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Old 05-12-2016, 11:51 AM
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Definitive Answer: Correct Spark Plugs for 5.7L MCX

I have a 2004 X-30 with the 5.7L MCX Vortex EFI (non-CAT) engine. I'm replacing the plugs and searched all over the board for the correct plugs and gap. What I found was confusing, so I reached out direct to Indmar. Here is the response I got, FWIW.

Bottom line up front: The standard MR43LTS spark plugs gapped at .045”; tightened to 11 foot lbs of torque.

**Note: this is a change from the factory and most manuals printed at the same time as the boat was produced....Here's the full response...

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Your engine probably came from the factory with AC 41-932 plugs which have superseded to 41-993 and now to 41-101. The 41- plugs are platinum or iridium plugs. Your 2004 model engine is a pre-catalyst model, therefore you would not see a benefit in using platinum or iridium tipped plugs. Platinum or iridium plugs operate best when they operate hot and lean and your pre-catalyst engine runs relatively cold and rich.



Even though it contradicts the Operator’s Manual for your engine, I would recommend that you use the standard MR43LTS spark plugs gapped at .045”. The standard plugs are less expensive and tolerate the cold and rich operating characteristics of your engine better than the platinum or iridium plugs do.
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Old 05-12-2016, 12:06 PM
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Good info. Thanks for sharing with the forum.
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Old 05-12-2016, 12:07 PM
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CantRepeat CantRepeat is online now
 
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Great post!

I think most people were in agreeance that non CAT MCXs were MR43LTS spark plugs gapped at .045 and that CAT motors took the other plug gapped at .060.
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Old 05-12-2016, 03:33 PM
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Geesh, right after I just put in a set of 41-993, which were $7 each.
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Old 05-12-2016, 03:39 PM
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Quote:
Originally Posted by 76S&S View Post
Geesh, right after I just put in a set of 41-993, which were $7 each.
Exactly! I'll be returning my $55 worth of spark plugs I bought for set of 8 at $2.20 a piece. Nice!
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Old 05-12-2016, 03:48 PM
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got to be careful of the engine manuals... my MC manual said .045 gap when actual needed to be .030. Clymers has MR43LTS gapped at .045. When I gapped my plugs at .045 I wore them out in 66 hours..
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Old 05-12-2016, 05:54 PM
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I pulled a set of 41-932 (platinum or iridium) plugs, gapped at .065 out of a boat recently that were over 10 years old. They looked good and the boat started as soon as you hit the switch. The owner went back with the 41-993 since the others lasted so long.
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Old 05-12-2016, 07:35 PM
KyleNowad KyleNowad is offline
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This plug issue for the MCX has got to be one of the biggest mysteries in boating.

I'm glad we are getting some clarification. Now hopefully SEO will work in your favor and you can help the world with this common problem.
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