What sparkplug on Mercruiser!? Help!

Joined
Jun 20, 2012
Messages
8
Hi everybody!

I was about to change the sparkplug on my Rinker Captiva 232 with Mercruiser 5.0 engine.

On the airfilterbox it tells me to use the AC-MR43LTS Sparkplug and when i cross-reference it to NGK it want me to use NGK BPR6EFS.
But when i start to change the sparkplug i see that the plugs mounted in the engine is NGK BR6FS, an sparkplug much shorter then BPR6EFS iam getting really concerned so i dont put to long sparkplugs so the engine will fail.

Please help me with this, i attach pictures on the airfilterbox with engine serialnumer and picture of the sparkplugs.
How will i know for sure what sparkplug i should use?

bild-10.jpgbild-11.jpg

Thanks guys.:)
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
17,624
Re: What sparkplug on Mercruiser!? Help!

I have those NGK plugs in my 7.4L Merc . . . I too would be apprehensive about using the longer ones.

I would check the engine serial number on the block and cross reference it on one of the mercruiser parts sites,

Www.mercruiserparts.com or www.perfprotech.com

You will find the engine serial number on a plate right above the starter . . . Check to see if it matches the numbers on the air intake cover. Then, see what the reference sites have to say about the correct spark plug


You can also use a paper clip to 'feel' the depth of the threads to see which of the two plugs they seem to match.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: What sparkplug on Mercruiser!? Help!

What's the serial number of your engine?

NGK BPR6EFS are the correct equivalent for AC-MR43LTS... It's entirely possible that some meat-head has put the wrong plugs in... :facepalm: Or put a newer model cover on the engine.... But a serial number will sort that out... Best get the serial number off the aluminuim tag above the starter motor than the cover... ;)

Chris.......
 

markheck1

Petty Officer 2nd Class
Joined
Mar 31, 2012
Messages
124
Re: What sparkplug on Mercruiser!? Help!

I'm guessing you have vortec heads, which seem to use the 18mm reach plugs.....
if everything is original, and you are sure about the "L" because that is the 18mm reach,
then it should be the long ones,
I would still look it up as stated above just to double check.

ETA..OH! and NEVER go by what was in it before......I see wrong spark plugs in power equipment every day....usually on things coming into the shop...go figure.....
 

TilliamWe

Banned
Joined
Dec 21, 2004
Messages
6,579
Re: What sparkplug on Mercruiser!? Help!

Hi everybody!

I was about to change the sparkplug on my Rinker Captiva 232 with Mercruiser 5.0 engine.

AC-MR43LTS Sparkplug and when i cross-reference it to NGK it want me to use NGK BPR6EFS.
But when i start to change the sparkplug i see that the plugs mounted in the engine is NGK BR6FS,

View attachment 153430View attachment 153431



Thanks guys.:)

If your engine has Vortec Heads, the MR43LTS is the correct plug. And if your engine has Vortec Heads, that dirty plug in your right hand is WRONG. That's the cross reference to a MR-43T, which is the plug for a non Vortec engine. If your engine has Vortec Heads, the longer plug is correct.
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: What sparkplug on Mercruiser!? Help!

The serial number shown on the flame arrestor shows you should have Merc part number which is 33-816336, which if you ordered from Mercruiser you would receive the NGK BPR6EFS. The AC MR43LTS is the OEM plug from GM.

The reason you have the short plugs in there is because the last person doing the plugs didn't know what he was doing.
 
Joined
Jun 20, 2012
Messages
8
Re: What sparkplug on Mercruiser!? Help!

Thanks for all the answers, as you can see on the picture the serial number is "0L090832" and it matches the serialnumber on the engineblock.

Everything points that its BPR6EFS that should be in the engine, but it have been running fine with BR6FS that is my main concern.


How do i know if i have Vortec? How can i check that?



Thanks again! Hope we can sort this one out :)
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: What sparkplug on Mercruiser!? Help!

How do i know if i have Vortec? How can i check that?

It will run better with the correct plugs in it, as far as ID of the heads, it's not really necessary. Just look at the spark plug holes, and see if the threads are long like the BPR6EFS spark plug.
 
Joined
Jun 20, 2012
Messages
8
Re: What sparkplug on Mercruiser!? Help!

It will run better with the correct plugs in it, as far as ID of the heads, it's not really necessary. Just look at the spark plug holes, and see if the threads are long like the BPR6EFS spark plug.


Still a littlebit nervous about this.
? have tried to see/feel the threads, but its not possible where they are located.
I would like to know to look after something specific that really confirm the plugs before i change them.

Thanks for the help.
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: What sparkplug on Mercruiser!? Help!

My information came from the OEM service manual, and the OEM Dealers parts program. Plus I told you to look at the plug holes and how long the threads are in the head. On your model number and serial number the short ones were NEVER used.

Be nervous if you want, but you need the long plugs.
 
Joined
Jun 20, 2012
Messages
8
Re: What sparkplug on Mercruiser!? Help!

My information came from the OEM service manual, and the OEM Dealers parts program. Plus I told you to look at the plug holes and how long the threads are in the head. On your model number and serial number the short ones were NEVER used.

Be nervous if you want, but you need the long plugs.


Thank you for the help.
The gap should be set at 0.045 ( 1.13mm ) but iam limited to set it to 1,1 mm ( 0.044 ) will that be ok?
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: What sparkplug on Mercruiser!? Help!

.044 will be fine, just make it a slightly loose .044.
 

TilliamWe

Banned
Joined
Dec 21, 2004
Messages
6,579
Re: What sparkplug on Mercruiser!? Help!

Be nervous if you want, but you need the long plugs.

Yes, he's EXACTLY right.

But if you really want to ID Vortec heads, just look at and count the intake manifold bolts. There will be only 8 total, and they are straight up and down. All other heads have 12 and the bolts are at angles. Easy.
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
17,624
Re: What sparkplug on Mercruiser!? Help!

If this is an older boat, I would still want to get some sort of visual verification that the heads take an 18 MM deep thread.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,468
Re: What sparkplug on Mercruiser!? Help!

If this is an older boat, I would still want to get some sort of visual verification that the heads take an 18 MM deep thread.

Ayuh,.... It Ain't hard to tell.....

If the head has 4 intake bolt holes,.... It's a Vortec, 'n uses the long plugs....

If it's got 6 intake bolt holes,... It takes the MR43T plugs...
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: What sparkplug on Mercruiser!? Help!

If this is an older boat, I would still want to get some sort of visual verification that the heads take an 18 MM deep thread.

That is exactly why I told him to LOOK at the threads to be sure. Sometimes people need to get off their butts and physically look or do something instead of looking for some magic button online so they don't have to do anything but type on their keyboards.
 
Joined
Jun 20, 2012
Messages
8
Re: What sparkplug on Mercruiser!? Help!

I would like to thank everyone that replied in this thread!

I have now changed all sparkplugs to BPR6EFS and measured the sparkplugseat also looked at the intake and it was Vortec.

It now starts and run much smoother, thank you all!
 

sethjon

Senior Chief Petty Officer
Joined
Jun 8, 2010
Messages
692
Re: What sparkplug on Mercruiser!? Help!

Still a littlebit nervous about this.
? have tried to see/feel the threads, but its not possible where they are located.
I would like to know to look after something specific that really confirm the plugs before i change them.

Thanks for the help.

Hear this! I only agree 99.9% of the time with Don S. and having said that in this case he is spot on. Listen to his answer.
 
Top