Merc 300 xs optimax 3.2 racing
 

anybody having issues with this motor , I have a friend with brand new in 2009 motor under 25 hours who keeps seizing pistons for the 4 th time . runs mercs best oil, 93 oct gas doesnt run the piss out it . no alarms go off , isnt overheating, not over reving on a 22 ft v bottom boat.
were all stumped . Need input from other owners .

I had a couple on my Cat and they didn't perform the way that I expected..Anyways, what size fuel line are you using..3/8...5/16...etc...This was the cause of one of mine..

he is using at least 3/8

Have all the seizures occured on one bank?

Over here in australia we had several do the same thing around the country. Mercury started looking into it and ended up stripping all 300xs motors that had left the USA before the realisation and had them re honed as the tolerances were too tight. I believe all the failures occured on the left bank!

I ordered my 300xs November 08 and never got my engine (even though it was in the country) till march 2009 due to this procedure taking place.
All i can think of is you have got an engine that was manufactured with this inherint problem.

By the way my engine has never faulted , however i had several niggling problems which i attribute to the procedure which took place. eg: recieved engine with pin hole leak in air hose from compressor to fuel rail which wouldnt allow engine to idle or run at any rpm properly. Took weeks to find the problem even with mercurys assistance. In the end i found it myself. Just one of many annoying side affects i attribute to it not being addressed in the factory by the team that build the engines.

Failure has happened mostly on left bank number 3 and 5 cylinder but I had one failure that included number 6. Gee I wonder if that is the problem????

My 2007 30/308 Skater came from the factory with T/300XS. After 3 weeks (30 hours), one motor melted piston 5, and ventilated the block with the connecting rod. The power head was on national backorder so I was down from May 27 to Sep 28.

Since then the only other engine failure was a burned up coil and ignition harness at 97 hours. Presently, I have 120 hours on one and 90 hours on the other, but for some reason the computer shows 120 & 118 hours?

The real problem has been the lower units. I am on replacements 5 and 6. I was cracking them like clockwork, and other owners have reported the same thing.

Both lower units gone as well..

I know merc had problems with coils I burned up 3 of them but they sent a new design worked great .

Call merc, maybe its a lemon. I loved mine, put over 130 hours on it without ONE breakdown and only routine oil changes.

Its our 4th one