98 merc opti 135

[justin99]

looking to replace spark plugs today, found three different model number of plugs in the merc book. What is the consensus on here as to which is best to run??

[JDP]

justin99,

I have a '98 150 Optimax. Over the years Mercury has changed the recommended spark plug at least once I believe.
Given the cost of the plugs $14-$20 depending upon where purchased I call:

Mercury Customer Service (920) 929-5040

whenever I am about to purchase spark plugs to ensure I get the correct plugs. Last year I bought my plugs from Advance Auto Parts by placing an order on-line and picking them up at the store.
I have found these folks to be very helpful to me over the years.
If you call them have you Opti's model number and serial number on hand in case they ask.

In the past I have purchased them also at NAPA Auto Parts. You will save $30 or so by checking pricing.

[staylor]

My 2002 Opti 150 has had 3 different plugs listed over the years. The latest is the NGK 1ZFR5G which is an Iridium plug- and quite expensive. It does run the best of the 3 plugs listed, especially when trolling. If this is one of the plugs they list for your 1998 model, then this would be the latest type. These plugs come with a narrow gap of .03 and the extremely fine- and brittle- Iridium center electrode. They should be run with either the .03 gap out of the box, or if you are adept with feeler gages and ONLY bend the outer electrode very carefully you can get a bit better trolling with the gap opened to .032-.033 by using a .032 feeler gage stack as "go" and a .033 stack as "no go". Be extremely careful when checking the "no go"- since the center wire electrode is about as brittle as glass. The Iridium plug gap will not change over time until you've got many hours on the plugs- I suspect 100 hours plus.
Doug