MCX using a lot of oil
Last week we made our fall trip down to Lake Mead. I checked the oil before we left - it didn't registered on the dipstick! (2006 X30 w/MCX - 212 hours) I had to add about 1 1/2 quarts to get it in the middle of the operating range on the dipstick. Probably had about 50 hours on it for the summer at that point. I started to winterize it Tuesday night and when I drained the oil I got 3 quarts out of it plus whatever was in the filter (I use a high capacity Mobile 1 filter) - maybe 1/2 quart? So in three days at Lake Mead I burned a quart?! We were doing some cruising at 5000 - 5200 RPM's (at that lower elevation I could go above that but was careful not to - I need a higher pitch prop for Lake Mead and Lake Powell). We also did a good amount of tubing (three man, both solo and doubled up) as well as some skiing and hydrofoiling.
Well, that seemed like a lot of oil to burn in just a few days so tonight I did a compression test (engine warmed to temp, all spark plugs removed, fuel injectors disabled) with the following results:
Owners manual says minimum compression is 100 with no greater than 70% difference from high to low. At 145, my low is 84% of the high. According to the manual I'm fine. I've always heard 10% between high and low - I'm at 16%. SHOULD I BE WORRIED? Could cylinders 3 & 5 be causing my high oil consumption or were all 8 consuming it due to my high RPM loads?
Other info that may be helpful:
No noticeable smoke at start up.
No noticeable oil slick on the water when idling or oily residue on transom when removed from water.
No noticeable smoke when cruising at high speed.
Oil removed from engine was not milky.
No noticeable oil anywhere in bilge or on engine.
Any input from you mechanics out there would be much appreciated!
I have a 2006 MCX and I also use the MOBILE 1 High Capacity filter: It takes 6 quarts to get to the top of the dip stick. I have never put more than 1/2 quart at anytime , usually after about 25 hours.
Did your spark plugs look clean? Maybe replace your PVC valve? Look at your air filter and see if has oil in it.
I agree that would be too much oil in that short of time, I would suspect if the engine was burning it you would see smoke consistently.
If elevated oil burn was occurring in 1 or 2 cylinders, I would expect to see it on the sparkplugs.
There should be no more then +/- 10% difference between the lowest and highest readings.
In your case, if I math this up correctly.
% difference = 100 - (172 / 145 * 100) = 15.69%
This is greater then the standard norm of +/- 10% so you do have a problem some where. I would couple this test with the fact you used 1.5+ quarts of oil in 50 hours.
You can do a wet test to isolate the issue to rings or valves.
So the 64k question is how long can I run the motor like this?
I don't know. It could continue to run ok for a long time or it could get worse in a couple of weeks.
Maybe enginenut will be around to give more guidance.
I actually did do a wet test - should have mentioned that.
When I put a few squirts of oil in cylinders 3 & 5, they both increased by about 15 lbs, bringing them to 165 & 160. Leaking rings, right? Both of those plugs were a bit darker than the others - I'll post pictures later. So, as has already been mentioned, is that worth pulling the engine or just keep an eye on my oil level? And how could I have such a problem with so few hours on the boat?
Here are photos of the plugs. Two shots of plug#5.
There are a lot of things that can cause rings to go bad.
Too much back pressure
Leaking injectors diluting the oil, causing scuffing to the cylinder walls
Low oil or low oil pressure
Not changing the oil/filter
Are you the original owner?
As far as pulling the motor, well, I don't know. Clearly there is an oil consumption issue and that is not going to change.
What you don't want to do is mess up the cylinder walls so badly that you need to go 60 over on a first rebuild. At this point, if you pull it, you might get lucky and only need to hone the cylinders and and put in new pistons and rings. But, you wont know that until it's apart.
Bad news doesn't get better with time.
From those photos 3 and 5 clearly have blow by.
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