What *really* happens when oil and antifreeze mix?

[Jon]

I've always wanted to know what *really* happens when oil and A/F mix (assume at operating temperature of an engine). I've heard it forms a "sludge" or an acid. What really happens? If it does form something, will repeated short OCIs flush out whatever it is, assuming the leak is fixed?

I've got a water cooled motorcycle that developed an A/F leak and, although it was probably only run like that for a short while (certainly < 300 miles, and probably less than 100 miles), I'd like to know about what I can do best improve my chances for a "keeper".

 

[williar]

I don't know what chemically happens, if anything. But mix oil, water and air well enough, as in an engine, and it causes the oil to turn a creamy white. The foamed-up mix does not lubricate, flow, pump, or cool well.

If you have the coolant leak stopped, then I'd flush the engine a couple of times with a good crankcase cleaner (Rislone?) then with fresh oil. Best to drop the pan and clean things up, first, including the oil pickup screen.

 

[eljefino]

It turns into something resembling microwaved peanut butter.

Worst thing is it's still somewhat viscous at 230'F then when the car overheats-- bam! it stops flowing, cools down, and all but solidifies.

Depends on which system is compromised-- oil in the antifreeze system can be eventually rinsed out with fresh water and automatic dishwashing detergent. Gummed up oil may require one drop the pan and scoop out the sludge to clear off the pickup.

 

[Jon]

Can anything be done? The bike *may* have had a /small/ leak for a few months, but total mileage for the entire year is under 400 miles. Will any particular oil or additive (like AutoRX, I'm not going to do an engine "flush") dissolve the A/F? I'm more than willing to do very short and frequent oil changes if that would help. The engine itself is being torn down (at least down to the heads) and will be cleaned, I'll make sure that the oil pickup and pan are also cleaned as part of that operation.

 

[dwendt44]

Fix the leak; change the oil with a cheap 10w-40 car oil.
Run for 50 miles, change oil again with good stuff and sleep easy.