Having a problem with milky foam coming out of the breather. The oil on the dipstick looks fine. Found this problem last Sat, changed the oil, and cleaned the breathers and the hose attached, took the boat out and the milk is still back. Engine runs great, it does not skip, run or idle rough, top speed is still the same. Water temp around 160 and goes to the ocasional 180. Oil pressure is 40 and above off idle, 25 - 30 on idle. This is a stock 502 with mercruiser exhaust and risers to thru hull exhaust. Took the risers off to see if there is any evidence of reversion, riser looks fine in the center gray exhaust, though rusty in the other water jackets. The gaskets did look rusted and beat. The water I was running in was pretty cold, I would say in the 50s. Could this also be a case of condensation? Any ideas would be much appreciated.

I have had this same problem on a small block and it was in fact a case of condensation. I put in a hotter thermostat and the problem was solved.

I agree with Katdrvr, depending on where you boat and the Oil Temp. Do you have an Oil Temp Guage ? You may want a collector on this as well to mearsure the amount.

Had somewhat of the same but mine was from the rebuild, shop did not put thread sealer on the six bolts on the intake manifold that are on the water ports and go through to the inside of block. You said your water temp. is 160 how much higher should it be guys?

It is more of an Oil Temp issue than the Water Temp. The real issue is does the oil get hot enough to "Burn off" the condensation ? If it does not you may have too large of an Oil Cooler or need an Oil thermostat.

Seems if it ends up in the breather it's hot enough to have been vaporize and not collect in the pan?Yes oil temp must get over boiling point of water. I also wanted to know how hot can we go as I am putting a closed cooling system this time, can we go up to 180* on marine motors.

Thanks for the responses.. I do not have a oil temp gauge, but it would be a good idea to. I pulled a couple of plugs and they seem to be burning fine. Hopefully it is the condensation or the riser gaskets and not block or head issues.

If you have a remote oil filter it is easy to install and woudl help at least figure out if this is the issue.

m10jb,
Floridianson had a good suggestion, I would pull (one at a time) the 4 intake bolts at each end of the intake manifold and put a little thread sealer (I like Permatex #2) on the bolt threads and reinstall. I would then go back over all of the bolts on the intake manifold in the proper torque sequence and re-tighten.
This is an easy place to start.

What year is the motor? Has it ever been apart? I had milk coming out of my breather tube late last season on my 95 502MPI. Shortly there after where was a little water in the oil. I decided to replace the manifolds(they were original) and while i had it apart I noticed the backflow preventers(flappers) in the Y pipe to my outdrive were broken off and gone. I put new flappers in and new manifolds(IMCO) on and the problem was fixed, im still not sure if it was the manifolds or the flapper being broken that caused the problem. Either way it needed the manifolds and there was a noticable performance gain!