Whaler Central - Boston Whaler Boat Information and Photos

Posted by deajam89 on 08/12/19 - 12:55 PM

I recently had a 2019 Mercury 90hp installed on my 2000 Montauk 17 and have experienced some questionable engine issues that i though i would bring to the forum. The motor is "shuddering" as if it were low on fuel after 1 - 2 weeks of sitting at the marina. The shuddering is not consistent and varies from a non-noticeable slight shake to more prevalent shudder/shake. Over the past few months, i would top off the external gas tank with fresh 89 and run the boat at WOT for a few minutes and the issue would go away as advised by the certified mercury marine mechanic.

I first experienced this issue when i connected my second external gas tank which had about 1" of Oct 89 fuel from the previous season. i topped of this 6 gal tank with about 5.75 gal of fresh 89 oct fuel from the marina and hooked it up to the fuel line. Soon there after the motor started shuddering as if it were starved of fuel. I brought the boat back to the marina where the repower was done and explained the situation. He explained that the fresh gas immediately separated the residual moisture from the old gas and water was blocking the fuel filters. He told me to top off the fuel tanks and run the motor and see if the issue went away before i bring it in (which it did). Since i was at the 18 hr mark, we did the 20hr service and changed the fuel filters. He assured me that even if it was a little bit of water, there is no concern with damaging the motor.

This issue returns almost every time the motor sits over the week during the first hour or so of low RPM operation. The vesselview has not shown any faults during any of these events. And like i said, it goes away with fresh gas and WOT for a few minutes.

Any thoughts on this? I cant believe that a little water (if it is water) would affect this motor so much... Needless to say it is a little disappointing.

Posted by Phil T on 08/12/19 - 1:23 PM

Modern EFI motors are sensitive to fuel quality.

You can't run on old fuel unless it has been treated with a fuel stabilizer when purchased.

By adding fresh fuel to the old fuel, you have most likely contaminated all the fuel in the tank.

The wisest action is to dispose of the contaminated fuel properly. Expect to pay several dollars per gallon. Do not use it in your vehicle. You might in a 2 stroke mower, weed trimmer, chain saw etc.

With fresh fuel the engine will still idle rough until the contaminated fuel is run through all the hoses, low and high pressure fuel pumps, high pressure fuel rail and the VST.

You should treat every gallon of fuel at the station/dock with fuel stabilizer product to prevent this problem in the future.

Edited by Phil T on 08/12/19 - 1:28 PM

Posted by MG56 on 08/14/19 - 3:25 PM

Well, I think adding good gas to bad gas is not helping anything. You still have bad gas.

You have a new engine but do you have new fittings and gas lines? I doubt this has anything to do with it from the way you explained the problem but at least put this on the list of possible problems.

This one is out there but how good are your battery and cables? The clue for this one is you said "after a week of sitting" you run WOT and then things are fine. All of a sudden bad gas or gasline defects are ok? No, that doesn't really add up.

And not for nothing but how do you like that new Merc? We hear all about eTec 90s and Yam 70s but I can't remember someone with a new Mercury talking about how they run.

Posted by deajam89 on 08/16/19 - 8:07 AM

Thank you guys for the reply.

Do you recommend a particular fuel stabilizer product?

Another thought is i leave the vents on the gas caps open all the time... I do this to avoid the tanks from over expanding and rupturing... They are under the seat but by no means isolated from rainfall.

Everything except for the steering wheel was replaced during the re-power. I will check but i would imagine that all the battery cables are firmly attached and the battery is brand new.

Another issue, I hear a high pitched "slight coffee grinder/crazy harmonization" type sound when I am at exactly 1400 rpm. When i bring the boat up to speed slowly and reach 1400 rmp, the sound is rather pronounced over the extremely quiet operating noise. This sound subsides once i throttle beyond 1450 rpm. Similarly, when i am running +4000 rpm and bring the throttle down slowly to pass 1400 rpm, the noise returns until I reach around 1300 rpm. Often I will be operating around 2500 - 3000 rpm and quickly throttle down to idle. When i do this, the noise almost is non-existent.

This phenomena was explained to me as "gear case harmonizing" which is common in outboard motors and can be heard so prominently due to the low operating noise of the new 4 stroke motors.

Any thoughts on this?

As for the Mercury 90, I am extremely happy with the purchase. I often question if the Yamaha 70 would have been a better idea for my needs but i am happy that i went with the 90. see below for Pros and Cons.

Pros:
-NO 2 STROKE OIL TO CHECK AND FILL!
-Extremely quiet (especially at idle speed)
-Smooth gear shifting
-Quick and immediate start up
-More sturdy/control when steering/operating at full speed
-Fuel efficiency
-VesselView - Really awesome feature

Cons
-Sensitive fuel system
--- you could put fire wood in the old 2 stroke and it would run.
-Significantly larger than the original 75hp 2 stroke
--- The proportions look slightly off... looks over sized for the boat.
--- When the engine is trimmed up, the motor takes up a lot of space at the stern
--- When the motor is trimmed up in shallow water, turning the wheel is difficult
-Faster top end (43 mph) but defiantly not the same torque
--- The old 2 stroke got up on plane much faster
--- I often wonder if i put the yamaha 70 on the back would i be happier with the reduction in top speed for a reduced plane speed...
-Heavy motor
--- I feel this contributes to a faster plane speed need.
--- Stern sits slightly lower in the water. when large wakes/waves come at the stern they sometimes crest over the stern plate. The old set up would float right over those wakes/waves

If i think of any more i will post.

Thanks for the feedback.