Raylar

To clarify: 496 Mercruisers and such do not have any water in the intake manifold or crossing over in it, so leaking intake gaskets will not get coolant in the crankcase. As to the oil cooler on the merc 496, it is cooled with raw water, so if it is cracked it can only put raw water in the crankcase not coolant from the closed cooling system. I have heard of some 496's with cracked blocks and heads with coolant entering the crankcase from freezing temps, but I would suspect that only would happen if the coolant (dex-cool) is below a 50% concentration. A leaking head gasket or cracked cylinder head on this engine leaking between a coolant passage and the lifter valley or oil drainback holes can put coolant in the crankcase.

Best Regards,
Ray@Raylar

HOBoater

I'm in a Ohio and we had a extremely cold winter. The engine was winterized with air pump releasing water. Closed system had factory antifreeze. There is no water in the cylinders and the compression is 160 to 165 for all cylinders. Where is the oil cooler located and how can I test it? Thanks.

HOBoater

If I dump water in the closed system it immediately drains into the crankcase. The boat is kept in a garage year around. I would like to try to trace the water without tearing it down.

tms1155

if it goes directly into crankcase its a cracked block or head. dont even bother with the oil cooler.Pull off intake and check in lifter valley.

Rage

Sea water flows through the oil cooler so no antifreeze. Antifreeze only flows through the block , heads, coolant pump, coolant crossover tube, heat exchanger and connective hoses.

HOBoater

Thanks for all the replies. I'll start tearing it down.

03 SONIC

I sold my brother my 2003 sonic with a 496 HO last month. He went to take it out today and get it ready for the summer and it did the same f@#$ing thing. It looks like a nice boating season so far. This is the second 496 that i have owned that has taken a s#$t. I bought a 2001 Formula 382 last year and the motors only had 32 hours when one let go. F$^k a 496 it is a bunch of overpriced junk! Both motors had under 100 hours and filled the crank case full of water. At least the sonic was not running when it happend.

Raylar

Don't bash the 496 engine! Improper winteriztion will do in any marine engine. Get the Merc manual and follow the winterization instructions exactly and completely and you should not have any block or head cracking problems. Do it wrong or have somebody else do it wrong and you will have a disaster in spring just like anyother marine engine!

We have also heard of some shops using 50/50 water and Dex-Cool mix when refilling 496's that will be in winter freezes. THIS IS WRONG, THEY MUST BE FILLED WITH 100% DEX-COOL, every 496 owner-log this in your memory chip and make sure your servicer knows this also!!

Best Regards,
Ray @ Raylar

jswfl09

I got 800+ hours on our 496 in less than 4 years and it is still running smooth and consumes no oil (at least not in 50-75 hr oil change intervals). I think that is a true testament to the 496. On the other hand, I boat in SWFL so winterization does not exist.

HOBoater

I have the intake off and the water is leaking from the head gasket on the right bank about half way back. I'm in the process of removing the head. I want to make sure it isn't cracked. What is the best place to purchase gaskets (head, intake, exhaust, and valve cover)? Are there better aftermarket gaskets?