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BristolTucker 05-20-2015 09:15 AM

Fuel Pump Noise
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So I'm new to having a diesel and I wondered the other day why my fuel pump continues to "purr" along with the ignition on, but the engine not yet started. It's a 1987 Catalina 30 and everything is in good order. The valve on the fuel return to the tank is closed so I figured that the pump would pump until it came up to pressure and then stop - kind of like my old 1967 MG Midget where I would listen for the pump to purr and then stop before I started the engine.

So am I just needing to get used to the purr continuing or should it actually stop? I'm wondering if the pump is starting to reach its life's end.

Oh, one other thing. When I open the fuel return valve the pump speeds up so I know that the fuel is running back to the tank. The engine runs fine by the way. I've replace the fuel lines last fall and everything went fine. I was getting ready to replace the filters this spring when I noticed the continuing noise and I can't remember if it was always there.

Any ideas?



Capt Len 05-20-2015 09:36 AM

Re: Fuel Pump Noise
over to your spare pump and see if changes the situation. The pump may be fading and bleeding internally.

BristolTucker 05-20-2015 09:56 AM

Re: Fuel Pump Noise
I like how you're assuming that I have a spare pump. New to me boat and I'm still getting the spares sorted out. Must be time to order one.....

Stu Jackson 05-21-2015 12:11 AM

Re: Fuel Pump Noise
There's nothing wrong with your pump. In the electrical system, it is designed to run all the time. If you have an M25 engine, the knurled knob can be kept closed. The pump will still run.

Poke around here (and read about bleeding, too)

Engines 101 - The BIGGEST & BEST collection of M25 Series Universal Engine Information on the Internet, plus some M35, too :)

Diesel Engine - C34

Bleeding 101,6377.0.html

Minnewaska 05-21-2015 06:33 AM

Re: Fuel Pump Noise
Why would the fuel return valve ever be closed?

For a moment, when I read about a continuous purring noise, I thought you might have been hearing the engine room ventilation fan.

BristolTucker 05-21-2015 08:00 AM

Re: Fuel Pump Noise
Thanks for all the help!

It 'sounds' like it's normal then, but I've now got a simple spare for peace of mind. I guess that the only reason to keep the return valve open is to either bleed, which I've accomplished, or to polish the fuel. I wouldn't want to put any unnecessary wear on the pump if it's not needed though.

I've got a few hours of motoring this weekend to move the boat and I'll likely polish the fuel with the valve open before I change the Racor and main filters. After our long New England winter with the fuel topped off and Enzyme Treatment added it seems like a good idea.

JimsCAL 05-21-2015 08:24 AM

Re: Fuel Pump Noise
I think you are confused. The valve in the fuel return line should be left open. The supply pump is sized to deliver more fuel than the engine uses at full power and the "extra" goes back to the tank. Do not run with the return valve closed.

Minnewaska 05-21-2015 08:28 AM

Re: Fuel Pump Noise
I would think the motor would flood with fuel, if you left it closed.

Capt Len 05-21-2015 10:23 AM

Re: Fuel Pump Noise
Normal operation , the pump would soon build up max pressure and hold it,clicking once in a while as engine takes what's wanted or it's internal spring loaded release valve leaks back.If it clicks fast ,it's either moving fuel down the line or back-pedalling internally. When I use it for filling day tank(no line blockage) it whirred. When I ran it direct to carb of stove the occasional clicking told me rate of burn . Same applies as an engine app;ication. Think solenoid pushing a spring loaded piston with leaky valves.

BristolTucker 05-21-2015 11:42 AM

Re: Fuel Pump Noise
I'll do some debug this weekend. Basically it's either supposed to bleed back to the tank or not. At this point it's pretty unclear if it's normal. Len, I understand everything you've said and I do believe it's a leaky valve somewhere.

The bleed valve just before the injector pump should just be used for bleeding. I think I'm correct in that. If not somebody can explain why it should be open because unless you're polishing the fuel or bleeding there's no reason to leave it open. The pump should provide a set pressure and stop unless something is leaking back or there is a pump diaphragm or valve issue.

Just my thoughts.

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