Re: Mercruiser Alpha 350 Mag - Oil dump
Don't necessarily assume engine is an anchor, never know once start it up.
the oil isn't coming from your exhaust manifold, either water leaking too or more likely it's something behind / above the drain on the manifold and is just running off the lowest point.
Great suggestions from smart, experienced people above.
Some things i would think about / consider whil trying to pin it down...
did your oil pressure alarm go of and did you still have oil pressure on the gauge?
do you have an external oil filter / oil cooler set-up? if one of those lines broke would empty things quick
A completely dislocated valve cover gasket can leak amazingly fast, as can the rear of the oil pan gasket or a rear main seal. The valve covers are high enough that the oil may just run down the back of the manifold.
if it wasn't leaking on the top, it is also possible that you may not have noticed and it may have taken a little longer than you might think at first glance (I do this kind of thing...).
rrusted through timing chain cover or oil pan can empty an engine quick as mentioned above,
another is if it's an older engine and has some blowby, if the crankcase vent(s) get plugged somehow, the buildup in crankcase pressure, especially under heavy throttle, will push oil out somewhere - wherever it can get out first, including places like the dipstick tube, etc... assuming your dipstick tube is on the startboar side, and opposite the side of the leak, that's not a likely candidate but excess crankcase pressure can make leaks show up everywhere / anywhere.
Pressure sending unit / switches can be the source of a major leak. If you've got an electric fuel pump, the cut-out / safety switch is can be mounted just above the oil filter and when they crack can leak a lot in a hurry. The pressure sending unit is more often in the rear and middle, but I suppose leak could run down something and look like it's coming off the exhaust manifold.
As you mentioned, oil filter is an obvious place to look as well.
after you check for the huge things, fill it back up with oil, start it on muffs and see if you can visibly see where it's leaking... if not, then clean it up with soap and water and try again. I've never tried this, but read recently that if you do a good job cleaning it up and then still can't see where the leak originates, you can (gently of course) applying a few "puffs" of bably powder to the suspected locations. The baby powder will stick to any oil and show you the trail its following (prudence would dictate not getting crazy with this... and not getting it into everything.. I've got a drip on my engine now and was going to try this next time I get a chance.
Hope you find it and will cross fingers that you're engine is OK...
Did you refill your engine with oil & try to re-start it? All you can do is clean it up & refill oil & try to recreate the event, and look hard......And observe it at idle first.....I guess you didn't keep an eye on the oil pressure gauge.....I would look for obvious leaks, like an extra gasket on the oil filter, oil pan leak, timing chain cover, stuff like that first...I do not see any relationship between changing your impeller and thermostat as the cause....You're just gonna have to get down there & look & that might take a little disassembly of the back seats and stuff for a good look......And what is your oil pressure now that you have re-filled the oil & re-started the engine?.....JK