Yanmar loss of power , help needed!!

ST840

ST840

Well-Known Member
Joined
22 Jun 2014
Messages
1,166
Location
Southampton
Visit site
Hello

I have a yanmar 6LPA DTP that lost power all of a sudden. Revs dropped from 3200 down to 2500, then all revs failed to register on rev counter and top speed was down to 10 knots from 22!!

Oil pressure and engine temp were good, no unusual smoke showing !!

Please, any ideas gratefully received !!
 
Sounds like fuel starvation. Change fuel filters, and water separator filter and fuel lines should to be cleared. Happened to me a few years ago on port engine, she'd be fine on the plane for a 10 hour passage at 3000rpm (16kts), slow to displacement @ 1600 rpm near destination, but then try to get back to 3000rpm was a problem, she'd labour and not get above 2400 rpm. We've used a fuel additive since when filling up and the filters never blocked again. Full service once year means change of filters. The year in question we had a very rough passage so could have been crap kicked up from the fuel tank sump that blocked the new filters so quickly. We normally travel on full tanks in rough weather to avoid disturbing any silt in the base of fuel tanks.
 
Last edited:
NDB said:
Thanks for your reply, it was rather choppy out there today so a blockage of crap churned up makes sense!!
Click to expand...

But that wouldn’t affect the rev counter - maybe two separate issues?

Not sure about Yanmars but on Volvos the counter runs from the alternator. Had the reading completely drop off twice on separate boats - first time a leaking raw water filter fried the alternator and second time (last week) the alternator belt shredded itself. You would have noticed both of these though assuming you looked in the engine bay.
 
Last edited:
Is there some electonic limp mode? Loss of power and instrumentation combined ....

Is the waste gate electronic? Elec failure wipes out the RPM gauge and the same system deals with boost ( or some other engine limitation) ....

Given the RPM issue this would seem to have its root in electronics .
 
Neil your boat got a fright at being taken out. It doesn't like leaving the marina

vPEe6j9.jpg
 
On a more serious note did you not have an issue with a list causing water to pool around the fuel intake? My first course of action would be to check the primary filters for water and check for diesel bug. First symptom sounds like fuel starvation but as noted this would not explain the rev counter issue. But I'd check nonetheless.
 
Maybe I'm missing something but surely the rev counters are just reporting what the engine is doing!

If the engine revs drop due to a fuel issue or turbo issue then the rev counter is going to report that, why would there also be a rev counter issue?
 
Richard.C said:
Maybe I'm missing something but surely the rev counters are just reporting what the engine is doing!

If the engine revs drop due to a fuel issue or turbo issue then the rev counter is going to report that, why would there also be a rev counter issue?
Click to expand...

Op said then revs failed to register - so unless it stalled - which is not reported - then it would seem a fault the appeared within moments of the apparent loss of power. So unless you believe in coincidence (I tend not to !) they are most likely related.
 
jrudge said:
Op said then revs failed to register - so unless it stalled - which is not reported - then it would seem a fault the appeared within moments of the apparent loss of power. So unless you believe in coincidence (I tend not to !) they are most likely related.
Click to expand...

Hmmm, yes note to self always go back and re-read the very first post before commenting.

I agree coincidence is a stretch. Could there be a voltage drop issue?
 
jrudge said:
So unless you believe in coincidence (I tend not to !) they are most likely related.
Click to expand...

Tough call, when things go wrong they go wrong in a sustained and combined attack on all fronts. You get punch drunk and then add to the problems. I dont believe in coincidence but Murphy sure does.
 
Hi all,
Ok, so , turns out it was moisture in the diesel combined with rough conditions churning up sludge from the bottom of the tank. Fuel fillers blocked and caused the drop in power. Weirdly at the same time what revs I had didn’t register on the gauge because of a dirty connection that decided to show its face at the same time !!!
Possibly going to need the tanks cleaned and polished.
BruceK , yes I do have a problem with a slight list causing the water to pool in the side deck scupper area where the fuel fillers are located. Not counting this out as the problem but, before I bought the boat it was stood idle for probably 6 months with half full tanks!!
Just goes to show that a surveyor that was supposed to do a FULL mechanical, structural and electrical survey can’t be 100% trusted !!!
 
Glad its diagnosed Neil.

I suppose you can be grateful the police weren't waiting at the mooring for you. It must have been lonely out there :p
 
NDB said:
Hi all,
Ok, so , turns out it was moisture in the diesel combined with rough conditions churning up sludge from the bottom of the tank. Fuel fillers blocked and caused the drop in power. Weirdly at the same time what revs I had didn’t register on the gauge because of a dirty connection that decided to show its face at the same time !!!
Possibly going to need the tanks cleaned and polished.
BruceK , yes I do have a problem with a slight list causing the water to pool in the side deck scupper area where the fuel fillers are located. Not counting this out as the problem but, before I bought the boat it was stood idle for probably 6 months with half full tanks!!
Just goes to show that a surveyor that was supposed to do a FULL mechanical, structural and electrical survey can’t be 100% trusted !!!
Click to expand...

Glad you discovered the cause and the remedy.
 
NDB said:
Hi all,
Ok, so , turns out it was moisture in the diesel combined with rough conditions churning up sludge from the bottom of the tank. Fuel fillers blocked and caused the drop in power. Weirdly at the same time what revs I had didn’t register on the gauge because of a dirty connection that decided to show its face at the same time !!!
Possibly going to need the tanks cleaned and polished.
BruceK , yes I do have a problem with a slight list causing the water to pool in the side deck scupper area where the fuel fillers are located. Not counting this out as the problem but, before I bought the boat it was stood idle for probably 6 months with half full tanks!!
Just goes to show that a surveyor that was supposed to do a FULL mechanical, structural and electrical survey can’t be 100% trusted !!!
Click to expand...

Which part do you feel the surveyed failed to recognize?
 
You must log in or register to reply here.

Share this page

Top