oil blow by on mercruiser 470

[tobra100]

motor runs great, but at higher RPM's, it shoots raw oil out of air cleaner hose

 

[achris]

Re: oil blow by on mercruiser 470

By 'air cleaner hose' I will assume you are referring to the crankcase vent hose that runs from the top of the rocker cover to the flame arrester on the top of the carb. The only way oil could be ejected from this hose is if 1) the crankcase is seriously overfilled with oil, or 2) you have an enormous amount of blow-by passed the piston rings.

Chris...............

 

[tobra100]

Re: oil blow by on mercruiser 470

yea, I suspect the worst, but the motor runs so good. Is there possibly a quick fix? maybe an in line pcv valve or something?

 

[bhammer]

Re: oil blow by on mercruiser 470

How long have you had this issue? Did it just show up? Any type of background will be helpful. You need to do a compression check / leak down on the engine. I'd imagine you have some piston rings not doing their job or a head gasket. Have you had an overheat? A pcv valve won't fix the problem, only hide it.

 

[tobra100]

Re: oil blow by on mercruiser 470

I just got the boat running. It sat in storage for about 6 years. I ran it for about 6 hours while fishing and just noticed a little oil. but now, after running it for about 15 min at 2800 RPM, the top of the motor was saturated.

 

[cheburashka]

Re: oil blow by on mercruiser 470

One thing that will cause the same problem even in an engine with good compression is oil that's diluted with fuel. Have you checked the oil level? Have you verified that the crankcase is full of oil and not oil/water or oil/fuel?

 

[hard-3]

Re: oil blow by on mercruiser 470

do compression check and cylinder leakdown test if ok bad valve guide seals possibly leaking compression past valve guides into top end . How much oil is blowing out. A little oil looks like a lot when it is airosolized try catching in a can - take a soup can and put hose down in it with a top of steel wool to keep it from blowing oil out. If it had umbrella type valve guide seals they are bad about dry rotting and splitting. it's not a bad job to replace them ,just get an adapter that screws into sparkplug hole and connect air hose to it to keep valve closed . get a valve spring compressor to remove spring and put on new seals -on each valve reassemble and adjust valves. couple of hours labor .

 

[bruceb58]

Re: oil blow by on mercruiser 470

I have seen this on engines that have been laid up for awhile. One or more cylinders will get rusty dpending on where they are in the stroke and which valves are open. Then the rings travel through all this rust and it ruins them, not even mentioning what the condition of the cylinder walls may look like.

I really doubt they are valve seals. Valve seals do not have anything to do with any sort of compression as the previous poster said. Valve seals are there mainly to keep oil from leaking out rather than keeping gasses in. Valve guides do a pretty good job of that themselves.

 

[bhammer]

Re: oil blow by on mercruiser 470

I have seen this on engines that have been laid up for awhile. One or more cylinders will get rusty dpending on where they are in the stroke and which valves are open. Then the rings travel through all this rust and it ruins them, not even mentioning what the condition of the cylinder walls may look like.

Agreed!!! When the boat wa laid up, do you know if it was properlly preserved and when you brought it back to life, did you just crank it up or did you oil the cylinders and prime the oil pump?

What is your oil level? As mentioned, water or fuel in your oil can cause this issue. If it is normal, then you need to move on the the compressiona nd leak down.

 

[tobra100]

Re: oil blow by on mercruiser 470

Thr boat was not stored properly. bilge full of water. the starter had to be replaced. I inheirated the boat from my brother in law. estate settlement. I got about 2000.00 invested totally. its an 1987 rinker br. I guess ill have to do a compression test on it. but like I say, its a great running boat, what about a valve cover oil fille vent. Im not trying to hide the problem, but I would sure like to fish with it without spending any more money on it. I also have a chance to pick up a complete 120 hp 4 cyl mercruiser complete. How much trouble would the swap be. Thanx

 

[tobra100]

Re: oil blow by on mercruiser 470

by the way, the oil is fresh and not over filled.

 

[blasep]

Re: oil blow by on mercruiser 470

Just saw that this is an old post but, Ill reply anyway....I had the same problem with my 470 turned out to be the fuel pump. the diaphragm was old and cracked allowing fuel in the crankcase, fuel mixing with oil thinned the oil enough to blow by the rings and out the vent. new fuel pump ( and oil obviously) fixed the problem. I was worried that the cylinders were scored but she still has good compression and runs good.

 

[bruceb58]

Re: oil blow by on mercruiser 470

The original poster hasn't logged in since August of 2008 so I doubt he will se it.

 

[jsmallsb]

Re: oil blow by on mercruiser 470

I know this thread started about a year and half ago - but I could have written a lot of it. I just pulled a 1985 Glasply 19' with Mercruiser 170 from my Dad's barn in Washington. Hadn't been run in 15 years. No winterization, etc. 140 hours on engine/boat - beautiful shape.

Did the common sense stuff - yanked plugs - good until #4 cylinder, full of antifreeze. Sucked out antifreeze, lubricated all cylinders with Marvel (recommended from mechanic friend), turned over engine. Put in new plugs, etc and got it running. Runs great. After about 3 hours on engine, it starts blowing oil out the air vent next to the spark arrestor. Compression test shows 125 +- 2 on first 3 cylinders, 15 on #4.

Any thoughts short of complete rebuild??? Or any ideas on used Mercruiser 170 vintage 1985 (I'm in San Diego).

Thanks, Joel

 

[Don S]

Re: oil blow by on mercruiser 470

Start a new thread of your own, with your problems and what you have done. It's not a good idea to just start your thread on someone elses post, even if it is old. Your question will soon be lost and people will be replying to the original post.