Merc Standard Spark Plugs

[gjcombs]

All,

I have found that this is a fairly common discrepancy. I too just pulled my plugs out of my 1994 Mercruiser 5.0LX (Thunderbolt IV) engine to find that they were MR44T and not MR43T. The service manual and my owner's manual call for MR43T.

Here's a similar thread
http://forums.iboats.com/showthread.php?t=408631

A side note, the Seloc manual has RV15Y which is not RV8C that is the alternate in the owner's manual. This was for the 5.0LX. For just the 5.0L, they listed the RV8C.

I will stay will the MR43T, but would like to understand more:

1. Per the Seloc manual, why would they call for something different for an LX?

2. Why is this a common occurrence?

2. Has Mercury issued a change bulletin to go from MR44T to MR43T? Why?

3. What would be the performance difference between the two?

4. What does a "hotter" plug mean?
__________________

 

[Bluestream]

Re: Merc Standard Spark Plugs

The temperature of the spark is hotter; less likey to foul

 

[mkast]

Re: Merc Standard Spark Plugs

http://www.ngk.com/charglossary.asp?kw=Heat+range

 

[sethjon]

Re: Merc Standard Spark Plugs

All,

I have found that this is a fairly common discrepancy. I too just pulled my plugs out of my 1994 Mercruiser 5.0LX (Thunderbolt IV) engine to find that they were MR44T and not MR43T. The service manual and my owner's manual call for MR43T.

Here's a similar thread
http://forums.iboats.com/showthread.php?t=408631

A side note, the Seloc manual has RV15Y which is not RV8C that is the alternate in the owner's manual. This was for the 5.0LX. For just the 5.0L, they listed the RV8C.

I will stay will the MR43T, but would like to understand more:

1. Per the Seloc manual, why would they call for something different for an LX?

2. Why is this a common occurrence?

2. Has Mercury issued a change bulletin to go from MR44T to MR43T? Why?

3. What would be the performance difference between the two?

4. What does a "hotter" plug mean?
__________________

One's slightly hotter. Stick with the 43's.

 

[Aloysius]

Re: Merc Standard Spark Plugs

The temperature of the spark is hotter; less likey to foul

No..the spark is the same. however, the operating temperature of the plug is hotter..the insulator and electrode.

The temp difference between a 43 (cooler) and a 44 (hotter) is slight. go for the 43..less likely to cause preignition under severe conditions.

 

[Don S]

Re: Merc Standard Spark Plugs

A side note, the Seloc manual has RV15Y which is not RV8C that is the alternate in the owner's manual. This was for the 5.0LX. For just the 5.0L, they listed the RV8C.

1. Per the Seloc manual, why would they call for something different for an LX?

2. Why is this a common occurrence?

2. Has Mercury issued a change bulletin to go from MR44T to MR43T? Why?

I guess the first thing you need to understand is that Seloc is an aftermarket manual, many times wrong, and having their own ideas about things.
Seloc, not Mercruiser, changed the plug types. Merc uses the same plugs on the 5.0L and the 5.0LX.

If you go buy a Seloc and a Clymers manual, you will have a knee pad for both knees while working on your boat, while reading your OEM service manual for accurate information.

 

[gjcombs]

Re: Merc Standard Spark Plugs

Har-de-har and understood. I typically don't use that manual since I have the Merc ones, but was just a check.

I saw on the spark arrestor hood that it also calls for MR44T. I am still going with MR43T as listed in the more current Merc Manual. However, I am curious as to why Merc is different.

As if Merc were saying, "we use MR43T plugs in all of our other engines, BUT ON THIS ENGINE, we are using MR44T...".

 

[Aloysius]

Re: Merc Standard Spark Plugs

Carbureted engines tend to run leaner on ethanol laced fuel..leaner can create a hotter condition in the cylinder, and would benefit from a slightly cooler plug.

 

[gjcombs]

Re: Merc Standard Spark Plugs

Carbureted engines tend to run leaner on ethanol laced fuel..leaner can create a hotter condition in the cylinder, and would benefit from a slightly cooler plug.

An excellent reason to go cooler!

 

[Bluestream]

Re: Merc Standard Spark Plugs

No..the spark is the same. however, the operating temperature of the plug is hotter..the insulator and electrode.

The temp difference between a 43 (cooler) and a 44 (hotter) is slight. go for the 43..less likely to cause preignition under severe conditions.

Correct, meant to say tip not spark. Use NGK at any rate...