Mercruiser 898 Spark Plug Problem

[greg82255]

Hello again,

After my last thread of asking everyone what type of spark plugs to use, I went out and bought some NGK plugs. When I went to take the old ones out, the # 1, 3, 5, and 7 cylinder plugs looked alittle dirty, but still OK. The # 2, 4, 6, and 8 cylinder plugs had crap all over them. Does anyone know what may be causing this, and what I could do to fix it? The pictures I included are of the #2, 4, 6, and 8 cylinders. One of the plugs was even broken (electrode broken off?). Its possible that I did that while taking it out, but I don't think so.

 

[JustJason]

Re: Mercruiser 898 Spark Plug Problem

Looks like you have a water ingestion issue on the left bank.

How old/hours on the motor. Is it a salt or fresh water engine? Any water in the oil?

 

[Bt Doctur]

Re: Mercruiser 898 Spark Plug Problem

The plugs are too long and too hot of a heat range for the GM motor, what type are they.

 

[greg82255]

Re: Mercruiser 898 Spark Plug Problem

I bought new plugs, replaced them with the NGK BR6FS. The ones in the picture are Champion RV19C. I got them from a guy at Pep boy who looked them up in a book. Big mistake, I know.

JustJason, The motor is a 1982, but I replaced the intake and carb last winter. 12 hours this year since the new intake and carb, new oil before I used it this year. I am changing the oil again tomorrow and will check for water in the oil. I assume a water ingestion issue would come from improper sealing of the intake manifold?

 

[greg82255]

Re: Mercruiser 898 Spark Plug Problem

It just occurred to me.. I pulled the dipstick today to check the oil level and I did not see any milky oil. I am not sure if this is an accurate indication of whether the rest of the oil is milky, I will check tomorrow. In the meantime any other suggestions would be greatly appreciated, I seriously hope it is not a water ingestion problem.

 

[greg82255]

Re: Mercruiser 898 Spark Plug Problem

Any thoughts? I am going away for the weekend with the boat and I'd like to get this resolved before that..

 

[Bondo]

Re: Mercruiser 898 Spark Plug Problem

Ayuh,... It could be water ingestion into the combustion chambers causing the Clean plugs,...
In that case, it may not be getting into the oil...
Or,...
The missing electrode is probably a sign of Detonation...

 

[greg82255]

Re: Mercruiser 898 Spark Plug Problem

So where should I start to check for problems? How can I check for water ingestion into the chambers? I assume this is not a quick fix..

 

[greg82255]

Re: Mercruiser 898 Spark Plug Problem

I replaced both the intake and exhaust manifolds over the winter, so I bet it is one of the seals there. The riser is easier to pull off than the intake, so I will start there.

Just curious, how would a leak from the exhaust manifold to riser cause the plugs to look the way they do? I believe you, I just do not understand how it works.

 

[greg82255]

Re: Mercruiser 898 Spark Plug Problem

Also, when I pull the riser and/or intake, what am I looking for?

 

[JustJason]

Re: Mercruiser 898 Spark Plug Problem

What part of boston are you from? In the city itself or 1 of the burbs?

how would a leak from the exhaust manifold to riser cause the plugs to look the way they do? I believe you, I just do not understand how it works.

Hmmm, I wouldn't start with the exhaust side, I would start on the intake side of things. Epecially given that you stated you changed the intake manifold.

It's not common to see clean plugs on a full bank with a sterndrive engine. Usually you'd see it in 1 or 2 cylinders, all cylinders, but not an isolated bank. But uncommon does not mean impossible either.

Does this engine have raw water or fresh water cooling?

Whats happening is water is entering the cylinder/combustion chamber while running. It may be comeing it on any part of the 4 stroke process, or all parts. It's just enough water to flash to steam inside of a hot cylinder, but not enough water to hydrolock the motor. When water flashes to steam it steam cleans everything inside of the combustion chamber, including the insulators on the plugs. Spark plugs should come out looking a little dirty, they can be many different colors with light mocha being the best, but when they come out white they are being cleaned.

Easiest way to check is throw in 4 dirty old plugs on the suspect bank, run the engine, if they come out cleaner than they went in you confirmed the diagnoses Dr House style.

BTW, don't get advice on boat motors from autopart store guys... they have no idea what they are doing. NGK plugs are fine if you get the correct part. But stick with AC MR43's, that's what a 305 really wants for plugs.

 

[greg82255]

Re: Mercruiser 898 Spark Plug Problem

I am from Andover, MA. About 20 miles north of Boston.

The engine is fresh water cooled? I thought raw and freshwater were the same thing, guess not.. Water comes in through the sterndrive and circulates out the exhaust, whichever one that is lol.

So just to be clear - The leak is on the side where the plugs are clean, not where they are dirty?

How long should I run the engine once I put the dirty plugs in there? Should a few minutes be enough to see if they are clean? Once I determine that there is infact water getting into the chambers, I will pull the riser. What am I loooking for when the riser is off? Should I just reseal it and see if that fixes the problem?

 

[JustJason]

Re: Mercruiser 898 Spark Plug Problem

If the engine has a closed cooling system, with a heat exchanger and antifreeze it's a freshwater cooling system. If seawater circulates through the engine and exhaust and dumps back out it's a raw water cooling system. Gotta love the terminology.

So just to be clear - The leak is on the side where the plugs are clean, not where they are dirty?

Yes, it is the leak that is causing the plugs to become clean.

How long should I run the engine once I put the dirty plugs in there?

Eagh... 1/2 an hour ought to do it, but that's with the boat in the water and under a load, not on a garden hose.

I will pull the riser. What am I loooking for when the riser is off?

I know Bubba said riser, but I don't agree with him on this one. Riser is exhaust, exhaust is after combustion. It is water getting in pre or during combustion that's cleaning the plugs. That has nothing to do with the exhaust system, that's all after the fact.

Have you done a compression test yet? If so, what are your numbers?

Another thing to try is to pull all 8 plugs, hook up a water source (garden hose + muffs), disable the ignition system and crank the engine over. 10 seconds of cranking, 30 seconds of off time, are you getting any water out of the spark plug holes?

I would start with that before I started pulling the manifold or head.

 

[greg82255]

Re: Mercruiser 898 Spark Plug Problem

I'll do the compression test later today, when I get home from work. What should the numbers be for my engine?

I will also pull the plugs and crank the engine over like you suggested.

I was planning on going up to lake Winnipesaukee this weekend with my boat. Am I going to do any damage to the engine if this problem is not immediately fixed? I have had the boat in the water for about a month now and everything seems to run fine..

I assume this problem is costing me some power too? My top speed is 3ish MPH less than it was last year, thats after adding a holley 4 barrel and Edelbrock performer intake..