To pull engine and repair, or to run it!

[sgtnoah]

Hello all. It's 2 degrees in Iowa, so possibly a strange time to think about boating... However my boat is in a heated garage and I'm starting to get optimistic that winter may in fact end at some point. Time to consider addressing an engine issue.

Boat is a 2005 with a 3.0 Mercruiser that I purchased last summer. In very good condition, always stored in a garage and appears to have very little use. Previous owner claims roughly 100 hours of use and I believe him do to next to no wear on the hull / vinyl / carpet.

The issue is this, the motor burns some oil. Roughly 1/2 quart per day on the water (4-5 hours of actual running, mostly at tubing speed). Runs smooth and has good power. Pulled the plugs, three have the nice tan color, one is a bit blacker. Not caked with carbon, but significantly darker than the others. Compression is good on all cylinders, I don't remember the numbers, but all are close to each other.

The question is this, could this be a result of the low use (possibly a stuck ring)?

It would be a financial stretch to have the engine pulled at this time, and I'm almost tempted to run it another year (50-75 hours) and then if things don't improve, put a long block into it. Is this a realistic plan?

Any thoughts or suggestions would be greatly appreciated.

-- Pete

 

[achris]

Get in with a borescope and see what the cylinder walls look like. If they look good, try some snake-oil type carbon remover... One of the best I've ever used is the Quicksilver 'Power Tune'.... Blast a bit in there and let it sit for 30 minutes or so, then fire up the engine and hopefully the carbon will be released...It might help, won't hurt....

Chris..

 

[tpenfield]

Yea, I think you need to do some more investigation and testing to figure out why you are losing oil. Also a compression test with the actual numbers and maybe even a cylinder leak test would be good.

I am assuming the seller did not tell you about the oil consumption issue . . . .

Are you getting the blue tinted smoke out of the exhaust?

 

[dozerII]

With it having such low use you may be right on the stuck "oil" ring, it may be carbon. I would be tempted to give it a good decarbing with Seafoam, then run a can or two in a tank of fuel to see if it improves. 1/2 a quart is a lot of oil, what kind of RPM are you running at, does it seem to be lugging, working real hard when you are pulling the tube? If it is it may have too much prop which would cause the overworking and possibly the oil burn.

 

[alldodge]

If motor checks out with what others have mentioned then I would pull the valve cover and check the valve stem seal. With so few hours and burning oil in one cylinder it might be that a seal was missed during original assembly by GM

 

[gm280]

I read this and wonder if you are really burning the oil or leaking it? If you are going through that much oil and it is burning, you should see the blue smoke out the exhaust. So if that isn't visible, look for some leak somewhere...

 

[Fastatv]

Many possible solutions have been recommended....fog or Seafoam for a stuck oil ring, possible damaged or missing valve guide/stem seal. Is the crankcase ventilation open and clear? Also, what viscosity is the oil your running in the engine? At least 15W40? Let us know what you do, whatever the fix was. Good luck!

 

[JaCrispy]

Typical valve stem seal it will smoke like mad upon start up then clear up some. You would also see traces of oil on the valve with the bad seal. Most can be replaced without removing the head, depending on your engine design.

 

[keith2k455]

I'd be more likely think leak....but where or how would have me baffled. If it were burning that much you should see and smell it. But if it's leaking, you should see that too. If you're burning that much oil the plug(s) should be fouled.

Don't pull the motor unless you're sure of the problem. Do you have a quick oil change drain plug that's leaking or open?

Man, my response is all over the place.....

 

[Alumarine]

Just curious. How do you check the oil? Do you let it sit level in the water for a bit?

 

[Scott Danforth]

A few thoughts

if you are truly burning oil, you will see it smoke when running on muffs.

this could be any of the above from a stuck ring to bad valve seal to a bad head gasket

A cylinder leakdown and pressure test should help you narrow down the culprit

head gasket can be changed with motor in boat
you can change the valve seals with just removing the valve cover with the proper tools.
stuck rings can be unstuck with a variety of chemicals

However if your headgasket has a breach between an oil passage and a water jacket passage, you could simply be pumping oil into the water. running on muffs an looking for an oil sheen in your driveway may help determine this, however you may need to pressurize the water jacket and do a leak down test there.

An external leak of oil will show up in the bilge.

 

[wrench 3]

I can't see a valve seal going through that much oil and not fouling the spark plug. But I have seen a broken oil ring use that much with almost no noticeable smoke.
If it is a stuck ring that you can't get free or a broken one, with those hours on it, I'd be more inclined to install a new set of rings insted of replacing the motor.

 

[sgtnoah]

Thank you all for the quick and logical replies!

I will try to answer the questions floated above.
- It does smoke, like it's on fire, upon startup. The smoke clears when it's up to temp, and is not noticeable from that point on.
- I check it on the trailer, in my garage, with the jack at the same height every time (approximating the level in the water).
- One of the the rocker arms was loose last season and making noise. I pulled the valve cover gasket and torqued the rocker to spec as per the manual. As far as I can remember, all of the valve seals appeared intact. I am a heavy equipment mechanic, so even though I wasn't looking at the seals, I hope that I would have seen if one was missing.
- Running 25-40 Oil
- Running mostly between trolling speed and 3500 rpm. Jaunts to 4600, but not sustained for long.

I will proceed with the advice that you all gave me, unless the above clues change your thoughts.

Thanks again!
-- Pete

 

[achris]

... so even though I wasn't looking at the seals, I hope that I would have seen if one was missing....

Yep, I'm the same... Only notice something when it's broken. If I didn't notice it, it must have been good.... Man, do I cope it from the wife if I don't notice something nice she's done.... I'm always in IT, the only thing that varies is the depth...

 

[MI-TY]

1/2 quart over a day of running and with the tell tale smoke upon cold start up would leave ME to believe you have a bad valve seal...or more than one.

A leakdown and compression test will not show evidence of a bad valve seal but will help in the process of elimination of the problem..as will a borescope.

I have heard of a way you can change valve seals on SOME motors by getting each cylinder to the point of both intake and exhaust valves being closed and pressurizing the cylinder with a modified spark plug hooked up to a compressor that you screw into the thread.

The air pressure inside the cylinder supplied by the compressor via the modified spark plug will hold the valves closed while you change the seals( providing your valves are not leaking).

It might be worth looking into it if you need to change them. Worst case scenario is you drop a valve and have to take the head off...if you succeed, you save hours of labor by not removing the heads.

 

[gm280]

For a quick see if valve seals would work, I'd try that. But I get the feeling it is more then just valve seals. It could also be valve guides and rings as well... But I'd certainly change the seal to see. That really isn't that big a job and equally doesn't cost much either. If you do go that route, make certain you don't drop a valve keeper down the oil return holes and into the valley area. Then you'll be removing the intake as well. Use some rags or something like that in the oil return holes while changing the seals. Let us know what you do and how it works out.

 

[Scott Danforth]

GM, its a 3.0, the keepers would end up in the pan.

 

[gm280]

GM, its a 3.0, the keepers would end up in the pan.

Yea, sorry. Sometimes I get reminiscing on my V8 days and forget what folks are working on...

 

[wrench 3]

I have heard of a way you can change valve seals on SOME motors by getting each cylinder to the point of both intake and exhaust valves being closed and pressurizing the cylinder with a modified spark plug hooked up to a compressor that you screw into the thread.

The air pressure inside the cylinder supplied by the compressor via the modified spark plug will hold the valves closed while you change the seals( providing your valves are not leaking).

If you do go this way, remove the rocker arms on that cylinder before you apply the air. The air will push the piston down to the bottom and, if the rockers are attached, open a valve. Also, if you tap down on the edge of the retainer before compressing the spring it will loosen up the keepers.
BTW a broken or stuck oil ring probably won't show up on a compression test.

 

[achris]

Yea, sorry. Sometimes I get reminiscing on my V8 days and forget what folks are working on...

Yep, been there... :facepalm: Lost count of how many times I've referred to 'timing chain and sprockets' with these in-line engines. :doh: