Infamous Mercruiser 470 motor??HELP?

[frustratedboater]

I need some help with a problem that I am having with my 3.7 Mercruiser 40, 224 CID, 180 Hp motor:
I had lent my boat to a friend for his vacation and received a phone call about 9:30 pm: "R.... , The motor lost oil pressure so I shut it off, there is oil all over the motor, and its getting dark, what should I do"? (Needless to say, he is still my friend-

History: This motor had been sitting for 10 years before I threw it in my Four Winns 19' bow rider and only has 40 hours on it. I had changed all the fluids and stuff before running it.

I filled the motor with oil, took it out and ran it basically to see if or where the leak is coming from. There was no major leak or dripping from the front or rear of the engine, so I rulled out the main bearings. When it came to temperature (150-160), I did notice that there was bellowing steam from the valve cover vent tube area and looked to be a light greenish/milkycolor. Brought it in and killed the motor. Checked the oil color and it had a crystal clear amber appearance to it. I broke the motor down and pulled the head off to check the gasket and really didn't see any obvious rips or tears to the gasket and no real obvious cracks to the head.

Had the head pressure checked and got the thumbs up on that. I had it surfaced while I was in it that far. ..?..?...? This thing has me! I would appreciate any professional advice, or suggestions on where to check on this steaming/oil thing. Thanks so much for your help.

 

[Don S]

Re: Infamous Mercruiser 470 motor??HELP?

Sounds like blow by past the rings. Might try doing a leakdown test and see how bad the rings are.
I'm assuming when you said the oil was clear and amber, that it looked like new oil.

 

[frustratedboater]

Re: Infamous Mercruiser 470 motor??HELP?

Thanks for the reply. Yes, the oil looked like new. I have inspected the cylinders and noticed some pitting in #2, and the #3 cyl has a section that looks like a shallow wavy area like wearing of the cylinder. If I run my fingers over it, kind of feels like a smooth depression area. That doesn't explain the oil coming through the valve cover though.?.? Also my plugs were buring clean and had no smoky exhaust.

Q-What exactly is a leakdown test? Is it something that I could perform with basic tools? Thanks for your comments,
RF

 

[Don S]

Re: Infamous Mercruiser 470 motor??HELP?

I have inspected the cylinders and noticed some pitting in #2, and the #3 cyl has a section that looks like a shallow wavy area like wearing of the cylinder. If I run my fingers over it, kind of feels like a smooth depression area.

Sounds to me like the engine had water in the cylinders, they got all rusty, someone freed up the engine with all kinds of penetrating oil, then sold it and stated it runs fine.

Google "Leak down Test" and you will find more info than you can use.

 

[frustratedboater]

Re: Infamous Mercruiser 470 motor??HELP?

Thanks for the info on the leak down test-- it is not a bad idea at this point. I will try it when the head is installed. The previous owner had this boat sitting in storage (10yrs) and was paying $60 a month and the wife needed it out! So, I needed and engine and he needed to get rid of it, so pretty good deal for both.

At this point just trying to isolate the problem. Some other past threads on this site suggested that the exhaust manifold could be one of the culprits as well as the riser getting plugged with rust. Both of these seem to be in really good condition with clear passageways. Each of these could contribute crankcase pressure and spitting the oil out, but somehow it is mixed with antifreeze, which explains the bellowy steampot condition and milky color.

I am not really sure, but does this sound like any possibility to you? Sorry to be a nag, but just trying to rule out every possibility at this point. Thanks again,

RF