Another: Which Spark Plug Thread

[jeepnsam]

1995 Searay
Merc 5.0 v8 305 CID
Alpha I Gen II

The owners manual says to use:

AC-MR43T
Champion RV8C

The air cleaner cover says to use:

AC-MR44T

I pulled out:

Champion RV8C

When I pulled one out:

* ceramic insulator broke in half
* electrode was black and sooty looking

I've read the AC-MR43T is the cold plug and the AC-MR44T is the hotter plug.

Which one would you recommend based on the above analysis??

Thanks,
Sam

 

[Bondo]

Re: Another: Which Spark Plug Thread

Which one would you recommend based on the above analysis??

Ayuh,... The AC Delco MR43T,.... Then fix the Carb...

 

[jeepnsam]

Re: Another: Which Spark Plug Thread

> The owners manual says to use:
>
> AC-MR43T
> Champion RV8C
>
> I pulled out:
>
> Champion RV8C

I did a cross reference and the RV8C is not a Marine Rated plug so why would the manufacturer suggest a non-marine plug as an alternate to the MR43T??

An why would the air cleaner cover state to use the MR44T which is the hotter plug??

I'm thinking the owners manual is the "best practice" guide and the Air Cleaner is the "use this one" guide? What's your opinion?

YES the carb seams a bit rich, so I'll have that taken car of also...just want to get the correct plugs in there since the RV8C's I pulled out crumbled.

Thanks,
Sam

 

[JustJason]

Re: Another: Which Spark Plug Thread

I'm thinking the owners manual is the "best practice" guide and the Air Cleaner is the "use this one" guide? What's your opinion?

Actually the best practice is to follow....
1. The Dealer parts listing and/or any TSB's regarding that motor.
2. The factory service manual

Unless your the original owner it may not have the correct plastic up top.

Pretty much universally, those motors all run AC MR43T's. They also will run an NGK equivelent. If you ask most mechanics they will tell you champions are lousy. I'm a mechanic and i'll tell you champions are lousy.

You'd only want to run MR44s in that motor if you were running in cold weather all the time in a lightly loaded boat.

 

[zbnutcase]

Re: Another: Which Spark Plug Thread

Champions are lousy! NGK is what I use.

 

[jeepnsam]

Re: Another: Which Spark Plug Thread

More information for the Forums:

The higher the number, the hotter the plug on AC Delco Plugs:

M = marine
R = resistor
4 = 14mm thread
3 = heat range
T = tapered seat shell design

However the cross references are not always in the same heat range
as the manufactures recommended plugs (MR43T).

http://www.sparkplugs.com/results_cross.asp?pid=MR43T&x=0&y=0&seenCrossWarning=1

CONCLUSION:

I'll stick with AC MR43T's.

Thanks,
Sam

 

[JustJason]

Re: Another: Which Spark Plug Thread

Wise choice!

 

[jeepnsam]

Re: Another: Which Spark Plug Thread

UPDATE:

> The owners manual says to use:
>
> AC-MR43T
> Champion RV8C
>
> I pulled out:
>
> Champion RV8C

Now here's the comparison between a new AC-MR43T picked up from NAPA today and the old broken Champion RV8C. What a major difference in length.

Blurry Pic
http://i133.photobucket.com/albums/q75/jeep_n_sam/IMAG0083.jpg

 

[Don S]

Re: Another: Which Spark Plug Thread

Here is from the OEM service manual The blue dotted line indicates a change from a parts bulletin.

 

[gjcombs]

Re: Another: Which Spark Plug Thread

moved to new thread....