Spark Plug Choice - Mercruiser 7.4 LX MPI

[tpenfield]

This may be a question more for folks like Don S or Bond-o , but I thought that I would put it out in the forum for everyone's input.

So, when I bought my boat last Fall (see signature below for info), the surveyor that I used pre-purchase (who is accredited by SAMS in both 'vessels' and 'engines') noted that the spark plugs should be replaced. He mentioned that in his experience, the GM-based engines seem to run best on the AC Delco brand of spark plugs, and recommended those versus Champion or NGK.

I'm OK with that, but I wanted to see if other folks in the boating world have seen much difference between spark plug brands. I have used NGK for years, because they are quite market prevalent, and have also used Champions. Don't recall using AC Delco.

It looks like my engines take Mercruiser P/N 33-898264001 spark plugs, which is an "AC Delco MR43T" or a "NGK BR6FS" . . . not sure about the Champion equivalent.

 

[Bondo]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

He mentioned that in his experience, the GM-based engines seem to run best on the AC Delco brand of spark plugs,

Ayuh,... I feel the same way as yer surveyor,....

ACs in a GM,...

Autolite/ Motorcraft for a Ford,...

NGKs for Jap motors...

 

[Don S]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

AC is what comes in the engines from GM when brand new from the factory.
I have had good luck with AC and NGK on marine engine, poor luck with Champion, and wouldn't degrade a GM engine by putting a Ford plug in it.

We used a lot of NGK when I lived in Alaska, because we couldn't get AC from Merc or Volvo at the time, and our local sources didn't have AC, but did have NGK
Merc also sold NGK to dealers.

When I moved down here, the place I worked at carried the full line of NGK, but not AC. So guess what we used.

 

[MarkSee]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

This may be a question more for folks like Don S or Bond-o , but I thought that I would put it out in the forum for everyone's input.

When I have my "mechanic" dreams Ted, I tend to be carrying a tool box for Don, Chris or Bondo so is that close enough?

For both my 7.4 and the 4.3 when I owned it and went to the best Merc dealer in my area, his look-up showed that NGK is what was specified as the current replacement.

Mark

 

[achris]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

Although it's a bit like an oil thread, fill in the blank, "I use _____ brand of oil and have never had a problem", spark plugs are similar with one notable exception, Champions. Almost everybody in the world has, at some point in time, been let down by a faulty champion spark plug....

Like the guys above, I use NGK... Easier to get locally for me too...

JMHO,

Chris......

 

[RogersJetboat454]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

"Keep your GM all GM"

IMHO, Champions belong in lawn mowers, Chrysler products, and are handy for when your painting an engine....

 

[achris]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

IMHO, Champions belong in lawn mowers, Chrysler products, and are handy for when your painting an engine....

What have you got against lawn-mowers?

 

[Oshkosh1]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

The previoius poster(s) omniscience being evident is enough, however I will add my 2?...
A/C's in anything GM...
Motorcraft/Autolite in Ford...
Bosch for newer/Champion for older Dodges...
NGK in Jap(Car/Sleds/ATV's)
Champion in Briggs/Tecumseh/Kohler small engines.

 

[Oshkosh1]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

What have you got against lawn-mowers?

Lol!!
Although I'd normally agree...I'm willing to bet that if I just walked around my "neighborhood" and pulled the ignition wire off the mowers/blowers/tillers/tractors and weed whackers I'd find the dreaded "C" word written on 90% of the plugs!

I'm not a big fan of them in anything with more than two cylinders, but have had no complaints when used in smaller engines.

 

[Don S]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

Here is what you get if you order from Mercruiser.
This is from the 2012 Accessory guide

View attachment 2012 MC spark plug chart.pdf

Personally, I don't care which plug is used if it works. Too many problems with Champion, so they are out (NOTE: Champion is all that Volvo Penta sells). NGK I have never had problems with, but was able to get so,, that is why we used them.
Never looked for nor found a conversion chart for the other types of plugs. Had no need to.

 

[Tail_Gunner]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

Some thing's never seem to change as far back as i can remeber champion's were a dirty word, if i remeber right they would foul or short out all the time. This much i know the part's man who stocked the parts would get his A@# chewed when the old man caught him stuffing the plug bin with champ's..:laugh:

 

[tpenfield]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

Here is what you get if you order from Mercruiser.
This is from the 2012 Accessory guide

View attachment 180294

Personally, I don't care which plug is used if it works. Too many problems with Champion, so they are out (NOTE: Champion is all that Volvo Penta sells). NGK I have never had problems with, but was able to get so,, that is why we used them.
Never looked for nor found a conversion chart for the other types of plugs. Had no need to.

Yea, looks like my engine's plug maps to the AC-Delco MR43T . . . So, I'll go with that. I see that many of the engines map to the NGK brand.

 

[Don S]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

Yea, looks like my engine's plug maps to the AC-Delco MR43T . . . So, I'll go with that. I see that many of the engines map to the NGK brand.

It's just an alternative, your service manual will list the AC, NGK, and Champion numbers. But nothing wrong with going with the AC, GM liked them and they work very well.

 

[Fun Times]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

He mentioned that in his experience, the GM-based engines seem to run best on the AC Delco brand of spark plugs, and recommended those versus Champion or NGK.

In the past i'v used NGK A lot due to ease of accessibility plus the fact that mercruiser recommended them for a long period of time and sent them out to dealers in place of AC delco. Since that time mercruiser has now started offering both AC delco & NGK plugs as a choice. But on some part numbers that used to be NGK have now superceded back to AC-delco, For example, 33-898264001 AC SPRK PLUG has superceded from 33-59571 NGK SPRK PLUG.

I can recall on two separate occasions the service shop i worked for had a prop shaft dyno, after running the big block engines up to see what kind of power they were producing, we then immediately switched out one set of AC-delco on one boat and one set of champions on the other boat and we gained almost 100 PSI of power on the power gauge on both boats. Now to be fair, i'm not sure if it was because of having new plugs in general or if NGK's are just better.

The only issues i'v seemed to really noticed over time when using the NGK's is that on some engines they seem to have an tendency to collect carbon faster then the AC delco plugs, especially on the 500 EFI's. The NGK's electrode gets a heavy build up of carbon around the base which could eventually cause a lack of power, rough idle, detonation, etc. So you may want to keep an eye out for those issues.

 

[RogersJetboat454]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

Lol!!
Although I'd normally agree...I'm willing to bet that if I just walked around my "neighborhood" and pulled the ignition wire off the mowers/blowers/tillers/tractors and weed whackers I'd find the dreaded "C" word written on 90% of the plugs!

I'm not a big fan of them in anything with more than two cylinders, but have had no complaints when used in smaller engines.

IMHO it all comes down to what make of plug the engineers designed the engine around. The majority of small engines were designed to use Champions as their go-to plug. I use them my self in my Briggs or Tecumseh engines, and they work fine. All those engines usually have ignition systems that make 15Kv or less.

You put the C word in a modern anything with a high output ignition, and it seems all bets are off.
I can't count how many people who came to me after getting the "tune-up special" at some grease pit shop, and their car is now throwing misfire codes. 90% of the time it's a Champion plug I pull out, with some nice carbon tracking down the side. The other 10% is a Bosch installed in something other than a Chrysler, or European car.

 

[MWG2600]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

ngk makes delco plugs.....

 

[tpenfield]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

ngk makes delco plugs.....

I have seen comments to that effect on some automotive forums . . . I wonder if it is just some types or accross the board. I have also seen comments about some AC Delco plugs being made in Mexico..

I guess the only things made in the USA any more are cheeseburgers and fries. :noidea:

I'll go with the AC-Delco, regardless of where they originate. I'm sure NGK would probably be fine also.

 

[Don S]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

It wouldn't surprise me if NGK actually manufactured some or even all of the AC plugs simply because they have the factory, but like anything else, it's made to AC specs, including material specs.

Again, just because you can read or hear something on the internet, sure doesn't make it true.

 

[MarkSee]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

I guess the only things made in the USA any more are cheeseburgers and fries....

...I'm going with only ASSEMBLED in the USA......parts of the cb and fries combo obtained from ?????

Mark

 

[tpenfield]

Re: Spark Plug Choice - Mercruiser 7.4 LX MPI

A quick update on the spark plugs:

I replaced the spark plugs on the engines today . . . the old ones were Champion brand and it appears that they were not marine rated plugs

Here is a picture of the old Champion versus the new AC Delco



the Champions were RV15YC4 and it looks like they are hotter running plugs than the AC Delco MR43T that I am putting in there. I noticed that the plug electrode extended about 1/8" further into the cylinder chamber than the AC Delco's.

Here is the entire set from the Starboard engine . . .



Lots of rust . . . they are black in appearance mostly because of the MPI fogging that I did in the Fall . . . still a nice oily coating on them from the fogging.

anyway, I'm glad to see these plugs going in the trash.