With winter approaching I'm looking to compile a list of the common items that fail on these engines.

I'll spend the winter going over my engines because summer in Florida is hateful when you have to get down in the bilge and deal with anything.

The impellers, belts and hoses will get replaced.

I was told by the previous owner that the IAC needs regular attention.

Failures? None if you take care of them.

Common problem/maintenance areas perhaps? IAC, Sensors, Coil Packs. Water Pump housings.

Use them and maintain them and you're good to go.

If you have cool fuel 3 paint inside can peel off and cause havoc

Which Sensors are problematic?

StitchKing,

Running stock, you shouldn't have any real issues, other than what is stated. Keep an eye on the IAC. If the engine starts anything erratic, put a Rinda TechMate on it and make sure it's not the IAC, as it can fail, and can take out the ECM when it does.

Just know that, by 2004, Merc would have gone through all the forged parts they may have had, and the crank and rods are cast. Even in the HOs. It's not your grandpa's cast steel, but they are cast all the same. And, regardless of vintage, the 496s were all built with those damned hypereutectic cast pistons that won't put up with much in the way of detonation. I wouldn't put any power adders on it without correcting these issues.

Thanks. Brad.

If not mentioned, replace the crankshaft sensor, and I would replace the IAC valve, if everything is working properly I would perform regular maintenance and perform repairs as needed

I have a 2004 myself. I'd change out the IAC valve with OEM if you haven't in the past couple years. Also, pull the end caps off the heat exchanger (no coolant will come out) and replace the gaskets if they look to be delaminating or disfiguring. It's common they deform. (there's a little oring sealing the bolt on each end also, don't forget those!

My 2004 had the gen 2 cool fuel system so it didn't have any of the paint flaking issues that plagued the gen 3 systems.

Also, pull the inlet hose (towards the rear) on the oil cooler and look for debris caught in the tubes. The oil cooler is mounted down low on the port side towards the rear.

The pressure sensor for the seawater circuit and the oil pressure are the same part number on an '04, so I keep a spare with me in case one fails.

Another good thing to check would be to unbolt the water inlet fitting from the inner transom assembly and look to make sure the water hose isn't getting restricted. Look up bravoitis for photos of what happens.

Regarding the IAC taking out the ECM IIRC there were some threads about adding a fuse to the IAC to prevent this. I believe it was as simple as just putting a 1 (maybe less or more) amp fuse inline with the IAC power. Can anyone expand on this or was it limited to a certain package or all IAC equipment engines?

I don't think that was on the 496. I think it was the 600sci??

What can take out the iac on these engines is a small filter in the tb that gets clogged with belt dust. Make sure you change the filter yearly. It can get sucked into the iac.