I took the lid off my drive lube bottle and it overflowed about a 1/4 of a quart of oil and bubbled alot...

What in the hell would cause that?

Was the oil "milky"? Had you just serviced the drive? If so, how was it filled and what is it filled with? Is this the first time it's happened, spacers, hot when checked, single or twin, etc.?

I just had the oil changed to AMSOIL. This is a twin application and I ran it all weekend somewhat hard here and there. It is not milky. But my shifter is not working well now either. Weather the problems are related I dont know.

I'm a former Mercury employee and have always recommended the Mercury Hi-Perf gear lube. That being said I know there are many good brands of oil out there and I doubt that's the problem. I wonder exactly how the oil was refilled? I assumed there is no burned smell to the oil? Did you pull the vent plug yet? It should run out clean and normal smelling. I'm just wondering if it was filled from the bottom plug up. Is this the first time for the problem?

Before you do anything rash try a new drive oil resevoir cap they have a valve that can go bad and a o ring that can get lost.

New cap should fix it...mine did the same thing this year, I switched the cap from one engine to the other and guess what...the overflow switched too. I just ordered two new caps (I'll keep one as a spare from now on)

Good call relaxalot, it did not occur to me. The standard cap should maintain up to around 26psi. I never fill more than it takes to keep the sensor from going off. The fill line is a little high.

Ive seen the merc oil not foam as bad as the Amsoil,but my drives foam bad anyway.I run the Amsoil,