9 blade impeller versus 12 blade impeller

[Scubaseas]

Originally Posted by skipperpete

Stick with the Yanmar impeller but only if it has the thread into the bronze spline to accommodate the Yanmar impeller removal tool. It’s a bugger of a job when the impeller gets stuck and you have to remove the pump to use the conventional jabsco impeller puller……. Unless you happen to be lucky enough to have the forward facing pump.

This. Exactly.

[lestersails]

Originally Posted by NBs

As far as I remember, in my northen light generator, the original impellee had abundant wings and it often broke down...

If the impeller is the plastic part that pushes the raw water through the pump, isn't the impellee the raw water?

Sorry, couldn't resist...

[Jon Hacking]

We find that the Yanmar impellers last almost 1,000 hours in our 4JH2E Yanmars, but the 12-bladed imposters last about 200 hours. I guess you get what you pay for...

[Boatwright]

FYI: The old "Waste your Money" (West) Marine, no longer available, printed catalog has a very handy page for impeller identification, with part numbers.

We keep a copy around. They happen to stock the unusual shaft diameter needed for our old Volvo MD-11, also miraculously at a decent price. It's one of the few things I buy from them these days after becoming very tired of paying $10 for three electrical terminals, or $25 for a Chinese mooring chain shackle.

[bclaude]

I don't know the specifics of your engine but whenever possible I install a strainer on the raw water hose between the water pump">RAW water pump and either the heat exchanger or the bock if the engine is raw water cooled. In choosing the strainer I prefer those with a glass bowl so that I can easily check what has been caught by the strainer. Changing an impeller is an easy job but if the impeller fails then you have a real job on your hands finding all the loose bits in the heat exchanger of flushing the block until you can put the puzzle back together and verify you have found all the bits.

With a strainer in place you can easily check if your impeller is starting to shed pieces meaning it is about to fail in major way. If it does fail then all you have to do is clean the strainer and install a new impeller. In all impeller failures I have seen, small bits or an entire blade gets shed well before a catastrophic failure takes place and with a strainer in place, you will know it is time to act before its too late.

A heads up about the danger of failing impellers: When the RAW water cooling pump works as intended, RAW water gets mixed with hot exhaust gasses before it flows into the exhaust system which is made of plastic and rubber hoses and parts. If the flow of RAW water is severely reduced or stops altogether then the exhaust gasses are no longer mixed with water and will meet with the same plastic and rubber parts at a temperatures of 500–700°C (932–1293°F). The temperature inside the engine block will rise but not instantly because of the mass of the engine block and particularly so if you have a heat exchanger. This means that you have minutes during which your exhaust system is subject to very high temperatures it is not designed to cope with and your engine temperature alarm finally goes off informing you of an issue. At those sorts of temperatures, it does not take long to cause irreversible damage to critical exhaust parts especially on boats that are equipped with a dry exhaust (water separator in the exhaust system). For this reason I have installed an exhaust temperature alarm right after the mixing elbow. If the impeller fails (which happened to me once) then I can react immediately and avoid those critical minutes when damage occurs to the exhaust system.

All this to say that the impeller on a boat which usually last a full season and still looks pristine is IMHO the last piece of kit I would try to save money on.

[RaymondR]

Originally Posted by Jon Hacking

We find that the Yanmar impellers last almost 1,000 hours in our 4JH2E Yanmars, but the 12-bladed imposters last about 200 hours. I guess you get what you pay for...

I doubt that Yanmar actually manufactures the impellers, on the two yanmar engines I have owned the pumps were manufactured by Johnston and big savings could be realized by buying from Johnston stockists rather than as Yanmar spares.

[Rotten Ricky]

" I install a strainer on the raw water hose between the RAW water pump and either the heat exchanger or the bock if the engine is raw water cooled. In choosing the strainer I prefer those with a glass bowl so that I can easily check what has been caught by the strainer".

I like your thinking of a back up strainer and I will try to do the same, as I try to do with everything on my boat. I always carry a spare impeller. I have added small and inexpensive indicator lights to many of the electrical circuits (e.g. preheat) which prove at a glance if a device is actually getting power.

Also, I believe that some impellers are made of rubber whereas the better ones are made of the higher-quality neoprene and that could make a big difference. However I am happy if someone more knowledgeable will advise differently.

Cheers, RR.

[skipperpete]

Originally Posted by David Mathis

As to capacity, is 9/9 more than 12/12? I've used the cheaper aftermarket impellers on my Yanmar generator for many years without issue. The impeller gets changed about every 4-5 years with no failures or heating issues. The generator runs a lot since we have 120V refrigerator, freezer, ice maker, dual air conditioners, etc. We live on the boat much of the summer and anchor often. As to difficulty in removing the impeller, the first time changing was challenging until a sharp chisel was used to remove the vanes then it came off without difficulty. Now, Neverseize (an incredibly messy graphite/grease product) is applied to the shaft before installing the new one which greatly eases the removal.

All good advice for your generator David Mathis you obviously know your genset very well……but often generators are the worst for eating impellers, especially if the genset is mounted higher above the waterline or is a 2 pole alternator, having an empty suction line to the raw water pump is bad for impellers and when you have an engine that starts and runs instantly to over 3,000 rpm, it can be a very short life for an impeller. Adding to this, a lot of installations use exhaust splitters that drop the raw water flow from the exhaust back into the sea below the waterline so the opportunity to do the traditional “visual” of the exhaust is lost, the exhaust outlet is always dry.

[s/v Jedi]

The key to impeller life: the hose coming from the sea strainer must arrive at the pump from a point higher than the pump. This ensures that after engine shutdown, a column of raw water is standing in this hose, flooding the pump and impeller for lubrication next start.

I like to see the hose between seacock and strainer run vertical with the sea strainer top just above the waterline and the output fitting higher than the engine mounted raw water pump.

[svmatilda]

I too have a Yanmar 4JH2-HTE and have used the 12 blade with no noticable difference in operation.
If my memory serves me correctly the 12 blade is the one that will turn up using the part number from the genuine parts catalogue

[Mickeyrouse]

Originally Posted by RaymondR

I've had two Yanmars in my life and whilst they are great motors Yanmars parts pricing policies are a national scandal.

Years ago I had a 3GM30 which needed a replacement raw water pump. I was quoted $850 for the Yanmar pump which was basically a Johnston pump with a flange mounting onto a steel bracket. The same Johnston pump with a pedestal mount was $300. I purchased the pedestal pump and fabricated a bracket from a small piece of aluminium angle iron. It's about fifteen years later now and I still feel good about the $500 saving every time I remember the incident.

Not only that, but Johnston parts are widely available and much cheaper. Complete rebuild kits are available for Johnstone pumps, include shaft, seals, bearings, gaskets, plate, screws- everything except the body if need be. Most likely Yanmar uses an un-marked Johnston anyway.

As far as impeller service time, in 35 years with inboards, I’ve only had an impeller fail one time that wasn’t user (me) assisted by an un-opened seacoock after hauling or other service.

[s/v Jedi]

I have a Yanmar 4LH-HTE so older I guess but parts can be compatible for other models, just cross reference.

Here is some data I keep:

impeller 127610-42200 discontinued, now 127610-42270
= Johnson 1028
= Jabsco 17937-0001-P

Oil filter WIX 51344

[Disailor]

Also have a small clear bowl strainer on my 3ym30 immediately after the rawwater pump (RWP).
When my RWP developed a serious leak couple days before guests were to arrive I took the bearings n seal to a NAPA auto dealer. Since there are only about three manufacturers of ball/roller bearings the auto store can measure the bearings & look them up in a book that has all the bearings listed by size. Turns out the smaller of the two is the same as a chevrolet transmission input shaft support bearing: $3.00.

[s/v Jedi]

Here’s what I do with my genset: a small plastic Groco strainer with a custom diy insert made from thin wall pvc pipe. The holes are all smaller than the channels through the heat exchanger.

Also a tip: measure the channels in your heat exchanger and find a matching caliber ammunition… now buy a cleaning kit for that ammunition that had the pump stock as well as a copper brush. Now you have the perfect maintenance tool for your heat exchanger

[bbalan]

PJCruising,
Do NOT buy at 12 blade. I'll repeat that. Do NOT buy a 12 blade.
I posted about this here.


I have a 4JH2-TE and putting a 12-blade in created a difficult to diagnose, and very frustrating -- problem: no prime in certain conditions.



I can confirm that the problem has never recurred since we went back to a 9 blade.


All the sites that say the 12 is a direct replacement for the OEM 9 are just wrong.


Cheers,
Bruce