1998 Mercury 225 EFI correct gas???

[wjhuskey]

I have a 1998 Mercury 225 EFI on my Ranger Comanche. It has never missed a beat until the last time out. It fired up great as usual and it idled for probably 5 minutes. It wouldn't start when I got back to the dock from parking my truck. I'm a farmer and I have one of the best mechanics on earth (that's why I hired him)...he is great with boat motors as well. He said it was probably bad gas. The spark plugs were black when we pulled them out. He done some research and found out that only premium gas needs to be ran in this motor because of the octane rating that the engine needs. I always tried to get ethanol free gas to avoid using the treatment and would sometimes have access to it near the lake...so it has had premium put in it but not the last couple fill ups. I will only run premium gas from now on because the motor wasn't even burning the oil good with the regular unleaded. I'm learning this boat stuff one mistake at a time. Anyways, just wanted to ask if it possibly damaged the engine any running the wrong gas?...and wanted to hear from you guys about what gas your running in your 225 EFI in this age range.

[SilverFox579]

Try posting in the 3L forum (what your engine is) and be sure to include your engine serial number. There's a great FAQ at the top of the 3L forum that addresses your fuel question - Oil, Battery, Spark Plugs, Fuel and Fuel Additive Recommendations

From the linked topic:

FUEL:
-All models- MAXIMUM ETHANOL CONTENT: 10%. Ethanol content may adversly affect engine performance.
-See "Mercury's View of Ethanol" on Sherm's board at: http://www.bbcboards.net/mercury-mot...nded-fuel.html
-Standard Opti's (ALL) 87 Octane MINIMUM.
-Standard 2-stroke Carb/EFI Models: 87 Octane MINIMUM.
-XS, XB or Racing PRIOR to 2006- CONSULT OWNER'S MANUAL! Most require High-Test!
-ProXS and 250XS 2006-UP: 87 Octane MINIMUM. IF poor idle quality occurs, could can try 89 Octane (mid-grade) to see if quality improves.
-300XS- Consult Owner's Manual. High Grade (minimum 91 Octane) fuel required!

Unless your engine is a racing version or has been modified in some way to require premium, you should be using 87.

[mdtritn21]

98 225 efi 87 octane not premium and the right plugs QL77CC only.

[leonreno]

How long had it been since the plugs were changed? Right gas or not, plugs turn black if when used longer than they should be. Use a good fuel additive like Quickleen to reduced carbon deposits. Quickeleen is probably cheaper than premium fuel.

[EuropeanAM]

And "Premium Fuel" would be doing exactly the opposite of "reducing carbon".

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