Volvo penta 7.4gi loss of top speed perhaps tied to slight thermostat overheating?

[alldodge]

Neutral is fine to start, but need to know if pressure stays up in gear (on the water) as power increases

 

[wmubronco]

Neutral is fine to start, but need to know if pressure stays up in gear (on the water) as power increases

Sounds good, able to get out there first thing tomorrow morning. Would you know what the low pressure side psi should be at idle?

 

[alldodge]

Pressures

 

[wmubronco]

Pressures


Then went for under load from idle to WOT (right around 4200rpms) and the pressure went to past the 40psi mark and stayed there. Does this seem normal?

On the flip side the boat seemed to run like it did at the beginning of the season, hitting 25mph at 3000-3200rpm and 30-32mpg at 4000-4200rpms... which all seems a little less lower than where it should be.... maybe the propeller accounts for too much torque and not enough top end speed?

Also had the ramping up of temp again, sadly.


Hope I'm getting close.

 

[alldodge]

pressed the 20Amp circuit breaker next to low pressure pump and heard a click.

Since it tripped once it may do it again, but that said there should be only one breaker for both pumps

Your speed is back up, and is probably the prop

No findings of why temp is going up

 

[wmubronco]

Since it tripped once it may do it again, but that said there should be only one breaker for both pumps

Your speed is back up, and is probably the prop

No findings of why temp is going up

So my psi on both low and high sides seems within spec? Wondering if it worth to check out the anti siphon on the tank, or if it was just the breaker that was causing my issue with speed all along?

Haven't pinpointed temp rising just yet but would lean towards the exhaust being blocked or possible the water pump does not have any veins in it to fully push the water out of the engine.

Any thoughts?

 

[alldodge]

Motor won't run without the pump, so last time it wasn't doing right wasn't the pump
Do check antisiphon valve and fuel lines to insure they are not collapsing

Water pump doesn't have any vanes?

 

[wmubronco]

Motor won't run without the pump, so last time it wasn't doing right wasn't the pump
Do check antisiphon valve and fuel lines to insure they are not collapsing

Water pump doesn't have any vanes?

I'll check the anti siphon today probably just replace it since its an inexpensive part.

The water pump on engine. I had previously posted pictures but could not see inside it nor feel with a long screwdriver. I'll assume its working but maybe the restriction of water out is in my exhaust passages. Perhaps the flapper melted or fell off.

 

[wmubronco]

Got back out there. Replaced anti siphon fitting at the tank and fuel line that runs to the filter near low pressure pump. Did not notice any change in performance. Also pulled out the 90degree elbow at the tank hoping there was a screen/filter down there, but its just a pickup tube in the tank.

Replaced the June fuel filter with another new one as well. Dumped the old contents and did not notice anything but a few flakes and nothing else. No water fuel separation either.

Struggling to understand why I only top out at like 30-32mph at 4000-4200 rpms.....

 

[alldodge]

Post 10

I can get it up to 4000rpms today, but still only pushes just over 25mph, this was not the case earlier in the season. I don't know if I ever pushed it past 4200rpm last season.

Now

Struggling to understand why I only top out at like 30-32mph at 4000-4200 rpms.....

I would look at reducing prop pitch

 

[wmubronco]

Reducing pitch to 18 or 19? Or even 17?

Need to check exhaust for the heating up temp.

 

[alldodge]

Guess I missed you current prop pitch, but rule of thumb is reduce 200 rpm for each inch of pitch change

 

[wmubronco]

Guess I missed you current prop pitch, but rule of thumb is reduce 200 rpm for each inch of pitch change

Stainless 3 blade, 14 1/4 x 21.

I have an aluminum one I found that 14.5 x 19, that will not work correct?

 

[alldodge]

Yes the 19 will work and get the rpm up more

 

[wmubronco]

Yes the 19 will work and get the rpm up more

Even though its 14.5 and I currently have a 14 1/4 on there?

Do I need a new matching hub for the 14.5?

 

[alldodge]

The hubs should not be different if the prop is made for a Merc, VP, OMC

 

[wmubronco]

The hubs should not be different if the prop is made for a Merc, VP, OMC

Changed out the stainless to the 14.5 x 19. Improved a little on power and speed.

My heat still a concern and still need to check exhaust cavities.

Aside from that, shouldn't this 7.4 fly? I mean do I need a lesser pitch prop even? Wondering what top speed could be...

Injectors all dirty perhaps? Is it recommended to add anything to fuel in attempt to "clean" up system?

 

[alldodge]

Aside from that, shouldn't this 7.4 fly?

What boat?

 

[wmubronco]

Four winns 245 sundowner

 

[alldodge]

Have to agree, your 4600 lbs, my Rinker is 4200 lbs and I have a 300hp 7.4 carb, and I can do 60 mph. Yours should do at least 50 mph with 385hp

Have you tried weighting the hull to see if its water soaked?