Optimax 135HP

[wkwarrior]

i am looking at a boat with 98 optimax 135hp engine. the engine has a knock at idle and goes away or can't hear it when it is running. for all the experts our there

- does this sound like a piston pin wear?
- is the optimax 2.5L block the same as other mercury 2.5L block?
- hear about an injector upgrade that needs to be done to this engine for added reliabilty?
- where can i buy the software if it exist (my laptop) to scan ECU?

thank you

[sosmerc]

You need the DDT to Scan your 1998 Optimax, though I hear the new Merc CDS system will eventually "communicate" with the older DFI product.
All the 2.5 litre DFI (Optimax) powerheads are rather noisey in my opinion. I own a 1998 135 Optimax myself, and while the engine runs fine, I sure don't like some of the sounds it emits at certain rpm's. I am hoping Merc addresses this with the "next generation" Optimax engines that are now out. (I am rigging a new 2.5 litre 175 Optimax this week...so I will soon know if they have made any significant changes to the 2.5. It sure doesn't look any different under the cowl than least year's model...so I don't know....maybe the "real" changes were done to the 3.0 litre Optimax engines :)))

[wkwarrior]

sosmerc,

how many hours on your engine? any problems since? thanks

[sosmerc]

My engine has about 160 hours on it. I get an occasional warning horn and light and my DDT says it"s a faulty TPI. But I think it is caused by slop in the control cables, such that the TPI (s) do not always return to the exact position at idle so their voltage output signal is not what the ECM expects to see...and it trips a code. If I shift into reverse, and then back into neutral, shut the engine off, and then restart...all is then ok.
The engine often runs rough at idle when cold, but later runs fine when fully warmed up. This can be alarming and frustrating, especially when it's your own personal boat and you make your living working on these damn things...but I am hoping to upgrade to a next generation Optimax motor before too long. I still would rather have an Optimax than a 4 stroke at this time. Fuel economy and performance are excellent.

[staylor]

...2002 Opti 150. The engine idles better than any 2 stroke I've ever owned at all times, even with water temp at 32 and air temp in the 20s. In gear idle speed is 550- 570 rpm on the smartcraft display.The only noise I've noted is a bit of a growl at 3000 rpm, but I'm pretty sure it's just the intake passing thru a resonant point. I have no noise that resembles a knocking at any speed. Total hours shown on hour meter is 110. The only service issue I've had is that the plug type has been changed 3 times- each successive change has run even smoother, but at a higher cost for the plug. One stray thought on the knocking you've noticed is the belt tensioner pulley. This is on the top of the block on the port side under the plastic air intake cover. There is a grease fitting on this pulley that most owners aren't aware of- it's well hidden and noted in the manual- but you have to read the manual closely to see it listed. You might idle the engine after greasing this and giving the pulley itself a quick shot of WD-40 to see if this changes the knocking- indicating a bad tensioner or a worn belt.
Doug

[M.CHAPMAN]

The chugging of the air compressor has sounded like a knock to some folks. The opti's will sound different when idling. There were sevearl recalls on the optimax over the years. You can have a Dealer check on Mercnet to see the claim history on it and make sure all upgrades have been made.

sosmerc,
As for the TPI faults, you are probably correct on the linkage being at fault. The linkage should be adjusted to where the roller on the throttle shaft does not touch the cam when you return it all the way to idle. Make sure also there is not to much preload on the cable at the stop. This can put pressure on the TPI linkage and cause the arm to move just enough to signal a fault. Been there done that!!!!!
-Michael

[wkwarrior]

thanks for the feedback. there are 2 engine on the boat, unfortunately only one makes this knocking sound. also, do i expect better than 50:1 oil use on this engines?