Manual vs electric fuel lifting pump

[Bowdrie]

Originally Posted by stormalong

Haven't had a mechanical pump failure yet.

I've worked on Nordic 44s, nice boats.
I know they have lots of wood for you to "knock on wood".

[stormalong]

Originally Posted by Bowdrie

I've worked on Nordic 44s, nice boats.
I know they have lots of wood for you to "knock on wood".

Thanks, owned 32 years. Second engine. I've done everything to it but paint and it needs paint.

[Jim Cate]

^^^^
Well, you may have been lucky, but mechanical pumps DO fail in the real world, and having a built in remedy that also aids in bleeding is a damn good idea IMO.

Jim

[pnw2022]

This thread got me to thinking.

I have a Yanmar 4JH4AE. A few years ago, the electric fuel pump died and the engine along with it. It was the original (~10 years old) pump at the time and I had always thought that maybe that this setup was just the way it is with that particular engine, etc.

I was able to troubleshoot enough on my own to isolate it to 95% being the electric pump but was near coastal (with lots of tides, rocks and no wind) and ended up calling in for a tow. This was around Cattle Pass south of Lopez and San Juan Islands up here in the Pacific Northwest on my way from Roche Harbor to Anacortes.

The silver lining was that I scored some difficult to find moorage in Friday Harbor for a week or so waiting on parts and the local diesel place was excellent to work with and replaced the pump and I put it on the list to pick up a spare along with the belts, impellers, and other 'consumables' that somebody should be able to easily self-replace in a pinch.

Anyway - I don't like the idea of the engine (once started) being dependent on electrical power if not absolutely necessary. I think, as somebody mentioned here or elsewhere, that taking some load off the manual lift pump is probably a good idea?

So my question is:
1. My fuel tank is about 1-3 feet below the lift pump depending on how full, although the external/racor filter is higher of course.
2. This particularl Yanmar (4JH4AE) did have an issue where they had some 'self bleeding' type situation for the lift pump and primary filter (same assembly?) which at one point, and I can not remember if it was before or after, I had updated to the 4JH5 replacement as the factory recommend workaround. Basically the 4JH4AE 'self bleeding' would itself wear out and cause 'hard to start' issues from air or something backing into the fuel line or pump.

Q1: Should the engine itself been able to pull fuel from 1-3 feet below the pump on it from the tank? Since it did not, possibly the way the Yanmar factory pump is built causes blockage or too much volume and if I had simply bypassed it with a bronze fitting I would have been fine?
Q2: If the above is true, probably the mechanical pump is worn out?

I guess I could test by installing a bypass around the electric pump and see what happens but thought I would ask first.

Thanks in advance. I have decent mechanical understanding but am certainly a diesel expert much less a Yanmar expert!

[Dalestr]

To answer Question 1: Most mechanical fuel lift pumps can handle at least 2' of continuous lift from the tank. The maker should have the actual specs. My 2GM mechanical Yanmar pump is rated 0.8m for dry lift. That said, I see some Kubota based engines by Beta Marine have a limited lifting ability and they sell a Facet cube style pump accessory. Not sure if that is for replacing or supplementing. Those cube pumps generally have very good dry lift capability, like 40" or more. Details are at Pegasus Racing.
I know of one boat that suffered an electric pump failure (Facet) after a good part of the season with a variable fuel blockage at the plumbing from the tank dip tube; particles almost totally blocked the fuel supply. Engine would slow down but not quit. With the high vacuum developed, air or gas 'boils' out of the diesel fuel and the electric pump works hard without much flow and probably in a gassy environment, reducing lubrication (the air or gas was then presumably diverted by the self-bleeding system). It remained functional until the pump died. The root cause was the blockage which was located after replacing pump. Fortunately, the distributor type injection pump suffered no apparent harm. It would have been easily diagnosed if a vacuum gauge was fitted. On this boat there was an indication; the priming pump button on top of the secondary filter would get pulled down.

On your Ques 2: It is interesting that the larger Yanmars are having issues with their self bleeding circuit as you describe. I was aware that the Euro-built version of the GM series engines, unlike the Japanese built versions, were fitted with odd self-bleeding where it appears to be a pressure bypass design to maintain sufficient fuel pressure (while many self-bleed systems have a simple open bypass with restriction). The bypass valving in this case can wear and cause hard starting problems. Toad Marine recommends reverting to a non self-bleeding system like the Japanese built version. Maybe they can't get replacement for that valve.
Mechanical pumps can eventually age and the diaphragm may crack and fuel leaks into the crankcase oil. This is another advantage for the electric pump as a replacement for a mechanical unit.

[bil56]

the problem of putting an electric pump AND the original mechanical feed pump online is the risk of a significant diesel leak in the engine oil pan, engine which risks self-supplying with oil diluted, which usually ends very badly ...

unfortunately Yanmar does not sell replacement pump membranes but only new pumps, so we installed an electric pump on a 1GM10, no operating problems, for the price (approximately €25) we bought 2 and we have the peace of mind for years
note: a metal plate with gasket has shut the location of the old pump

[capt jgw]

My two Perkins 6.354's have mechanical lift pumps that work well and a prior owner installed Walbro electric pumps. They have separate on off switches so were apparently installed to aid bleeding. And these engines are a pita to bleed, three bleed screws each and the lift and injection pumps are on opposite sides of the engine. Takes two people to do it using the mechanical pump. I only run the electrics when bleeding the system, they make it a lot easier.