Quick Diesel engine question

[Secondshift]

Ours was plumbed around .
A coverplate would be an awesome alternative to the sad reminder I get everytime i check the oil.

Thanks.
Best Regards

[Secondshift]

I mentioned aftermarket components earlier but having heard that runaway scenario I think I'd prefer mine to in a little Yanmar box. Even at twice the price.

Regards

[waterman46]

Always should install an adjustable pressure switch in line with the electrical pump if you use an automotive/truck electrical fuel pump, and you can adjust the pressure to a minimum needed to pump fuel to the engine.

The electrical fuel pump is usually only needed for bleeding, if your engine is close to same height as fuel tank (true with most small boats). The electrical fuel pump should be installed so that it has a bypass with valve. Shut the bypass valve only when needing to use the electrical pump for bleeding. After bleeding, shut off the electrical pump and open the bypass.

[a64pilot]

Originally Posted by waterman46

Always should install an adjustable pressure switch in line with the electrical pump if you use an automotive/truck electrical fuel pump, and you can adjust the pressure to a minimum needed to pump fuel to the engine.

The electrical fuel pump is usually only needed for bleeding, if your engine is close to same height as fuel tank (true with most small boats). The electrical fuel pump should be installed so that it has a bypass with valve. Shut the bypass valve only when needing to use the electrical pump for bleeding. After bleeding, shut off the electrical pump and open the bypass.

You really don’t need to do any of that. Just buy a low pressure pump, there are many, most meant to feed carburetors, as if there is much fuel pressure it will overwhelm the needle / float and flood the carb. The high pressure pump doesn’t care if it gets 2 or 20 PSI of fuel, so long as there is pressure. There has to be of course an upper limit, I don’t know what it is, but I bet it’s pretty high.
It’s true a Diesel will pull fuel and run without a boost pump, but you want or need a boost pump for the exact same reason you need one on your watermaker, that is that if the HP pump is forced to pull the liquid it could cavitate, and cavitation will damage most if not all HP pumps.
So we need a boost pump, an electric will work just as good as a manual, and every electric fuel pump that I have experience with, fuel will flow thorough even if the pump fails or is off.
For that matter, the same for a manual pump as I have yet to see a gerotor factory fuel pump.

[Secondshift]

None of the info I gathered when researching an additional pump suggested a pressure regulator or release set up.
Low pressure pump within engine spec. and
similar application were recommended .
The PO stated the ones we have were for a small diesel tractor.

Best Regards

[MicHughV]

yes, my Yanmar also has the two pumps...mechanical on engine....electric in-line....factory install...was told it is for bleeding purposes....told they can operate independently of each other...
modern day diesel engines, like the Yanmar, have a "self-bleeding" system, and I believe that is the purpose of the electric pump...you can bleed the fuel lines without cracking open any bleed points, injectors, etc.....or pumping the little hand lever on the mechanical one...

[skenn_ie]

If the electric one is a pressure pump, as in it slows considerably if you block the outlet, it will likely severely restrict flow if it isn't spinning. A certrifugal one, installed immediately below the fuel tank, should do what you want. You may need a bleed valve though, in case it gets airlocked. The other alternative is to install a bypass valve beside the pressure one, but make sure the pressure/suction to open the valve is quite low. Personally, I prefer a mechanical lift-pump that has a primer lever or button. I don't like vital systems to be dependent on electrickery.

[Ox76]

I know if the electric pump is a diaphragm type pulse pump it will draw through. This is from personal experience.

[ejjawhite]

I have a Yanmar 3 HM35F and there is no electric fuel pump.

[guitarrich]

Some electric pumps incorporate a filter. I hadn’t realised this, and badly missed my generator for the last week of a transat. It would start, run for a short while then stop. Eventually it wouldn’t run at all.
I’d serviced that engine during 3 years of faultless behaviour, but never knew the electric lift pump contained a filter that was slowly clogging up.
Back in home waters I dutifully noted down the serial numbers and bought a new pump from a Kubota dealer near Falmouth. After fitting it, I was more relaxed about pulling the old pump apart. What a wazzock! I gazed in wonder upon the filthy filter that came out of the end housing with mixed emotions, but mainly regret for all the additional engine hours I’d added to preserve the contents of the freezer etc etc. (I did have an engineer on board - and he didn’t spot this. Another wazzock!)

[Icarus]

Originally Posted by ahun

Yanmar 3HM35F engine. It has two fuel pumps, one on the engine and an electric one in line.

If the electric one fails during normal engine operation, should the engine side fuel lift pump be able to pull the fuel through the failed pump? If it doesn't, does it mean it's faulty too? Or could there be any other reason why it doesn't?

Thank you.

If the fuel tank is mounted low and the fuel level falls the mechanical pump can have problems sucking up the fuel because the head increases.
We have a tank in the keel and found when the tank empties to about halve level the mechanical pump is not strong enough to supply fuel to the injection pump.
Mounting an electric fuel pump solved this problem.
So I say yes there is a reason why it's there.

[ahun]

Thanks everyone for your input, lot of useful information came together.

During the week the two fuel pumps arrived, so this morning was fitting time.

First came the 'blow test'. The electric fuel pump indeed let's through the fuel when it's not operational with practically no resistance. It's a generic, low pressure fuel pump $16 from eBay, consumable.

I fitted both fuel pumps, bled the system, then went for a test drive. I turned the electric fuel pump off (I put a switch on its wiring) and the engine kept going. Meaning, the fuel lift pump provides enough fuel as normal.

Not for long, in about twenty minutes the fuel starvation started, then the engine stopped. I had to bleed the system again, then I kept the electric fuel pump on, and never had a problem again for the rest of the two hours.

Yanmar 3hm35f engine, fuel tank under the floor, slightly lower then engine, electric pump was not factory fitted.

[skenn_ie]

Suspect the breather is blocked. Try the test with the filler cap loose. I had a car that did something very similar. It was fine up to maybe 40MPH. If I drove faster, it would cut out. After a few minutes, I could restart and drive ... up to 40 again. Eventually, I found a patch of paint from the inside of the tank had curled up and got sucked up the fuel pipe.

[Secondshift]

Not for long, in about twenty minutes the fuel starvation started, then the engine stopped. I had to bleed the system again, then I kept the electric fuel pump on, and never had a problem again for the rest of the two hours.

Yanmar 3hm35f engine, fuel tank under the floor, slightly lower then engine, electric pump was not factory fitted.[/QUOTE]

Plus side. You have your back back!

A lot of questions could come from your test report.

Was anything specifically changed between running fine and fuel starvation

(IE rpm, sea state, in gear, out of gear)?

Did air visibly evacuate during the bleed ?

If so how much and where ?

Did you check the entire fuel line system starting at the tank as many suggested?


If there is a restriction somewhere or if a fitting isn't right it can cause air to be pulled into the line at a connection. The electric pump may be keeping the positive pressure. A fitting can sometimes leak air but not fuel.

As previously mentioned the high pressure pump is lubricated by the fuel. I wouldn't want to continue having this failure.

Best Regards

[ahun]

Brand new fuel lines, breather line, tank, new filters etc. Actually, I didn't check for bubbles or anything after the engine stopped, had to keep going in light winds and close to shore, so just problem solved quickly. Maybe will try again.