Merc 140 Alpha One High RPM's at WOT

[Jsiples]

I have a Merc 140 inline 4. On specs it says at WOT I should be between 4200 and 4600 RPM's. I am right at 4600 and think it is possibly dangerous. I have checked the hub on prop and everything else in that area and see no issues. Any other suggestions?

 

[Wotknot]

Re: Merc 140 Alpha One High RPM's at WOT

You don't say what kind of boat you have or year model, but you should be ok. However if you're determined to get your rpm's down, you've got 2 choices. Either don't run WOT or go to a higher pitched prop. For example if you've got a 21p, go to a 23p. Higher the pitch is the lower the rpms.

 

[Trent]

Re: Merc 140 Alpha One High RPM's at WOT

Leave it be... You will be fine.

 

[tommays]

Re: Merc 140 Alpha One High RPM's at WOT

Your set up fine its not required to run at WOT only that you can reach it

If you lower it with a bigger PROP it will only make the motor work harder and the boat will also perform worse


Tommays

 

[Don S]

Re: Merc 140 Alpha One High RPM's at WOT

You are fine.
Getting the rpm below the 4200 range would be lugging the engine and decrease it's lifespan. Over 4600 means you would be loosing speed and effeciency.
At the upper part of the range (where you are now) gives you quicker planing as compared to 4200.

 

[Jsiples]

Re: Merc 140 Alpha One High RPM's at WOT

Thanks all, I figured it was alright just wanted to ask some experts. By the way its a Sylvan 18', 1984. 8)

 

[backacres]

Re: Merc 140 Alpha One High RPM's at WOT

I had similar concerns with my boat when I first took it out on the water (Four Winns 190 wMerc/ 30L.). The WOT was over 4600 so I backed off on it until I made sure everything was OK. I verified that I had the recommended prop and found that my boat tach was reading higher than my shop tach (I tested two different shop tachs' and found similar results). Bottom line is when I subtracted the difference between the two, it was within the specs.

Enjoy!!

Jeff