Volvo Penta 3.0 GS Running at high RPMs

[ammosman]

Hi,
I recently bought a 1998 Four Winns Horizon QX with a 135HP Volvo Penta 3.0 GS. I've begun to notice that the engine seems to be running at high rpms. According to some specs I found online when running at around 3,000 RPM the boat should be going about 26mph. However, when I am around 3,000 RPM I am only going a little below 20mph. I am concerned that something may be wrong with the engine.... Or is it just because it is 12 years old I should expect this?

 

[bruceb58]

Re: Volvo Penta 3.0 GS Running at high RPMs

If the engine is running at 3000RPM then it doesn't matter what condition the engine is in. Its a direct relationship between engine RPM, gearing, prop and the hull weight length that determines your speed. An old engine or a brand new engine will go the same speed at 3000RPM if everything above is the same.

First thing i would do is make sure you are really going 3000RPM with a shop tach and use a GPS to determine your speed,

 

[ammosman]

Re: Volvo Penta 3.0 GS Running at high RPMs

Checked the speed with a gps yesterday and the speedometer is fairly accurate compared to what the gps is showing. Currently, the boat has a 14.25 x 21 prop and the guys at the boat store even thought this prop might be a little big for this engine. However, if I went down in prop size my rpms would continue to increase, correct? I am going to check the tach later this week. I know boats suck gas but I am thinking the tach is going to be accurate as well, as this boat is really sucking the gas. What I've read should last five is only lasting two hours.

 

[Don S]

Re: Volvo Penta 3.0 GS Running at high RPMs

Are you trimming it correctly?

 

[ammosman]

Re: Volvo Penta 3.0 GS Running at high RPMs

I believe so... I have tried keeping the rpms steady and trimming it differently without getting up to speeds it should be running at.

 

[bnicov]

Re: Volvo Penta 3.0 GS Running at high RPMs

It could also be a prop issue, either the pitch is on your prop is different from the prop on the test boat or your hub could be spinning. How about top speed?? Is it close to the test boat??

 

[45Auto]

Re: Volvo Penta 3.0 GS Running at high RPMs

Wide Open Throttle (WOT) speed and RPM is a much more useful data point than an arbitrary mid-range RPM. As others have said, we could probably could offer more useful advice with WOT data.

Your boat's performance should be similar to the Four Winns 3.0 below, it shows 22 MPH at 3000 RPM on a brand new boat. What kind of load did you have in your boat? 20 MPH on a 12 year old boat (prop not perfect, engine not quite tuned perfectly, etc) is probably about right.