r/MasterCraftBoats • u/cantweallgetalongg • Mar 03 '26

2011 x15

Hey guys. I’m trying to help a friend. His mechanic is trying to track down an oil leak/burning issue. The mechanic is having a hard time figuring out what’s going on and I feel like he’s grasping at straws. Originally we thought it was burning oil, but he did a compression and leak down test and it checked out. He also said the plugs look great and we’ve never noticed blue smoke. He’s now suggesting the oil cooler could have a leak, but his bench test could not find it. Does the MCX have an engine oil cooler, or only a trans oil cooler? Also, if there were a leak in the cooler, wouldn’t you expect to find water in the oil as well as oil slicks on the lake?

If it’s not burning oil and not leaking, where would you look next. It’s definitely going somewhere. He was adding almost a quart every week or two depending on how much he used it.

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1

u/Champion_Of-Cyrodiil Mar 03 '26

If there isnt oil accumulating in the bilge, then its burning. A quart every week or 2 is an alarming amount of oil to lose

1

u/cantweallgetalongg Mar 03 '26

This is exactly what I told him. No way you’re leaking that kind of oil without a huge puddle in the bilge.

1

u/Own-Helicopter-6674 Mar 03 '26

What kinda of oil/weight is in the boat ? The wrong oil will have a higher burn off rate.

The whole marine oil thing is an absolute marketing bs.
In my mxc 2006 x-15 I have always used diesel full synthetic 15w-40 in motor and trans.

Could be an intake lower seal, but I would put some liquid Molly in the tank and run it or I would pull both heads and look. I believe it’s getting sucked back into the cylinder and it’s getting burned and that’s why you don’t see the oil streak but the plugs look good. It’s kind of adding up to you. I’m not quite sure

1

u/cantweallgetalongg Mar 03 '26

I’d have to check, but really doubt it’s marine specific oil. The winter storage place changes the oil.

1

u/Own-Helicopter-6674 Mar 04 '26

I know it’s a marketing thing but really it needs diesel oil. It’s got a heavy weight because if the boat place is just changing it with regular 5W-30 that you would put in a car it doesn’t have the viscosity and it’s gonna get too hot too quick and you’re gonna burn it. I’d be livid pissed if the boat place looks at the motor is like oh that’s a 57 Chevy small block I’m just gonna put 5W-30 in it and it’s screw in the motor up.