Coolant loss- 95 525, M50

[peterllo]

I first posted on this problem this past March. Loss of coolant, frequent top ups, most severe when really cold. Replaced the auxiliary tank orings, problem persisted. The issue was resolved by replacing the radiator which had been replaced twice before once at 79k, then at 122k. The March fix was done at 150k followed by the replacement of the auxiliary pump and hoses. I detected the leak at the the inner lower corner of the radiator where the aluminum clamps to the plastic expansion tank. There was white residue (dried coolant) on the surrounding area and I could see a tiny (pinprick) of wet in the corner. The mechanic said the leak was due to thermal contraction, when it was cold outside the the plastic and aluminum contracted at different rates allowing the leak, once the car warmed up no problem, the expansion of materials closed off the source.

[I]To the present,[/I] low coolant light comes on, the auxiliary tank down to the top of the sensor. Car now has 163k on it. Topped up and everything is fine. No drips on the ground, hose fittings, water pump, firewall or inside. Seems like my old friend the corner leak has returned, residue on the expansion tank, a damp corner. This seems very odd to reoccur twice, likely three times but I did not own the car the first two radiator replacements.

So the question is why? Is it pressure related? What should I check? I have seen posts about checking for an internal head gasket leat by checking the plugs, I thought I would do that. There is a very slight, but steady, seepage of oil on the pass. side of the block just above the motor mount.

Any ideas would be appreciated.

[azale]

Rest assured that the anitfreeze gnomes are probably not the cause of the missing fluid. There is a logical explanation.

Quick thought: has the expansion tank been replaced? I think it would be cheaper than a new radiator and it may be half the problem.

I'll give you some possibilities but I'm hoping the experts here will have better info:

1. It is leaking into the pistons: your exhaust should be white and fluffy. Everyone driving behind you should notice depending on the severity of the leak, and your sparkplugs should manifest the leak as well. They are quite easy to remove with the BMW tools in your trunk.

2. It is leaking into your oil: your oil is now bubbly and milky brown like a great big chocolate milkshake.

3. (I've never seen this happen) You are getting too much pressure into your water system and it is blowing by the exansion tank. It *might* be possible for oil or expanding gases to force their way into the water jacket and over pressurize your antifreeze system. It might leak past the exansion tank and onto the ground but you would be driving and wouldn't notice. [Your antifreeze would be bubbly or dirty??]

4. You have a random leak when your car is all heated up. It's leaking but you're driving so you never see it.

Make sure your oil, antifreeze, and plugs look good. Then, top it off and let it heat up or drive it around and watch for a leak (or for the gnomes).

[jv9999]

I also have a '95 M50 (197K) and it does the same thing. I never see any leaks, the radiator is fairly new, and the oil is clear. Anti-freeze is cheap so I just top it off once a month or so.

[peterllo]

Thanks. Yeah I pulled the plugs last night, cleaned them up they appeared to be normal, one had a bit of glazing on the ceramic.

The radiators when replaced were the complete kit and caboodle, only had to swap over the coolant temp sesnor.

No smoke except the normal warm stuff now that it is getting cooler her in the Mid-Atlantic.

Oil and coolant are not mixed.

Pressure would seem to be the issue, hence the repeated leak in a corner where the crimping is. But why the pressure?

[azale]

So the oil looks clean and so does the antifreeze?

Bruno's site mentions an antifreeze leak in the heater core but you'd smell the leak so that is probably not the problem.

How often do you have to top it off?

You could probably get a radiator pressure tester for a small credit deposit from a local parts place (autozone, murray's, or advance auto if you are in the U.S.). Once the engine is warm you can check your findings with Bentley's manual or with the other experts on the forum.

The best way to find it is still to let the car get warm and then look for a leak underneath.

btw- do you let your BMW warm up nice and slow or do you slam it into gear and merge into expressway traffic?

I remember having a radiator leak for one day on my van and then it never returned. Never did figure out what happened.

[chefdanny121]

I have been battling the same problem and I am very curious for the solution!!!

[Hallmark]

Both have radiators replaced in the last year, neither shows any signs of leaking from an area that leaves any residue. No smell from the heater, although the leak is worse when you run the heater.

I'm thinking of running some leak stop through them just to see if that helps. As it is we have to top off the tank every 4 or 5 days.

[uscharalph]

So the oil looks clean and so does the antifreeze?

Bruno's site mentions an antifreeze leak in the heater core but you'd smell the leak so that is probably not the problem.

How often do you have to top it off?

You could probably get a radiator pressure tester for a small credit deposit from a local parts place (autozone, murray's, or advance auto if you are in the U.S.). Once the engine is warm you can check your findings with Bentley's manual or with the other experts on the forum.

The best way to find it is still to let the car get warm and then look for a leak underneath.

btw- do you let your BMW warm up nice and slow or do you slam it into gear and merge into expressway traffic?

I remember having a radiator leak for one day on my van and then it never returned. Never did figure out what happened.

One way of determining if the leak is in your heater core is if, when you turn the heater on, you get steam or for in you windshield on the driver's side.

[peterllo]

Nope, no steam, no drips, no smell, just the coolant loss through the radiator. I guess the next step it to pressure check the cooling system. Am I right in guessing that a high reading would indicate a possible headgasket? The loss is very slight, it took five months for me to notice.

This past spring right after the radiator replacemeent I replaced the auxiliary water pump, it blew. Talk about steam!

[azale]

I don't know what pressure is ideal. Incidentally, I just noticed that my antifreeze is low (after I took my e34 on its first 1500 mile weekend). I may be experiencing a similar problem.

I think what we really need is some of the experts to chime in. Where is a hero when you need one?