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Old 09-05-2010, 03:43 PM   #1
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Question How much smoke is normal on a Mercruiser 5.0L TKS?

Not too familiar with carbed engines, last boat was EFI. When I start up after the engines have been cool for about 6 hours or more, there is a noticeable amount of exhaust smoke (its white/gray in color) for the first 5-8 minutes or so. Once the engines are warmed up, nothing.

I don't really mine out on the water, but its kind of annoying to smoke out my neighbors at the docks or tied up with other people.

Several mechanics have looked at. First one said someone had filled the engines with too much oil and it was the excess burning off. Had it filled to the correct amount at the next oil change, no difference. Next one said it was oil residue left in the oil pan and needed to burn off every time the engine was cold - nothing I can do about.

I can't believe this is normal as it is quite a bit of smoke for a while. Any other thoughts on what could cause this?

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2006 Maxum 3100 SE - twin 5.0L TKS
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Old 09-08-2010, 12:26 PM   #2
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I'd expect too much oil to be bluish in color, not white/gray. Steam is white/grey, for exmple. My old 454 used to do the exact same thing before it blew. I'm not saying your about to blow your engine.
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Old 09-08-2010, 02:03 PM   #3
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Quote:
Originally Posted by jmax View Post
Several mechanics have looked at. First one said someone had filled the engines with too much oil and it was the excess burning off. Had it filled to the correct amount at the next oil change, no difference. Next one said it was oil residue left in the oil pan and needed to burn off every time the engine was cold - nothing I can do about.
You need to find new, 'er, educated mechanics J. As Shrew pointed out, if the engine is burning oil, the resulting cloud will blueish.

The first mech is semi correct. Too much oil in the engine can result in excessive amounts of oil on the cylinder walls - overwhelming the rings and getting into the combustion chambers and burning. But the smoke will be blue, not white/gray.

If the second one really said it was "residue left in the oil pan and needed to burn off every time the engine was cold", well - he's just stupid, or assumes you are. The oil pan is were the oil pump picks up the oil and circulates it, and the circulated oil drains back to the pan - it must always have oil in it.

If indeed the engines were over filled resulting in burning oil, once the level is reduced the engines should stop burning oil very quickly. I'd say a 30 minute cruise at 25 knots would do the trick.

Unfortunately, the symptoms don't match the diagnosis. If the smoke is truly white/gray the engines are either running very very "rich" (the gas/air ratio is off) or the engines are ingesting small amounts of water.

Are you absolutely certain it's BOTH engines? If it is both, did the symptom start at exactly the same time on both? Was it a gradual increase or was it more like a light switch; no smoke then bam - smoking like a train?

Dan
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Old 09-08-2010, 04:56 PM   #4
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It is definitely both engines. They have been doing this since I have owned the boat (last summer, and this summer). When I took ownership of the boat one engine had 7 hours on it (brand new, merc replaced under warranty), the other had 70 hours on it. The dealer ran the hour meter up on the new engine to match the other factory engine @ 70 hours each. They are now both at about 200 hours.

At first I chalked it up to carbed engine since I was used to an EFI in my previous boat. And the fact that it stops once the engines are warm made me not lose too much sleep over it. However, since it has continued I am starting to wonder what the deal is.

I mis-spoke when I said the smoke was white... it is certainly much darker. I can't say for sure that it is blue, but definitely some shade of dark gray. It is consistent whenever I start the engines from cold. Smokes for 5-10 minutes and stops once the engines hit 150-160. No smoke is visible at all after that point while running. If I stop and restart after sitting for a short period of time (engines still warm), there is no smoke.

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Josh
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Old 09-08-2010, 06:49 PM   #5
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It was doing this when you bought the boat? So, next question Josh, were the engines over-filled with oil when you took ownership? Even if they were, when the oil levels were returned to normal, they wouldn't still be burning oil.

Since you say it's embarrassing I have to assume they are producing a bit of a cloud at cold start. If that's the case it should be fairly evident what color it is and, if it's oil, you should be able to smell it as well. For that matter, if they are running rich you should be able to smell that too.

"Certainly much darker". If the smoke is indeed darker than white (white = burning water) and has no blueish tint to it (blue = burning oil) the only other thing it could be is that the engines are running very rich (too much gas) when first started. And since you state that it clears up once the engines get to operating temp, my first guess is that the chokes on both carbs are misadjusted.

It is odd that they both exhibit the same symptom, which leads one to search for a commonality between the two. However, each has its own support systems (fuel pumps, filters, cooling pumps, ignition systems, carbs, etc). Most of those are not adjustable, and I find it unlikely that the problem happened to both engines at the same time. Except the carbs. Get one "mechanic" in there that thinks he knows how to adjust one, and does the same to the other.....well, you get the idea.

I guess the first course of action is to verify smoke color so you do not chase a non problem. If smoke color is confirmed to be anything other than tinted blue I would then pull some spark plugs from both engines for inspection. Two from each side of each engine. The porcelain unsulators near the tips should be a light tan color, and the center electrode and the side ground strap should be pretty black, but not caked with crud or sooty. They should all look pretty much the same. Crud or soot indicates a rich mixture. Excessive crud could mean oil. if they are white, and appear very clean, they are indeed being steam cleaned from small amounts of ingested water. Take a couple of close up's and post them here, but this link contains good pictures: http://www.triumphspitfire.nl/plugs.html

Dan
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