Mercuiser 4.3 smoke coming from propeller

[easyloader]

I have a 4.3 mercruiser with EFI which has smoke on start up and coming from propeller when running. I'm burning some oil but not an excessive amount. I'm running 4 quarts of Rotella 15-40 oil with a quart of lucas oil stabilizer. I took the plugs out for a compression test and they are wet with a tan color. Compression has a high of 140 low 125 and 4 cyclingers 130- 135. I added three squirts of oil to each cyclinder and most cylinders psi increased by 15. The test was done with the engine cold and 85 degress outside air temperature. There doesn't seem to any smoke coming from valve covers. The motors idle is smooth and the boat has plenty of power. I'm planning on doing leak down test at the end of the season. Any ideas?

 

[thumpar]

What color is the smoke?

 

[easyloader]

light gray/white

 

[thumpar]

White smoke would normally be water steam.

 

[ricohman]

Maybe you are burning some water off from some other problem? Exhaust that has oil in it is pretty distinctive.
Its possible to still have great compression and burn oil if you have fractured oil rings.

 

[easyloader]

After reading the replies and thinking about it, it's not white smoke or steam it's oil . Did have water in motor last year and motor was seized. Freed the motor replaced bent intake valve, manifolds and flappers. If rings are fractured will it be picked up in a leakdown test? I can perform the test at top dead center and other piston positions with the push rods removed so that the valves are closed?

 

[thumpar]

You may not be able to tell it is broken rings but you would be able to tell if it is ring/piston related or head problem. Don't take anything apart until you do all the diags you can.

 

[easyloader]

I agree. Plus running to good to shorten season. i don't like not be able to solve a problem and really want to figure it out and then decide if I should repair it. if I had fractured rings is there a possibility the rings could break and destroy the motor? I

 

[Bondo]

Ayuh,.... A compression, 'n leak-down tests will point ya in the right direction,...
You'll be able to take notice of the spark plug colors as well,....
If it's oil, a plug or more oughta be black, carboned up, 'n sooty,...

 

[easyloader]

ok, sounds like the compression test and color of plugs didn't turn up any issues. I'll do a leak down test next month and if nothing turns up change valves seals because of smoke on start up. Plus I always wanted to do valves seals and it's only fifty sixty bucks to do it.

 

[alldodge]

The motors idle is smooth and the boat has plenty of power.

Engine fires right up, idle is good, plenty of power, but smokes a bit during initial start up. Slight sign of wet plugs.

I don't see a problem which really needs to be fixed

 

[ricohman]

While a leakdown test won't show busted oil rings, you say it was seized? Its not uncommon for any engine that was once seized to smoke. Compression rings get stuck (which will affect the compression) and cylinders get scored. If its running well maybe just use it and tear it down during the winter. If you need a rebore and its running well I can't see it affecting anything in the long term and you will be going over bore anyway.
I've torn down engines with various busted rings and found varying amount of scoring. Nothing that an overbore couldn't fix though.

 

[airdvr1227]

Engine fires right up, idle is good, plenty of power, but smokes a bit during initial start up. Slight sign of wet plugs.

I don't see a problem which really needs to be fixed

Agreed. I've seen old DC3s that smoked on start-up. That's how you knew it had oil.

 

[easyloader]

thanks everyone not going to do anything to drastic