LOW ENGINE RPMS ON YANMAR 75


Ben and Gayle Super Maramu #347
 

I bought my SM in Feb 2015  and there are still many systems I need to better understand.  Most perplexing is I have seen declining engine RPMs since original survey.  Originally boat produced about 3100 RPMs (Yanmar manual says 3600/3800 tops - but I do know Autoprop may limit that number)  but has since declined to 1800.  Not sure why as engine seems to run fine - easy start, no smoke, no roughness at any RPM.  Racor and engine filters are new.  Manual shut off valve in passageway  is wide open (it actually will not shut off motor... but that's another issue).   I do have an Autoprop which was serviced well over a year ago - but not sure - by previous owner. Only other engine oddity as it runs very cold - never over 130F.   Boat has been in the water now for a little over a year with not much motor use.  Any and all suggestions would be welcome. 


Ben Driver

SM #347

La Bella Vita


seafeverofcuan@...
 

Ben, everything you describe points to a dirty prop and hull. Heavy marine growth particularly on the prop can virtually stop engine. Does it rev freely when in neutral? 
The correct running temp. is 80C around 175 F easily checked with a laser temperature reader to confirm validity of your gauge.
Regards,
Trevor Seafever
SM 425 Redline
Mexico
FOR SALE
$295K






---In amelyachtowners@..., <joedoakes66@...> wrote :

I bought my SM in Feb 2015  and there are still many systems I need to better understand.  Most perplexing is I have seen declining engine RPMs since original survey.  Originally boat produced about 3100 RPMs (Yanmar manual says 3600/3800 tops - but I do know Autoprop may limit that number)  but has since declined to 1800.  Not sure why as engine seems to run fine - easy start, no smoke, no roughness at any RPM.  Racor and engine filters are new.  Manual shut off valve in passageway  is wide open (it actually will not shut off motor... but that's another issue).   I do have an Autoprop which was serviced well over a year ago - but not sure - by previous owner. Only other engine oddity as it runs very cold - never over 130F.   Boat has been in the water now for a little over a year with not much motor use.  Any and all suggestions would be welcome. 


Ben Driver

SM #347

La Bella Vita


jjjk12s@...
 

Ben,

 

For the RPM - something super simple to check first - have you disconnected the throttle cable and checked the revs by directly operating the lever on the fuel pump? Without any other symptoms maybe your throttle cable has gradually become badly adjusted.

The cold running might be due to someone having removed the thermostat or the thermostat not working,

 

John Maramu #91 Popeye (with a Yanmar 75)