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Author Topic:   Inductive Resistor Spark Plugs
newt posted 06-19-2003 12:56 PM ET (US)   Profile for newt   Send Email to newt  
The manual calls for using NGK BUZHW2 spark plugs in my 2003 Mercury 90 classic (2s). The NGK website lists BUHW2 as the correct plug up to and including year 2000 for this motor. The difference is only one letter "Z", which indicates 'Inductive Resistor' according to the link below.

According to the info here, , The benefit of the resistor plug is to avoid interference with electronic equipment.

The difference in cost is about $7/plug. I have two questions:

1. Do the 2003 Mercury Classics vary much from the previous years?

2. Is anyone using the non-resistor plugs in this model engine with satisfactory results?

The BUHW plugs are readily available, and I wonder if they would work OK in a pinch.

Matthew posted 06-19-2003 01:38 PM ET (US)     Profile for Matthew  Send Email to Matthew     

My outboard is a 2002 Mercury 90 2 stroke and
I recently replaced my plugs and used the factory recommended "BUZHW2". The Mercury dealer had never heard of that model # spark plug and had to special order a box, leading me to believe that the plugs are fairly new.

He originally gave me the BUHW2's when I told him the make and model of my engine. But I noticed the difference when removing the old plugs.


jimh posted 06-20-2003 09:42 PM ET (US)     Profile for jimh  Send Email to jimh     
The NGK resistor plugs are quite expensive and hard to find. Use of resistor plugs is probably intended to keep radio interference suppressed, but it also could have an slight effect on the ignition circuit.

The use of the letter "Z" is interesting. Z is often used in electrical circuits to represent complex impedances, circuits which contain both resistive elements and reactive elements. By winding the resistance material into a small coil, NGK also creates and inductive reactance that helps their plug to suppress the generation of radio frequencies. I always thought it was a good letter to use, instead of just an R for example.

Changing to resistive plugs in the 2003 model might just be part of Mercury's on-going effort to produce a better product and make improvements to their engines. Perhaps it was a reaction to complaints of too much radio interference.

I would get the recommended plug. I am sure you can also get a set of non-resistive plugs for a spare, too.

Dick posted 06-20-2003 10:11 PM ET (US)     Profile for Dick  Send Email to Dick     
In my experience motor manufacturers care more about plug interference with the motors electronics than radios, etc.

I agree with jimh use the plugs recommended by Mercury and no other. They are using that plug for a reason.

I stock both plugs but can't pull a price out of my head, I'll check them on Monday. There is a tremendous mark up on spark plugs if sold at the MSRP, some dealers will discount down to a fair mark up.


newt posted 06-20-2003 10:43 PM ET (US)     Profile for newt  Send Email to newt     
I agree that you won't go wrong using the manufacturer's recommended plug, however I hate to throw away the 6 clean non-resistor plugs that I have. I may as well use them as spares. I still wonder what is different between the 2003 engine model and previous years that would neccesitate the plug change.

Any Mercury experts care to comment?

jimh posted 06-22-2003 11:15 AM ET (US)     Profile for jimh  Send Email to jimh     
Dick--That is an excellent point. Suppression of interference from the plug firing may be important to getting the electronics inside the engine to work properly.

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