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

wmubronco

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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?

I have not, I know I am definitely due for a new bottom paint job at end of season. Would be a good time to have hull checked.
 

wmubronco

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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?

What size prop you run on there? 3 or 4 blade?
 

wmubronco

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Real head scratcher now. Went out yesterday, engine sounded great, right up on plane, cruised at about 25mph/3000rpms, temp needle barely moved. Wow.

Beached it at an island for several hours then when we loaded back up to head back to marina, temp did its climbing antics again. Was able to ride for a bit maybe at half the temp gauge, but the engine just seemed like it was struggling bit.

Not sure why the signs of heating up again, just doesn't make sense.
 

alldodge

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What size prop you run on there? 3 or 4 blade?

Missed this post, I'm running a 21P 3blade and have a 1:50 ratio drive

Real head scratcher now. Went out yesterday, engine sounded great, right up on plane, cruised at about 25mph/3000rpms, temp needle barely moved. Wow.

Beached it at an island for several hours then when we loaded back up to head back to marina, temp did its climbing antics again. Was able to ride for a bit maybe at half the temp gauge, but the engine just seemed like it was struggling bit.

Not sure why the signs of heating up again, just doesn't make sense.

Have to agree, real puzzler it doesn't make any since if it is over heating. If its just the gauge then more explainable, but with the motor struggling this doesn't seam to be the issue
 

alldodge

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Also we don't know what your fuel pressure is under load
 

wmubronco

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Also we don't know what your fuel pressure is under load

Switched over to high side port, here's what it read after starting (about 35psi);



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?
 

wmubronco

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Jun 18, 2019
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Quick update. Temp seems to be in check, creeps up to just under half way point on gauge if I run at about 3200rpms, roughly 25mph.

Still puzzled by lack of top speed. Guessing now a lot has to do with the hull and much needed repainting. Assume the hull is soaked.
 
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