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Thread: 2.5 EFI questions.

  1. #1
    I'm still searching for a semi-accurate answer to the lifelong question "How long do the Mercury 2.5 EFI's hold up before dropping a locating pin and scorching the motor?" Are there certain years which are better than others? I've heard that the Wiseco pistons that these motors came with during certain years are terrible. Is this correct? Any ideas as to what years they used Wiseco's / ART's / Mahle's?
    Any insight that you can give is greatly appreciated.

  2. #2
    Unloaded Racing
    I got a 93 2.5 245 carb that has been run to death. put rings and bearings in it, Raced it 2 years and still has good leak down. This motor has Mahle's in it. I have seen guys put Wiseco's in and not get the motor broke in before it ate a piston, I have also seen the Wiseco's last. Wiseco was suppose to have went to a top locator pin to eliminate failure. I do not know if they did or not. I know most everybody that races use something other than Wiseco.

  3. #3
    ypu are correct these pistons are terrile i would expect about no mer than 3 years of hard running i suggest a 1996 model

  4. #4
    Are the 1997's 2.5 EFI's any better?

  5. #5
    My experience with 2.5s is that if you keep them in the standard running range (less than 7600) they'll last quite a while. The guys who have the most problems are those who have the rev limiters removed and are running over 8000 rpms.
    I never had piston problems until I ran my drag motor. At 10000 rpms, I had to put 3 sets of pistons in in one year.
    The best piston (in my opinion) is the new drag piston. Single ring, top stake piston. The pin can't come out.
    The later style (I want to say they started in 1999 or 2000) 280 piston has the top stake as well but is a dual ring piston. Any of the top pin location pistons (only ones you can get now) will last just fine.
    Sam Baker
    Baker Marine Support

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