4 Stroke Question

[Tyson Ross]

Is it okay to run my new 90 hp Mercury 4stroke close to 6000 rpms "all day long" like the young service rep and the boat dealer claims I can w/out reducing engine life?
He says "it is made to run at high rpms all day otherwise it loads up". Engine mounted to 21ft toon.

[HavasuDreamin']

Originally posted by Tyson Ross
He says "it is made to run at high rpms all day otherwise it loads up". Engine mounted to 21ft toon.
I would call 100% complete BS on that. I don't know the four cycle O/B's very well, but you should be able to run any stock motor (especially an O/B) at low or mid range RPM without any load up at all. If it loads up, it is not set up properly.
On the max RPM, read your owners manual, or contact Mercury Marine in Fondulac, WI and find out what the red line RPM is for your specific motor. Do not rev your motor past the red line RPM. I also would recommend against running your motor at red line for extended periods of time..........its life will be shorter for sure.
Good Luck

[Tyson Ross]

Thats what I am saying. The service rep looked like he was 20 years old. I questioned the pitch of the prop that was on it also as it will redline even w/ 8 people in the boat. I will probably run a higher pitched prop to bring rpm's down a bit so I am not cruising so near redline (6000).

[TCHB]

I always like to prop to max rpm set by Mercury with a medium load in the boat. Yes I agree that sometimes these so called boat experts were selling cars last week.

[PV]

Merc rates the WOT rpms for the 90 hp at 5000 to 6000 . I try to get as close to 6K as I can without overreving, 5800 to 6000 is just right!!!! This is after you've done break-in as prescrib'd by the book!! You wiil NOT hurt these engines if you run them all day long within the proper rpm range!!! (assuming you can live with the price of fuel !! )

[TCHB]

I do not like to keep any engine at WOT for any length of time. I raced motorcylces for many years and tried to keep the throttle open most of the time but rarely kept it wide open for more than 20 seconds. Even when the you are WOT on a bike you are shifting causing the RPMs to lower.