YSM 8 Weirdness

[cguthrie]

My engine is acting strange in a couple of ways.
The persistent issue is that after running for a couple of hours it suddenly loses power. The RPMs go down remarkably. All we have is a oil pressure indicator and that seems fine, as does the exhaust water. When we let it cool down and restart it, it seems better and runs as normal. Any thoughts?

Does anyone else's prop gain barnacles and other sea life? When the boat sits for a week it grows things, despite me having painted it. This also seems to affect the power a lot -- it will barely move at 2 knots under full. Luckily, I can send my wife under the water to scrape off the barnacles.

Even being clean, my YSM 8 moves my 27 at about 4 knots at best and less in waves and current. Is this about normal for this engine in this boat? I know the 27 is considered underpowered.

Sitting in Biddeford Pool on my 50th Birthday. Glad to be alive and board.

[tjr818]

Hi Cliff,
We own Sainte, a wonderful CD27 with the YSM8.
We sail on Alton lake on the Mississippi river. During the summer there is very little current. I have never seen the YSM8 push us at more than 5 knots. That with a clean prop.
Is your wife available for other diving work?
Best of luck,

[Sea Hunt Video]

Cliff:

I am not a diesel mechanic. Your symptoms sound like a fuel supply issue.

I would check the following:

1. Fuel filters. Make sure they are clean

2. Fuel supply lines. Consider bleeding the fuel delivery system to make sure there are no air bubbles in the fuel supply lines, etc.

3. Fuel pump and injector. Check for clogging, dirt in fuel pump, etc.

I am sure real diesel experts will shortly post with much better, more accurate and more detailed suggestions.

Happy Birthday

[Duncan]

...The persistent issue is that after running for a couple of hours it suddenly loses power. The RPMs go down remarkably. All we have is a oil pressure indicator and that seems fine, as does the exhaust water. When we let it cool down and restart it, it seems better and runs as normal. Any thoughts?

Just a guess, but it sounds like a temperature issue, so perhaps it's worth checking the thermostat and the impeller?

Even being clean, my YSM 8 moves my 27 at about 4 knots at best and less in waves and current. Is this about normal for this engine in this boat? I know the 27 is considered underpowered.

I have a rebuilt YSE8 with ~100 hours, and I get perhaps a half-knot more (4.5 knots in calm water). I've checked various "prop calculators" and they suggest that this is about all that can reasonably be expected from this 7 hp engine. I think that reducing the pitch of the prop may help it rev a bit higher, but the calculators I've tried suggest that we can't reach hull speed without doubling the power.

I think that reckoning is supported by Cape Dory's change to the 14 hp Westerbeke a few years after introducing the CD 27.

I do have a 3 blade 12 X 7 prop I have been thinking of trying, but I don't expect more than maybe a 0.5 knot improvement, if anything. This is very close to the Yanmar recommendation of a three blade 12 X 7.5 prop turning at 1639 rpm (i.e 3278 engine rpm @ 2:1 reduction).

[bobc]

This could be a fuel tank vent problem. Check to see if the vent line is plugged, or, next time you lose power, try opening the tank fill and see if there's a vacuum.

[marka]

given that the engine suddenly loses power i second the notion of a fuel system problem. i had the same problem, sudden loss of power under load (engine idled fine). i replaced the fuel filter cartridge and all was well.

[cguthrie]

Interestingly the engine has been doing great the last two weeks. I've been running it a lot as I make my way down the coast -- now in Duck Island Roads, CT. Seems to be true that the boat is happiest when it is being used well.