4.3L Mercruiser... Does This Make Sense?

wi4x4man

Seaman
Joined
Aug 25, 2010
Messages
55
Last weekend my son and I went out on Lake Superior with my 28' fishing boat. Everything was going just fine and we were having a great time. At any rate, I had been using the main (and only) engine to troll. Suddenly the engine just died out. It didn't bang, pop, or anything, just slowly died out. After trying to start it many times, I thought that perhaps the plugs fouled up. I pulled one out of the #1 cylinder, and it was full of carbon buildup. So, I figured I had found the problem. I was able to remove and clean all but 1 of the plugs due to the tools I had on board. I again tried to start it, but again I had nothing. It almost sounded like I had lost compression on two cylinders when I cranked it over. I had plenty of spark, fuel, and air, the only thing I figured I must be missing was compression. I checked the dipstick, and the level was about 1 inch higher than the full mark. The crankcase was loaded with gasoline. Thankfully a friend of mine was 12 miles away in his sailboat, and he towed me the 15 miles back to the marina.

So here is the question:

Could I have flooded the engine so badly, that it washed the cylinder walls down with gasoline and removed the oil on the walls? It somewhat makes sense that this might have happened, but has anyone ever heard of this happening or have had it happen to them? Without the oil to help the rings seal, I would have lost compression.

The engine in particular is a 4.3L Mercruiser with a 2 barrel carb.

I am in the process of getting a 9.9 Hp kicker for the boat so I don't use the main engine to troll anymore. Plus, it will help me keep my speed down from 3 mph to more like 1 or 1.5 mph as this is too fast for trolling anyways. Another major added benefit is that I will have another means of getting home.

If anyone sees any holes in my theory, or might have another explaination, please let me know.
 

Volphin

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Jun 5, 2011
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1,405
Re: 4.3L Mercruiser... Does This Make Sense?

I have run into this before. Not so much on I/Os but older pass cars. The oil has been contaminated by fuel, and fuel is a solvent. One thing is for sure... your crankcase is sparkling clean inside. You just created your own Varsol machine. :)

Seriously though, this is a very dangerous condition. Fuel vapors in the crankcase can ignite causing a fire. First, pull that old mechanical fuel pump off and toss it. Drain the crankcase of contaminated oil. Let it stand with the drain plug out, dipstick removed, oil fill cap off, and rubber hoses from the valve covers off. Remove the oil filter and toss it. Let stand for 4 hours in the sun, and keep all sparks and open flame away from the vessel. After 4 hours, blow compressed air through open passages if you have an air compressor. Use your nose. Does it smell like fuel still? Let stand some more. When you are satisfied that residual fuel has evaporated off, reinstall a new oil filter, hoses, etc. Refill crankcase with 30w even if it calls for multi viscosity oil. Plate off that fuel pump housing. Replace the fuel pump with a quality electric one... Holley marine makes some good ones that are USCG approved and have venting to the flame arrestor.

Now disable the coil by removing the two wires at the coil. Crank the engine for 30 seconds at a time until you get an oil pressure reading. Rewire the coil and start the engine. Run engine on muffs until operating temp is reached. Be aware that you may have spun a bearing, but usually these engines are pretty robust. So be on your game listening for anything odd. You may still hear some clacking at startup however.

Once she reaches operating temp, allow engine to cool for a bit, then drain the oil. Refill the crankcase with proper oil. Test on the water. Hopefully all will be good to go. :)

Sorry so long...

V
 

wi4x4man

Seaman
Joined
Aug 25, 2010
Messages
55
Re: 4.3L Mercruiser... Does This Make Sense?

Well, the engine is brand new... Actually, it is a Mercruiser reman longblock. I may have a whole 15 hours on it. It was originally set up with a mechanical pump, but I did remove that and I put on a Mercruiser electric fuel pump.

I have also drained the bad oil. I cannot get to the stupid oil filter without removing the port manifold. I am in the process of investing a remote oil filter kit for it. When I first put the filter on, the engine wasn't even in the boat. I do plan on taking the existing filter out and replacing it. It is just a matter of having the time to do it.

So let's say that I get it nice and cleaned out of all of the fuel. Would it be logical that without oil on the cylinder walls, that this is the reason I cannot develop compression? I have not put my compression gauge on it yet, but you can definitely tell that it doesn't have compression on a few cylinders when it cranks. My guess, is that it has lost compression on at least two cylinders.

The unfortunate thing about this arrangement is that the engine is deep inside the hull. If I had an arm that was about 3 feet longer with about 5 extra joints, and was about 2" in diameter the entire length, I think I would be in good shape. But before I decide to yank the engine, I want to see if this could be a plausible explaination.
 

Evinrude Boater

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Jul 6, 2004
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1,143
Re: 4.3L Mercruiser... Does This Make Sense?

Measure the compression then you'll know the state of the engine. Is it still within the warranty period?
 

cliffblue

Petty Officer 1st Class
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Oct 26, 2010
Messages
209
Re: 4.3L Mercruiser... Does This Make Sense?

I can dig needing to be built like a broom stick to get to the sides and bottom of your engine. I wonder if the hydraulic lifters have collapsed, not letting the intake valves open? They would probably pump up with good oil in her.
 

wi4x4man

Seaman
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Aug 25, 2010
Messages
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Re: 4.3L Mercruiser... Does This Make Sense?

Yes, the engine is still under the warranty period. But I just do not think that there is anything "wrong" with the engine. I think it was me that may have made the critical errors. From running at idle for an exceessive period of time to the constant starting that I tried to get it going again when I was stuck out on the water.

As for the lifter idea, that might be a possibility.

Hopefully today I will be able to get something done with her as long as the rain holds out.
 

Evinrude Boater

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Re: 4.3L Mercruiser... Does This Make Sense?

You're not supposed to idle it for long periods of time during the break-in period and at 15 hours you're still within the break-in period.
If it has lost compression in only two cylinders then I don't think your starting attempts caused this. All cylinders should have compression, oil just brings it up if there's cylinder wall or ring damage.
 

wi4x4man

Seaman
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Aug 25, 2010
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Re: 4.3L Mercruiser... Does This Make Sense?

When I talk about excessive idling, I am talking about a whole 2 hours. Could that have really made the difference?

I am most familiar with Diesel engines, and running a diesel at low loads or no loads can cause problems such as wet stacking (blow by) and what's worse, cylinder glazing. I was under the impression that gasoline engines were a little bit different.
 

Volphin

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Jun 5, 2011
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Re: 4.3L Mercruiser... Does This Make Sense?

No, you would still have some compression even after a 2 hour idle. All the break in period is designed to do is keep the rings from getting stuck in their grooves. Oil or not in the cylinders, there will be compression, as long as the lifters and cam are operating properly. The carb dumped that much fuel in your crankcase? It must be pouring out of it!

Can you pull a valve cover fairly easily?

V
 

wi4x4man

Seaman
Joined
Aug 25, 2010
Messages
55
Re: 4.3L Mercruiser... Does This Make Sense?

The only way to pull the valve covers is if I loosen the manifolds so I can tip them out and then take the shifting linkages, hoses, thunderbox, and etc off.

Keep in mind that it did not make any bad noises when it quit. It simply shut off and that was all there was to it.

In terms of fuel in the crank, yes, it was pretty full. The level was about 1.5" above the full mark. When I drained it, the oil smelled like fuel, not oil.

Hopefully tomorrow I will be able to fiddle around with it. Picked up a kicker motor today, otherwise I would have worked in it.
 

CharlieB

Vice Admiral
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Apr 10, 2007
Messages
5,617
Re: 4.3L Mercruiser... Does This Make Sense?

Have you checked the carb for flooding?

Turn on that new fuel pump and look down the carb throat to see if any fuel is flowing.

IF, any piston rings damage is caused by excessive fuel washing I doubt if the reman warranty will cover it.
 

ohioriverat

Petty Officer 2nd Class
Joined
Aug 7, 2011
Messages
115
Re: 4.3L Mercruiser... Does This Make Sense?

in my opinion this motor should be replaced cause the gas washed out the cylinders,even if the valve problem is fixed i would not trust it.
 
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