Volvo Penta 5.0 GI RPM Very hi no Power of New Impeller change

Sounds like you cooked the prop-hub. Without starting the engine, put it in gear and see if you can turn the prop by hand. If you can turn it ... you need to replace the prop hub. You do have a spare prop right? If so, just change props and that should get you by until you can get the other prop fixed.

So what you are saying is that the boat runs, (moves through the water), but when you apply high or maximum throttle, the engine is revving high, but your speed is only moderate or slow?

If this is the case, then I suggest that there is one of two possibilities...

1. The propeller you replaced has the wrong pitch (i.e. too small pitch) and is designed for a higher revving moter such as an outboard. I assume a Volvo Penta marine engine would not be an extremely high revving unit. Solution - use prop with same pitch as the old one.

2. The propeller could have a hub fitted in the centre of the prop with some type of impact/vibration absorbing material inserted in between which connects hub to prop. The bonding material may have failed, allowing the prop to slip on the hub when full power is applied, hence the high revs, with no increased speed. Solution - Replace prop with identical unit or repair the hub to prop bonding.

Cheers

Tony

#2 ... the prop hub was cooked because it ran hot ... the hotter than normal exhaust goes through the prop and softens the prop hub ... so now it slips at full load.

Well, if you don't identify yourself by logging, you really don't deserve an answer, but if you read my second point, I have explained exactly what you said.

Mike,

You've got to keep the guys up to speed here.

If you've found that something suggested works/doesn't work, let us know.

Being a VP GI it's a small block GM V8, and as such probably (most likely) an S Type DP (Duo-Prop), and should max out at circa 4800rpm, light load.

That you get the boat speed, and the engine revs you've said, it would seem that the torsional damper drive hub has let go on only one of the props. That means only one of them is doing the driving.

You can test that by doing as previous post suggests. There should be NO movement available at the props, and I'm surmising that you are not built such you'd start the motor by swinging the prop. The reduction ratio is likely to be 1.68:1, in favour of the engine. OR, remove the prop/s and inspect the rubber bush/s. Damage is easy to spot.

Cheers,

Stu. (VP dealer-30 yrs)

Good point ... about swinging the prop. I probably should have said to disconnect the spark plug wires, if you are one of the 10 strongest guys in the world. :o)