Oil in the coolant resevoir

[Rickman]

I've got a 91 K75s, runs great, plenty of power but I've been noticing oil on top of the coolant in the reservoir tank under the seat. Common sense tells me head gasket, but with an old Goldwing I've got it was a bad O-ring on the water pump. I'm checking to see if anyone has any suggestions on where to start with this before I start pulling the head?

[roninvt]

Hi Rickman,  is the water pump weep hole clear....any weepage??

[Grim]

Water pump and oil pump are in the same housing.

The question is how much oil.  A little film of oil I'd think maybe it was just some residue wasn't cleaned out during a water pump rebuild. Pull the radiator cap see what it looks like.

[Rickman]

 The radiator was damaged and unknown to me when I bought the bike a few months ago, when it started to leak I bought another one and installed it. When draining the coolant I noticed a brown oily substance and wrote it off as bars leak. It didn't look like oil, it was brown. Upon reassembly I put in new coolant, topped of the reservoir and been riding it without problem. Preparing for a ride last night I checked all fluids and noticed the reservoir tank was low, when I went to top it off I saw the brown liquid on top, about two inches worth.

[wmax351]

2 Inches worth? That's a lot. You should investigate it further. Did you happen to notice the fluid color prior to this? Someone may have put one of the special radiator fluids in (like the G12 or G11 Volkswagen group coolant, or Dexron for GM) and added the green stuff will turn those into brown, gelatinous muck.


I was concerned with just a tiny film on mine, which is likely just assembly oil that was in the coolant passages from my rebuild.

[Scott_]

Sounds like you need to flush it real good now. It's possible that it could have been just gunk from the replacement radiator, but you won't know now till you flush and refill, and test it.

Don't forget, DISTILLED water, not tap water for final fill up. You can use any standard auto anti-freeze coolant so long as it's rated for aluminum engine parts(and most are now a days). Just don't do the dex-cool orange crapola......

[johnny]

the question that needs to be answered is...

which has the greater ability to transfer heat... water + coolant... water + coolant + oil...

j o

[Rickman]

Well, I flushed it today, but I'm leery of adding new coolant. My bike does not use much oil at all. I topped it off the night before, it was down at about the halfway point of the window. After a 220 mile ride yesterday, and while flushing the system today, I looked at the oil window and its down about a third. This tells me I'm losing oil, albeit to my cooling system. The question now is where is it leaking into the cooling system? The bike sat for a long time before I bought it, I'll have to check my service manual and see if there's an O-ring or seal on the water pump that may have dried out and is now allowing oil to seep into the water. there are no signs of any water in the oil. I've been doing this for around thirty plus years, its my first BMW and I've never owned anything this new. My hope here is that someone can help cut down the troubleshooting time. Thanks for all your input thus far.

[Scott_]

K-bike engines can burn/use oil. up to 1qt per 1000 miles is within spec from BMW.
The oil can also "hide" in the motor. You can fill to the 3/4 mark, ride for a day or two and check it at 1/2 or less, then the next time you check it the level can be back up above 1/2...... I've seen it happen on both of my bikes.

[TimTyler]

...up to 1qt per 1000 miles is within spec from BMW.

That spec has got to be for the early bikes that seeped oil into the cylinders while on the side stand.  :yow

[Scott_]

...up to 1qt per 1000 miles is within spec from BMW.

That spec has got to be for the early bikes that seeped oil into the cylinders while on the side stand.  :yow

Speaking from my limited experience, others may say otherwise.
I've had to add oil to both of my bikes when on the road. Sometimes I can use a full qt, other times not.....YMMV
Even the newer 1100 engines with the newer rings and such will still seep some oil past the rings on the side stand.
Then there is the cc ventilation that can draw oil vapor and burn it. Doesn't seem like it's possible but the plumbing is there for it to happen. Vac lines from the block to the intake throttle bodies, so it's possible. BMW's "oil separator" design in the 1100 didn't last long(hold up). Maybe that was their intended design attempt to reduce oil consumption.

[TimTyler]

I guess I've got a lucky engine then. My oil level never drops noticeably between oil changes every 3 to 5k miles.

[Grim]

My 1100 has 48k. It's used maybe a pint in 2,000 miles.

Now there is some precedence for a false level. I've read about it and my bike has done it. Have no idea how it happens but one day I look and it's showing half way on the sight glass.  Next day it shows full. Parked in the same spot in the garage.  :dunno2:

[Motorhobo]

None of my 94 or 95 K75s over the years have lost any noticable amount of oil between oil changes.

Van