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Old 06-03-2015, 22:12   #1
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Join Date: Jun 2013
Location: Cairns
Boat: Southcoast 36
Posts: 97
Yanmar 3HM Fuel Feed Pump

Hi all,

Headed off on a sail yesterday and had a runaway engine when motorsailing. Engine gave a hiccup, a belch of smoke and away it went in extreme revs. Got it under control and it stopped after probably less than 30 seconds.

Engine restarted after a cool down and we limped back home safely by sail and using motor at barely an idle when needed in the harbour. No apparent damage, smoke or funny noises. It probably ran for 3/4 of an hour after the restart after the runaway.

Oil level has increased in sump and is less viscous. I noticed this when checking the oil before we set off. I had done a oil change a couple of months ago and thought i had maybe overfilled it. This is the first trip since the oil change. Have only done a couple 20 minute engine runs since the oil change just to keep it ticked over.

This morning, took off the crankcase breather and it is all clear.

Then took off the fuel feed pump. The diaphragm appears intact. However when i test it as per the manual by inserting a line from the inlet side into a jar of fuel and operating the lift lever, no fuel is lifted into the pump. When i put a finger over the inlet side and operate the lever i can only feel the barest bit of suction.

1) So, have i missed anything? Is the feed pump shot as I suspect and as a result, fuel has entered the oil sump leading to the runaway?

2) Will running the engine at idle with this fuel/oil mix as i did for 3/4 hr have done any damage? What should I check if any thing?

I have an electric pump upstream of the feed pump. The pump is an ECCO 1LM12 Diaphragm Pump which has a specified operating pressure of 2-3psi. The pump is wired on the ignition circuit with a separate switch so that it is normally off. I use it for bleeding only.

This electric pump is new. The last electric pump fitted by a PO had failed and i replaced. It was wired to the ignition but was on all the time when the ignition was on i.e. no switch.

According to the manual, the manual feed pump has an operating pressure of approx 1.4psi.

We sort of need to get to somewhere so am considering a workaround until i can get a new manual feed pump sourced and sent out.

3) Can i take the mechanical lift pump out of the picture and run using the electric only? Is the higher feed pressure of the electric pump going to cause a problem?

4) To do the workaround I would remove the manual pump altogether and temporarily blank off the opening on the crankcase. Is that the correct way to work around?

5) Will also do a complete oil change. Do i just do the change oil as per normal due to the diesel contamination? i.e. pump out the old oil, change the filter and refill with new oil.

6) Any one know of a good source of Yanmar parts for the 3HM in Australia, preferably Western Australia? Have not had a lot of success searching especially in finding an online parts ordering facility.

7) Is using the electric feed pump a viable permanent solution? Would probably carry a spare electric pump as a backup.

Thanks in advance

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Old 07-03-2015, 15:08   #2
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Location: Cairns
Boat: Southcoast 36
Posts: 97
Re: Yanmar 3HM Fuel Feed Pump

Bueller. Bueller. Bueller.
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Old 07-03-2015, 15:32   #3
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Re: Yanmar 3HM Fuel Feed Pump

Just bypass the mechanical fuel pump, change the oil and filter and you should be good. That is if the electrical fuel pump is 4 psi or less. You may be able to get a rebuild kit for your mechanical pump.
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fuel, yanmar

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