confirms to say headgasket.

$4,000? Is this a VANOS? Even so,they are not that special and shouldn't cost much more than a Jap car to do a head job on...parts are cheap too.