Yanmar diesel low on thrust?

[Robin2]

My 1GM10 engines are not producing much thrust and the engines do not seem to be reaching full RPM. They are new engines and they used to work fine.

The propellor shafts turn easily by hand so friction in the bearings does not seem to be the cause.

Another possibility is heavily fouled propellors - which I will be investigating.

Does anyone know if the engine will run smoothly but at a lot less than full throttle if the fuel filters are clogged?

I suspect that clogged filters would result in rough running or hard starting - neither of which is a problem.

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[snowleopard]

seems very strange that two engines should develop the same problem at the same time. things like damaged injectors would affect them unequally. you need to look for something which would affect both; i take it the fuel feeds are separate. the prop fouling is the most likely cause, it's really amazing how much bad fouling affects drag, on hulls or props.

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[Birdseye]

am guessing that you are sailing a catamaran. are you sure that it is lack of thrust as opposed to fouling of the hulls? on my cat, bad fouling causes just the symptoms you describe plus an unwillingness to tack - and bad fouling is usually seen by end June. quick scrub, and it doesnt re-appear that season.

failing the above, it has to be some sort of fuel problem if the supply is common to both. partially blocked filters would cut down the max fuel flow and therefore the max power output. wouldnt necessarily affect starting at all.

would be interested to know what you find

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[duncan]

just to pick up on the fuel filter thing - I have a somewhat larger Yanmar but it started straight away and ran fine only missing a few beats once at any revs (sort of thought I might have picked up a line or something so lifted the drive but it cleared on restarting.
Then, out the blue, it died running back across Poole Bay.
BarryH and Forbsie being on board (never travel without spare forum mechanics!) we (ha) removed the seconday fuel filter and it was pretty solid gunge. Cleaned and having washed out the filter in petrol (spare what spare?) we got back fine and sorted out the primary later - also a hell of a mess!
Soltron seems to have sorted the tank contents and the boat carries a lot of filters now (horse/stable/.bolted) but a good starting, clean running engine is no measure of the state of the filters!

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[Robin2]

Thanks for all the replies.

The main problem was a (perhaps 2) fouled propellor(s). I scraped the worst one last night with a scraper on the end of a stick and things improved enough to get back to my regular berth - flat calm evening , low tide, mirror calm surface - beautiful.

I must buy some filters to have in stock !!!

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[duncan]

glad you are resolving your problem

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