It doesn't look good......
 

I've come to you for help again. I have a 87 s4with a 5 speed and 84000 miles on the clock. About 2 weeks ago the low coolant level warning light went on as the car was parked in my driveway. I added about a pint of antifreeze, and went about my way. I didn't give it too much thought, as I have a slight leak by the water bridge. Two weeks later, and I back the car out of the garage and see a ugly puddle of brown sludge coming from the coolant overflow tank. It's now chock full of this oil and antifreeze mix. The car starts right up and runs as good as it ever does. I do run the car hard, when I do use it on the weekends, but never is it beaten on. What happened? And where do I go from here? what am I missing? There was absolutely no warning of something going wrong. And now I'm sweating the possible outcome. What do you think?

Lots of potential problem areas with some being worse than others.

Pull the spark plugs and look for any hint of coolant washing things down.

Drain the engine oil and see what you find there.

If there is no hint of coolant on the plugs or in the oil best bet is the radiator is allowing oil from the oil cooler into the water.

I am sure others with more experience will have other ideas as well.

Went to the dipstick immediately, oil was a little low, but no water mixing in it. Haven't pulled the plugs yet. Don't mind my ignorance, but it's got an oil cooler built into the radiator?

Sorry, should have read you post closer, the cooler I am referring to is for the automatic and I see that you have a standard.

I should let someone who knows this issue better chime in - sorry.

Yes i think 85 up has an integral oil cooler, there should be hard flare fittings in the top and bottom of the left end tank, this perspective would be looking at the engine from the flywheel side. Not sure on the year they were included on, don't quote me on that.

Well you got past one hurdle if there is no water in the oil. I will be watching this thread and hoping for the best for you. Keep us updated.

Yes, there's a cooler built into the driver's side end of the radiator (LHD driver's side), up to 1989 (1990+ got an external one).

Oil pressure runs higher than coolant pressure (up to 8 bar IIRC before the pressure relief bypass opens), so you get oil coming through into the coolant.

You need to pull the radiator. Being a 5-speed, your radiator should only have a single cooler in the driver's side end.

Check for fittings on the passenger side end too - many replacement 928 radiators fitted just use the auto version (coolers in both ends), in which case any shop that works on Behr will be able to remove the leaky cooler and move the other (unused on a 5-speed) cooler to that end - you'll be up for the cost of 2 plastic end-caps and the labor. If you're game, you can do this repair yourself (end-caps available from this forum's sponsors - from memory around $100 per end)

If yours only has the threaded fittings on the driver's end, then rather than screwing around with getting the internal cooler repaired, I'd just get a new Behr radiator, as they're cheaper than the aftermarket ones, and proven to last 20 years.

if your absolutely sure the oil in the pan is clean then a blown cooler in the radiator.

NOTE remove the cooler lines from the radiator and if you find any coolant then then radiator cooler is damaged.
leave the coolant in the radiator and pressure test the system with the oil cooler lines removed
once this test is done then drain the coolant and add some tide and fresh water and flush it ,remove the thermostat.
NOTE dont run the engine as you will quickly pump out any remaining oil with the lines off
figure that you should replace all of the coolant hoses as any hoses exposed to oil will split or slide off their fittings as the rubber will get soft, that include a new heater control valve and short hose and the heater hoses.

NOTE you can also try capping one of the cooler line fittings on the radiator then putting 50 PSI into the other end,work your way up to 100 PSI
then with the coolant cap off see if you find bubbles in the bottle

Correct most likely a leak in the heat exchanger which leaks 100 psi oil into 14 psi coolant. An $800 problem instead of one several times that.

Drain the oil and check for water. Oil floats on top of water in the sump. Dipstick only gets into the top layer in the sump.

A leak between the oil system and the cooling system moves oil into the coolant with engine running, coolant into the oil as the engine cools off. Generally. Grab a sample of the slime in the reservoir and see if there is actually oil in there before you make a rash decision. The drain from the reservoir is just long enough to rinse slime from the engine to the ground. Oh.... and fix the water bridge leak before it gets any worse.

Dr Bob, you are a gem. We are so lucky to have you here. You are always so willing to help, so patient and positive in your suggestions and I sincerly thank you for it. I wish you were on the east cost, I would love to met you some day.

Water in the engine is bad. Oil in the cooling system not so bad. I had this exact issue occur with my 89. It's very, very likely your radiator/oil cooler. I'd bet big money on it if I had any to bet.. ;)

A very easy test for the radiator is to take a bicycle inner tube, (llarge mountain bike type) cut the tube through opposite of the valve. Stretch the opening of one end over the inlet of the rad, and the other end over the outlet of the rad. Clamp the ends on the rad. Remove the oil lines from the rad. Inflate the inner tube slightly. The inner tube will deflate slowly if the rad is bad.... Milkshake is scary, but in this instance you are probably fine with a new rad.


When I installed a new radiator, I used automatic dish washing detergent in the cooling system to remove all of the oil. (two cycles). The liquid Cascade will not foam...

ran the car for a few minutes today, just long enough to turn it around in my garage. will get to jacking up the car and dropping the engine shield to drain the oil probably by the weekend. I will keep you all posted and I hope that your right, that its as simple as a bad rad. thank you all for your help and your advice. it looks like i'm gonna have to take this on myself, as the kids insurance premiums are soaking up the 928 repair funds! (thanks to n.y. state)

If it isn't the cooler on the passenger side of the radiator, it could be a leaky head gasket allowing oil from one of the galleys into the coolant passageway. Hope it's the radiator!

stuck here....
 

I managed to get lots of things drained, loosened, and ready for removal, but those fittings on the rad ARE A KILLER! its a 30 mm hose fitting screwing into a 27 mm which in turn screws into the rad. it will only loosen less than a flat, and stops. it will tighten back up again, but i gotta get this thing outta my car. any hints, tips or suggestions? i dont want to force it and break anything.