2000 70hp Johnson RPM ?

[tracker14437]

I Have a 2000 70hp Johnson, dealer said this motor has to be run between 5000 and 6000 rpm's at wot and full trim. Any more or less will damage engine. With boat loaded best operating range is 5500 rpm's. I understand higher than 6000 will damage engine. Could someone tell me why lower rpm's (say running at 4500 rpm's) would damage the engine.

 

[snapperbait]

Re: 2000 70hp Johnson RPM ?

The dealer's full of "you-know-what" if he says less rpm will damage the engine... Your 4500 rpm (about 3/4 throttle) is just about the perfect cruze/economy speed for that engine and operated at that speed, the engine will last longer than if used at WOT all the time..<br /><br />However, I'm willing to bet that what the dealer meant was that the engine should be equiped with the correct Propeller as to allow the engine to operate at the suggested wide open throttle RPM, without going over or under the the suggested RPM point...<br /><br />So since you say your engine is turning 5500 Rpm with a full load at wide open throttle, you have the correct prop and all is well...<br />

 

[jegervais]

Re: 2000 70hp Johnson RPM ?

It's prefered to keep in the mid to upper end of the range - and you're there.<br /><br />If your WOT rpm were say 4500, that basically "lugs" or overloads the engine. It creates excessive heat and stress and the engine life is adversly affected.<br /><br />It's like hooking up a 20' boat/motor/trailer combo to a little Ford Escort or Chevy Chevette and always trying to start off in 2nd or 3rd gear...<br /><br />BTW, as long as you're propped to turn in that range, yes, you can cruise at lower rpm's - no problem there.<br /><br />Hope this helps,<br /><br />John

 

[Dhadley]

Re: 2000 70hp Johnson RPM ?

Turning it over 6000 will not damage it. It's a needle bearing, 2 stroke motor.<br /><br />Good luck!

 

[tracker14437]

Re: 2000 70hp Johnson RPM ?

Thanks for the help. I really appreciate it.<br />Best Boating sight on the web

 

[ob]

Re: 2000 70hp Johnson RPM ?

Tracker, I would prop it to turn nearer the 6000 mark.I don't know when John/Rude changed their wot range from 5500-6000 to 5000-6000 but on the 3 cylinder loopers I've run they like to rap out better than 5000 at WOT.Nearer 6000 will enable crisper throttle response and extend engine life due to reduced load.