225 EFI spark plug question

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TightlineT

Active member
I have a 2003 Mercury 225hp EFI that I am changing plugs on. Old plugs are champion ql77cc and that seems to be correct plug from what I have found online. My problem is some sites are showing a .035" gap and some are showing .040". Anyone out there have any experience with which one is correct? Thanks in advance.......Jim
 
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TightlineT

Active member
Thanks for the info. I think that's what has led to the confusion......I saw that and then appears to be .035 on the marineengine.com website for Mercury. Guess I could go with 40 and if it don't run good try the 35. Thanks again
 
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rodman55

Member
I have the same motor. My SN is 0t674533 2003 225 EFI. After hours of research and talking with Mercury pro staff. the Champ plugs are gaped at 35. NKG plugs are gaped at 40. I've been doing this for 15 years now every spring and have had no problems. with plugs or firing. I have noticed a slight increase in RPM with the Champ plugs gaped @ 0.35. good luck and Great question.
 
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TightlineT

Active member
rodman55 - 2/22/2019 7:12 AM

I have the same motor. My SN is 0t674533 2003 225 EFI. After hours of research and talking with Mercury pro staff. the Champ plugs are gaped at 35. NKG plugs are gaped at 40. I've been doing this for 15 years now every spring and have had no problems. with plugs or firing. I have noticed a slight increase in RPM with the Champ plugs gaped @ 0.35. good luck and Great question.
Click to expand...

Wow! My SN is within 5 at 0T674528. Thanks to all for the info......Jim
 
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rodman55

Member
They burn hotter, that's why the .40 gap, champions are a colder plug and with .35 you are not pushing your coils as hard to fire. a .40 seems small buy it don't take much to overheat and break down a coil. I do run the NKG is the colder months then go back to the Champions when water temps it 70. I fish Woods ,Tim's ford and Tennessee river and have never had a break down or engine trouble. I would also say that when changing out the plugs use the grease for plug wires and the thread protector on the threads. Its also a good time to make sure the lower unit oil is Drained, Flushed, and refilled. If its been longer than 3years i will replace water pump impeller too.
 
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silvertalon

Active member
Mercury recommends NGK plugs in All of their outboard product. OMC rec'd Champion. Both will work just fine with either or. It's kind of like- GMC rec'd AC Delco etc. However, stay with NGK in Optimax motors. Tech tips I can give- eg; When the gap is .040, set the gap .002 less- .038. This is because when a plug gets hot, the gap will expand about .002. Also, If you are running an oil injected motor that has the injection disabled (pre-mixing oil and gas), go one step hotter with your plugs. This will help burn off the extra oil and reduce carbon build-up, sticky rings and plug fouling. In fact, OMC service school recommends this regardless of oil injection eg; QL77JC4, go to a QL78C. NGK temp range numbers are opposite eg; BU8H, go to BU7H (lower number is hotter).
 
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