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nk235 04-18-2009 02:30 PM

Yanmar starting question
I have a Yanmar 3GMD on my boat that was recently professionaly rebuilt and ran 100% perfectly all of last year and I used it a lot. This year it started right up for the first time and ran perfect. However since then I have changed the oil and the secondary fuel filter which is a Racor located in a cabinet under my sink. The engine fired back up fine.

However it seems that the past few times I go the boat the engine is having a lot of trouble starting. It turns over fine but it takes me a while to get it going - more than it ever has before. Today it took 3 attempts for about 5-7 seconds each before it finally went. Once it runs, it runs perfectly and if I shut it down and wait 10 mins or so it starts right back up but if I leave the boat and come back the next day I have the same trouble.

Does this sound like an air in the fuel lines sort of thing? The only thing I can think of was I did something or air got in somehow when I changed the Racor but then once I get it started why would the engine run fine?

Also the previous owner placed a pressure guage on one of the outlet sides of the Racor and I did notice it reads 0pressure. I tried loosenign the vent screw on the top of the racor and pumping the fuel prime switch on the engine but never saw any fuel or air bubble leave the vent screw ontop of the Racor. Is there another way to bleed the fuel filter?


celenoglu 04-18-2009 02:39 PM

It a good idea to bleed the whole system. If air is present some where it might be causing fuel feed problems to the pump while starting. That air might stay some where else and return back to original blocking point after the engine is stopped.

SJ34 04-18-2009 03:11 PM

Sounds like a fuel delivery problem or you have air in the line. If you vent the Racor (primary filter) then pump the lift pump, you are probably putting air into the system. The racor is under a slight vacuum so opening the lid hold down screw and pumping the lift pump can draw air into the system.

Open the vent on the secondary filter on the side of the engine (pressure side of the lift pump) and activate the lift pump to purge air. If air has gone past the secondary filter you will have to purge up to the high pressure pump and maybe even to the injectors. Consult your Yanmar manual for bleeding the HPOP and injector lines.

Your Racor should have 0 pressure (maybe even a slight negative pressure) as it is between the lift pump and the fuel tank, unless you have a boost pump (not common).

If you get little or no flow from the secondary filter while bleeding, your lift pump may need to be replaced. Your symptoms sound similar to mine when the diaghram in the lift pump went out.

bubb2 04-18-2009 03:42 PM

Bleed at the banjo bolt on top of the injector. Open the bolt a little and pump. If you see foam you have air. When you pump and see just fuel the air is gone. You can also bleed at the top of secondary filter. The little bolt right on top.

nk235 04-18-2009 04:30 PM

Thanks for the suggestions so far. I have already tried bleeding air at the fuel filter that is connected directly to the engine. I tend to think the problem is at the Racor fuel filter since that is the one I changed out and I can't figure out how to bleed it. Do all Racor's have their own litlte pump on them? I couldn't seem to find mine.

Secondly if the problem is back by the Racor, would bleeding the fuel filter on the engine eventually force the air out?

Gary M 04-18-2009 06:37 PM

Yes if you should be able to bleed the air out at the secondary filter however the Racor should have it's own vent. One tip I picked up here and put on last year was to install an outboard type priming bulb just where the line comes out of the tank.
Then to purge air all you do is go to the first filter and open the vent, pump the bulb till you see solid diesel come out. Go to the secondary filter and repeat. On my 2GM I have never had to bleed off at the injector.

If you engine starts and runs fine for say 15 minutes or so then I would think you do not have air in the lines.

Another thought you could have an air leak, check all you connections.


boatpoker 04-18-2009 07:06 PM

Always check the simple things first. Is your filter cartridge on tight and is the gasket seated properly ?

captbillc 04-18-2009 07:09 PM

on a racor filter without a priming pump on it , installing a ball valve on the inlet side of the racor makes bleeding the air easer. to change the filter element, close the valve, drain the racor, & change the filter. then fill the filter with fuel, open the valve & pump the engine pump to bleed the air out at the engine filter. i have a racor 500 . it does not have a priming pump on it. i have an electric pump between the tank & the racor which makes bleeding the system easy.

DrB 04-18-2009 07:43 PM

If the engine does start, but
not on the first 5 seconds, then it is not air, at least not likely, since the motor stays on once you get it going.

When diesels get below say 50 deg F and they don't have Glow Plugs, like a lot of Yanmars, they take a little longer to catch. You're located in LI area, it's April and still cool out, so that is more likely your issue and not air. Also supporting this theory is that once you get it hot, it starts right up, but you let it sit for a day, it is harder to start again. Once the outside and water temps go up little, I bet you motor fires right up.

Last year I fired my motor right up after a 5 month slumber on a the hard on a 75 deg day. 3 days later it was in the water (40 deg F) and the air was 41 and it took a few attempts to get her going.


SteveInMD 04-18-2009 09:19 PM

It sounds like you do have an air leak. First you need to start at the tank and check every connection. Make sure every clamp is snug and the filter is properly put together. Next, you need to properly bleed the entire fuel system. I mean no offense to anyone, but none of the posts above tell you how to do it right. I'm going to look for an old thread that provides the right procedure, and post it here in a few hours.

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