Spark plugs: Merc 3.0L vs. 3.0LX

[Mile-High Mariner]

1992 Mecruiser 3.0L, S/N:0D805131<br />The previous (original) owner of my boat thought it was powered by a 3.0LX (wishful thinking, I think) and so used plugs and other maintenance items consistent with this belief. I'm dealing with a potential burned valve issue and in trying to determine the cause I'm wondering if there is enough difference in the heat range of the plugs recommended for the 3.0LX vs. the 3.0L to have contributed to a burned valve in cyl. #2 (due to preignition). When I bought the boat, I observed an appreciable amount of carbon on the pistons, but only #2 yields low compression. I've removed a substantial amount of the carbon and I'm going to try out an intriguing hydrodecarbonizing technique (thanks, Bondo!) to see if I can't get some more off before I pull the head (thanks, Don!) and have it rebuilt, if the tolerances are acceptable. Thanks for your help!

 

[Bondo]

Re: Spark plugs: Merc 3.0L vs. 3.0LX

Hi Dave,.......<br /><br />I've explained that process Here Too........ <br /><br />I Don't Think your theory going to hold Water,..... <br /><br />Different Sparkplugs Ain't going to Burn just 1 Valve............And,.. I'm Pretty Sure those motors use the Same Plug Anyways.......<br /><br />Here's Another Theory,.......<br />The motors been running Way Too Rich,..... Excess Carbon, Right,........<br />Either the Valve, or the rings are just Overly Coked Up,+ If a valve was Held Open Slightly by Carbon,.....<br />Then it would be Severely Burnt in No Time........<br /><br />Run a Qt., or 2 of Water Thru it,+ Pull the Head,.......<br />Then you'll have a Nice Clean Motor,+ Know Exactly What's Wrong.............

 

[Trent]

Re: Spark plugs: Merc 3.0L vs. 3.0LX

Parts manual for the 3.0/3.0LX calls for the same sparkplug.<br /><br />If Bondos water trick dont work (iv used if for years also) try staking the valve. Remove the valve cover and make sure the cylinder your working on is either at TDC or BDC and then hit the valve with a rubber hammer. This is to break loose any carbon between the valve and the valve seat. This proceedure works sometimes but not all.

 

[Don S]

Re: Spark plugs: Merc 3.0L vs. 3.0LX

I will check the serial number for your engine and possibly find out if it is a L or LX. But the plugs are different for the 2. The 3.0L calls for an NGK BR6FS, while the 3.0LX calls for BPR6EFS which is a long reach plug. If you have either the EST Distributor, or the Digital ignition.<br />If you have the points distributor, then you only choice is the BR6FS.<br />Wrong timing and lean burning causes more valve problems on the 3.0 engines than anything else. Especially if you have the EST ignition and it was not set correctly.

 

[Don S]

Re: Spark plugs: Merc 3.0L vs. 3.0LX

Was able to check out your serial number.<br />You have a 3.0L, NOT have a 3.0LX<br />You do have an EST distributor, and you do take the BR6FS NGK plug, or an AC MR43T.<br /><br />Here is all the numbers for engine, drive and transom shield in your Stingray.<br />ENG: 0D805131 430B100ES 1992 MERCRUISER 3.0L ALPHA I <br />DRV: 0D677154 5010198ES 1992 MERCRUISER ALPHA 1.98:1 <br />TRN: 0D694897 6010000ES 1992 MERCRUISER ALPHA TRANSOM

 

[Laddies]

Re: Spark plugs: Merc 3.0L vs. 3.0LX

The ID number stamped in the block by the distributer will tell if the engine left the factory as a L or LX, A, L engine ends with-RM or RJ and a LX ends with-RN or RK

 

[Bondo]

Re: Spark plugs: Merc 3.0L vs. 3.0LX

Has anybody here had a couple of Heads off these 2 motors on the Bench,+ Looked at them,.??...<br /><br />I'm Wondering if the LX version is the Vortec style combustion chamber,..??.....<br /><br />The difference in the NGK plug #s leads me to believe this.......I Haven't Seen 1.........

 

[trog100]

Re: Spark plugs: Merc 3.0L vs. 3.0LX

for a short period of time 89 to 94 i think.. merc "depowered" the 3.0L by fitting it with the discontinued (from 89) 2.5 engines cylinder head.. this supposedly put the 3.0L in the same 115 horse power slot the 2.5 used to occupy..<br /><br />personally i recon this was more about keeping a nice neat power range line up and useing up old parts than the real horse power of the ex 135 hp now supposedly 115 3.0L..<br /><br />the LX was just the old 3.0L fitted with electronic ignition i think.. its the 89 to 94 3.0L thats the odd one out..<br /><br />after 94 sanity prevailed and the hybrid so called 3.0L 115 hp 3.0L block/2.5 head combination dissapeared.. and the 3.0L became just a 135 hp 3.0L again complete with its "real" cylinder head.. <br /><br />as don says one of em used short reach plugs.. i think it was the hybrid.. these would have been the same plugs as used in the discontinued 2.5 engine for obvious reasons..<br /><br />either way its got nothing to do with your valve burn out problem..<br /><br />trog

 

[Laddies]

Re: Spark plugs: Merc 3.0L vs. 3.0LX

Bondo, the two heads have a different style combustion chambers the LX is amost oval and I think a little deeper, but never had both styles off side by side to compare

 

[Mile-High Mariner]

Re: Spark plugs: Merc 3.0L vs. 3.0LX

Don - thanks for all the S/N info, etc. BTW - my engine is equipped with the Delco EST ignition, and the module was not producing the specified advance when I first checked it out, so the retarded timing certainly had something to do with the problems I'm attempting to cure now.<br /><br />Bondo - theory won't hold water, but at least the boat still does! I don't think the BRP6EFS is hot enough to make a difference, either, and I don't think it's long enough to risk mechanical contact with the piston, or I imagine it would have resulted in catastrophic damage long ago, while the original owner had them in there. On the upside, he was foaming-at-the-mouth rabid about maintenance and documentation, so I have notes on just about everything he ever did or had done to the boat.<br /><br />Trent, Laddies & Trog - thanks for the tips, boys! I benefit daily from the things I pick up from you guys - too bad we can't all get together over a cold one (or a hot cup of something - it's 13*F here in western Colorado right now!) every now and then!<br /><br />I'm glad my question has brought up so much good discussion! My e'mail exchanges with Mercruiser customer service indicate that the block is the same - the head and manifold and certain other peripherals are the differences between the L and the LX motors.