Engine More Quite At Same RPMs?

[theway]

Just now my engine rpms suddenly dropped and now when I got back to where it was 2200rpms it sounds as if it's around 1200-1500rpms. Anyone know what's going on?

Thanks a lot.

[theway]

It's a 1997 Yanmar 3gm30

[shakey doug]

Has your vessels speed thru the water also reduced? If so tacho or circuitry u/s or drive train slippage.

[theway]

I couldn't tell if the speed reduced because the sails were up with a decent breeze. I plan to test my speed next time to make sure I'm still getting my 4.5 knots @ 2200rpms. The engine just seems smoother and not as loud now... which seems like a plus but trying to make sure it's not a wolf in sheep's clothing

Update:
Two hours later the engine stalled when slowly motoring to the anchorage. I was at about 2000rpms. It wouldn't crank back up immediately with the throttle in a low position, so I throttled it up and it cranked, spewing black smoke and gunk for a few moments and then back to "normal".

I had a similar stall a couple months ago so I'm wondering if it could be temporary clogs in the fuel system (primary or secondary filters) that cause it to give out and seemingly be fine after. And my guess is the momentary black smoke and gunk is the unburnt stuff as a result of the stall.

[Captsteve53]

1) Start with replacing ALL your fuel filters,
2) Check clean air filter-or try running with air cleaner removed
3) Remove and check /clean Exhaust Riser
4) Is temp reading normal?
5) Is Engine oil level normal?
6) Is Engine oil pressure normal
7) Is exhaust water coming out normal?

Cheers Steve

[theway]

Originally Posted by Captsteve53

1) Start with replacing ALL your fuel filters,

2) Check clean air filter-or try running with air cleaner removed

3) Remove and check /clean Exhaust Riser

4) Is temp reading normal?

5) Is Engine oil level normal?

6) Is Engine oil pressure normal

7) Is exhaust water coming out normal?



Cheers Steve

1-3: I'll look into tomorrow

4-6: Has been normal (180f and 40psi)
(Oil change 5 months ago, level is good, checked a few days ago)

7: There was some white smoke 3 days ago at the beginning of a 6 hour trip, which increased with the rpms, it lasted for about 45-60mins and then exhaust was pretty clean, maybe some faint white smoke sometimes. I tested the smell and taste with my hand... didn't smell of diesel, nor taste of coolant... Was just strong exhaust.

[DumnMad]

Check the gear-box oil as well.

[mtarcher]

Have you checked your exhaust mixing elbow this season?

[SteveSails]

The engine running quieter while you had the sails up in a decent breeze makes sense, you just took the load off the engine so it's not working as hard.

As for stalling and 'spewing black gunk' that's a problem. See above posts, all good places to start.

[theway]

Originally Posted by DumnMad

Check the gear-box oil as well.

I checked this a couple weeks ago and it was fine, but I'll have another look today, thanks.

[theway]

Originally Posted by mtarcher

Have you checked your exhaust mixing elbow this season?

I haven't checked it in many seasons! But I'm going to look into it today. I want to check everything else first and confirm the symptoms.

[theway]

A: The air filter was a mess. It was definitely restricted... Very dark with a black powder, but the foam was in pretty good shape. I gave it a decent scrub and rinse, should be good until I can get a replacement. (I usually try to get as much clean air flow to the engine room as possible, hatches and engine door open, sometimes the cockpit lockers. But the engine room is quite tight on the P323. But I should be replacing it more often regardless)

B: Secondary fuel filter (the one on the engine) is fairly clean and still quite colorful orange. It should be as I run two Racor primary filters. Both are pretty new (4-5 months) I have seen the debates about 2 vs 1 primary Racor filters since 2 is more of a burden on the fuel pump. I can bypass 1 of the Racors with valves and will try that to see if it helps. If not then possibly new filters, maybe they clogged fast.

C: Cleaned the raw water strainer, wasn't too bad. I always have a decent flow coming out the stern. I was going to do a test which suggests ~3 gallons per minute shout output at 1400rpms, but my tach was not working at the time, which happens infrequent (always something huh) So I'll do the test when it decides to work again. And if significantly less than 3gal I'll take the mixing elbow off next port.

D: I'm also thinking it could be bad fuel... How common is that these days in Tahiti and Fiji? The last I got was 10gals from the small marina at Musket Cove in Fiji...

[ontherocks83]

Originally Posted by theway

A: The air filter was a mess. It was definitely restricted... Very dark with a black powder, but the foam was in pretty good shape. I gave it a decent scrub and rinse, should be good until I can get a replacement. (I usually try to get as much clean air flow to the engine room as possible, hatches and engine door open, sometimes the cockpit lockers. But the engine room is quite tight on the P323. But I should be replacing it more often regardless)

B: Secondary fuel filter (the one on the engine) is fairly clean and still quite colorful orange. It should be as I run two Racor primary filters. Both are pretty new (4-5 months) I have seen the debates about 2 vs 1 primary Racor filters since 2 is more of a burden on the fuel pump. I can bypass 1 of the Racors with valves and will try that to see if it helps. If not then possibly new filters, maybe they clogged fast.

C: Cleaned the raw water strainer, wasn't too bad. I always have a decent flow coming out the stern. I was going to do a test which suggests ~3 gallons per minute shout output at 1400rpms, but my tach was not working at the time, which happens infrequent (always something huh) So I'll do the test when it decides to work again. And if significantly less than 3gal I'll take the mixing elbow off next port.

D: I'm also thinking it could be bad fuel... How common is that these days in Tahiti and Fiji? The last I got was 10gals from the small marina at Musket Cove in Fiji...

how did it run after you did all of the above? My first thought to Black smoke would be a rich condition i.e. restricted air flow (like you found above) or excessive load i.e. fouled prop.

[theway]

Originally Posted by ontherocks83

how did it run after you did all of the above? My first thought to Black smoke would be a rich condition i.e. restricted air flow (like you found above) or excessive load i.e. fouled prop.

It ran fine for the 30 Minutes while repositioning my anchor today. But it seemed to run fine after the stall too.

In general it runs fine 99% of the time. But lately it just seems like less rev/noise/power at 2200rpms than there usually is. The hour of white smoke a few days ago, then almost stalling and then fully stalling yesterday indicates something is happening.

As dirty/clogged as the air filter was, there's no way it wasn't having an impact.

(Still seems to move the boat through the water about the same, maybe a little slower... but bottom could be cleaner too)

[ontherocks83]

Originally Posted by theway

It ran fine for the 30 Minutes while repositioning my anchor today. But it seemed to run fine after the stall too.

In general it runs fine 99% of the time. But lately it just seems like less rev/noise/power at 2200rpms than there usually is. The hour of white smoke a few days ago, then almost stalling and then fully stalling yesterday indicates something is happening.

As dirty/clogged as the air filter was, there's no way it wasn't having an impact.

(Still seems to move the boat through the water about the same, maybe a little slower... but bottom could be cleaner too)

The exhaust mixing elbow could still be a problem too. A restricted exhaust can cause just as much power loss as restricted fuel. You're going to have to go through each item one by one until you get it resolved. Just make sure you are thorough and don't necessarily stop when you find one thing, Just because you find a dirty fuel filter doesn't mean there isn't something else also, multiple "neglected" things can stack up and cause all sorts of havoc.