Engine went up over 5500 RPM at WOT the other day

[ccave04]

Was out on the water the other day and was cruising along at about 3500 RPM because it was a bit choppy out and had the dog and girlfriend with me. At one point I figured I would open it up and when I put it wide open the engine ramped up over 5500 RPM almost to 6000 before I slammed it back down... I assume this is not normal and was wondering where troubleshooting would begin?

Boat and Engine: 2000 Marada 198 SKE 5.0L Merc V8 / Alpha1Gen2

Thanks for any suggestions... Chris

 

[Fishermark]

Re: Engine went up over 5500 RPM at WOT the other day

Not enough information. What is the normal WOT for your boat? (Don't mean to ask what the manual calls for - I mean what has been your experience with the boat and wide open throttle?)

 

[Failproof]

Re: Engine went up over 5500 RPM at WOT the other day

Could be as simple as prop hub slipping, cavitation, engine coupler slippage, wrong prop installed at service, was this the first time opening it up this trip out? Did it repeat?

 

[ccave04]

Re: Engine went up over 5500 RPM at WOT the other day

Typically the engine was right at about 4800-5000 WOT, this is the first time it happened. I did not open it all the way up again because I wasn't sure if that is bad for the engine. My RPM gauge only goes to 6000 and I could feel the engine being over revved. No changes as it has been in the slip, I haven't had it out again since this happened and I just pulled it out on the trailer to get cleaned up for a camping trip, so I was gonna tinker with it while I have it out. But I may have to play with it while on the camping trip I guess to get some more symptoms nailed down..

 

[Failproof]

Re: Engine went up over 5500 RPM at WOT the other day

Can be as simple as growth disrupting water flow and alowing cavitation. If the motor suddenly overrevs but it feels like you drop off slightly that is what i would suspect. If it gets worse suspect drive componets. If it happens more in chop than calm suspect cavitation.

 

[Fishermark]

Re: Engine went up over 5500 RPM at WOT the other day

Go back out in "normal" conditions and try it again. If it still overrevs then the chances are good you have a slipped prop hub or an engine coupler going bad.

 

[ccave04]

Re: Engine went up over 5500 RPM at WOT the other day

Sorry for the delay in response, was out camping for a week. But while I was camping I had the boat with me the whole week and it got alot of usage. WOT was hanging right at 4800 - 4900 RPM the whole week, except the final day when I took it for a final run it went up to 5600 and I let of a bit. Now, it was a little choppy but definelty not very much so I am not sure if that would have caused it?

I am just wondering why it is kind of "coming" and "going" as you would say and not a constant.

 

[Scott Danforth]

Re: Engine went up over 5500 RPM at WOT the other day

my vote is for cavitation, probably weeds in the prop

 

[dingdongs]

Re: Engine went up over 5500 RPM at WOT the other day

if the prop has a rubber hub mark it with quality white paint on rubber and steel.if it slips again stop when ever and view prop.can be done by raising drive all the way up and see if marks have moved.could try a higher pitched prop too.