Hello everyone,

I would like to know why the oil in my 496 turns jet black only after a few hours of running the engine? Last season I changed the oil and filter three times, and after each oil change it did not take long for the oil to turn black...granted by the third oil change it was staying cleaner longer, but it would adventually turn black. This season I changed the oil twice...same result. Total time on the engine is 103hrs, and I ran the engine 30hrs this year and the previous year I ran the engine about 25 hours. The oil in my diesel truck is cleaner after five thousand miles....the lawn mower oil stays clean all season...??? When I drain the oil in the boat I use the bilge drain hose and I pump it out. I always warm the engine up so the oil flows out easier, and I let it drain for at least an hour to try to get all the oil out of the engine??
Any help on explaining this would be great!!!

What oil are you using? Have you had the oil tested?
Sometimes oil color after use has not much to do with oil quality, lubrication ability or true state of the oil.
Unless you test a base sample of the oil before its used and then a sample of the oil after its used you can't really determine whats been going on in the engine or with the oil itself.
Good topic here! Lets discuss some more and try to clear up some oil concerns here. We've got a lot of great oil experts right here on OSO and I am not really that much of an expert.

Regards,
Ray @ Raylar

we use mercury 25 40 blend along with merc filters. i have had some 496's with very dirty oil, that turned out to have i.a.c issues. these engines ran rich at idle and slightly off idle. they were also not maintained well as for fuel filters, i.a.c muffler's, and flame arrestor's. after a thorough service maintanance, the black oil issue seemed to go away. could be coincedence, but for this situation i dont think so.
good luck.

Normally black, dirty oil after it has been used is a good thing.
It means the detergent in the oil has kept the dirt in suspension so it can be drained out. If the oil comes out clean, that means all that dirt is deposited inside the engine.

If a rich mixture or IAC issue is causing this problem, there are other signs that should be evident. Rough idle, black transom, soot floating in the water, etc. Do you have any of these things happening?

The 496HO is a SmartCraft engine you can scan. If the IAC is bad it usually sounds an alarm and puts the engine in a reduced power mode. (Guardian).

I have seen the same problem in my buddys 27fever. He changes oil every 25hrs. Was using merc oil and then switch to RP20/50. Same results...black oil after a few running hours. It has been a concern to say the least. Getting a solid answer on the problem has been a concern as well. He sent out to samples two get tested and they results were normal...

the i.a.c issues i am refering to do not allways show up on the smart craft monitor nor the lap top. as stated typicaly the do show other signs. as for the dirty being o.k, i might think that on a newer engine with not so many hours that it is not a good thing. especially if the oil is changed and within say 5 hours or so its black.
another thing to check is the engine oil cooler. on many 496's i have serviced i have found restricted oil coolers, loaded with seaweed or eel grass and the like. this will also help in turning he oil black and will not show up on the smart craft monitor or the oil temp guage.

Monstaa is right I too have seen some issues like this on clients boats.. It would be a good measure to do a back flush & impeller.. Also what oil are you or your marina using? Most places do use good quality lubes, however there are some places that will use the cheapest junk they can.. Just a thought..

Also there is an oil analysis that you can do on your own.. It is not the same as a lab doing it, but it will give you an idea of the amount of oxidation, moisture, fuel & junk in the oil.. I think it is called engine check or something like that.. We use it at times in our shop & it works ok if you are only doing basic checks.

Jamie / Lakeside


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Just a thought, maybe the oil left in the oil cooler"still black" blends with new oil thus makeing it black.

Maybe getting some blow by somehow in the worst case????

I would guess high oil temps. What are they running?

BT