HELP! Replacing hoses on Yanmar 4JH2E with Kanzaki 4MA Transmission

dlochner · Mar 27, 2026

Search on line for a parts manual your engine. I found one for my 3JH2E, helpful even when not ordering parts. I've used Niemiec Marine (aka Diesel Parts Warehouse). They can look up the part number. Their service is great and prices are as good as anyone on the net. I don't price shop for Yanmar Parts anymore, lots of effort for very little, if any, reward.

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Ralph Johnstone · Mar 27, 2026

dlochner said:
Search on line for a parts manual your engine.

This is the only way to do it.

I replaced all my hoses at one time several years ago and several of them, on a 2GM20F, are custom bent and hold their shape.

It is not a difficult job (actually it's quite easy) if you replace the obvious shapes and diameters first.

dlochner · Mar 27, 2026

smokey73 said:
Thanks for the tip. I may be buying from them but the Yanmar's are shipped without the hoses and the installer puts them in so there is no part number or size listed on any websites. I'm still hoping someone here has replaced them and knows the size or can read a size on their existing hose.

Otherwise I'll have to remove the hose (probably by cutting it) and then see if I can match it. Marine Diesel Parts says it is just regular radiator hose but I'm hoping for something a little stouter since it will be in the raw water circuit. I guess reinforced radiator hose will work.

There are 2 different types of hoses, one type is is the preformed bent hoses which Yanmar supplies if original, they are painted gray. the other hoses are just marine grade reinforced exhaust/water hoses, there wouldn't be a part number for them.

Ralph Johnstone · Mar 27, 2026

dlochner said:
There are 2 different types of hoses, one type is is the preformed bent hoses which Yanmar supplies if original, they are painted gray.

Meh ............ maybe it's your English or maybe it's my comprehension but one of them is kaput.

The original hoses on the engine are covered with grey engine paint:

All replacent hoses are all bare black rubber.

dlochner said:
the other hoses are just marine grade reinforced exhaust/water hoses, there wouldn't be a part number for them.

Ahhhhhhh .... it's killing me to disagree with you but every scrap of rubber hose on a Yanmar engine has a part number and can be had from Yanmar at five times the cost compared to top of the line auto radiator hose sold by the foot.

Note that parts #2 and #5 are just straight auto rad hose, #2 is 1/2" ID and #5 I have no idea. Other hoses are custom Yanmar hoses. Everybody still has their own little part number and a price that will knock your socks off.

I don't know if this next idea is such a good one as the OP seems reluctant to order hose for his engine without a written list of hose sizes from someone else.

When I replaced mine, I looked at the hoses and saw that only about three or four hoses were custom made. I bought these from Yanmar otherwise it just wasn't going to work without collapsing the hose. Every thing else was bought by diameter and rough length (+ a few extra inches) as auto rad hoses. Part No. 6 was about $75.00 IIRC. I still can't get that number out of my mind for that short little piece of hose.

Why not order all of the custom hoses first from Yanmar first ? Then go after the straight pieces from your nearest auto parts supplier. If need be, label the straight pieces of hose and then pull them off the engine and go to the supplier and order the required material.

You're making a mountain out of a mole-hill on replacing these hoses. This was probably the easiest job I have ever done on the engine and you're going to feel the same way when finished. Slow and boring but definitely not hard.

dlochner · Mar 27, 2026

Ralph Johnstone said:
Meh ............ maybe it's your English or maybe it's my comprehension but one of them is kaput.

The original hoses on the engine are covered with grey engine paint:

If the custom preformed hoses are black, they have been replaced and are not original. If the custom preformed hoses are gray, they are original. Either way, the preformed hoses are only available from a Yanmar dealer.

As for the other hoses, wire reinforced radiator or Marine hoses would work.

Unless the Yanmar hoses are outrageously priced, I'd go with them. When the return line fuel hoses started to deteriorate and leak I opted for ¼" marine diesel hose instead of the Yanmar hoses. Turns out Yanmar return lines are 4mm and the spacing does not allow for a good hose clamp to seal the connection. They all leaked. I ended up buying Yanmar replacement hoses.

Ralph Johnstone · Mar 27, 2026

smokey73 said:
I guess the PO did not paint the hoses as they look like original hoses from 1994.

Now THAT is interesting. I just can't see how the engine arrived new without paint all over the original hoses.

smokey73 said:
I may be buying from them but the Yanmar's are shipped without the hoses and the installer puts them in so there is no part number or size listed on any websites.

And it's even more unusual that the engine arrived without hoses and the installer installed them at a later time. You'd think they would assemble the engine completely in the factory and be done with it. I can see all sorts of crawlers making a home inside the engine if it wasn't sealed up at the factory. But, I guess stranger things have happened.

I consider myself financially efficient (aka. cheap) and that's why I purchased all of the non-formed hose material from an auto parts supplier. I know the few formed hoses I did purchase from Yanmar were working their way up to $200.00 by the time I was finished. Just no getting around it in that case.

When I look at the cost of Yanmar oil filters at somewhere near $18.00 ea. today, I'm glad I purchase my oil filters by the case of 6 from Baldwin at $4.00 ea. The cost of Yanmar engine parts are terrifying and if I can buy the straight hose elsewhere, I will.

garymalmgren · Mar 28, 2026

I want to replace all the hoses on my 1994 Hunter 40.5 engine.

Why?

Davidasailor26 · Mar 28, 2026

dlochner said:
If the custom preformed hoses are black, they have been replaced and are not original. If the custom preformed hoses are gray, they are original.

Could be true for the JH series, but for future readers of the thread, it’s not true of all Yanmars. The YM series hoses are all black, even the preformed ones.

dlochner · Mar 28, 2026

Davidasailor26 said:
Could be true for the JH series, but for future readers of the thread, it’s not true of all Yanmars. The YM series hoses are all black, even the preformed ones.

By Gray, I mean the hose was painted gray, the hose itself is black. It may be the case that on other models or production runs Yanmar did not part the hoses.

Alan K · Mar 30, 2026

My experience with several vessels with Yanmar engines is that the engine and hoses (along with the hose clamps) are all painted gray at the factory. Replacement hoses from Yanmar are NOT painted. The only hoses that come painted on a Yanmar engine are the on-engine hoses. Hoses for raw water supply, fuel supply, fuel return, raw cooling water discharge and exhaust are supplied by the vessel manufacturer and are usually unpainted.

Davidasailor26 · Mar 30, 2026

For what it’s worth, this is how our 3YM30 came from the factory. All hoses, including the preformed ones, are just unpainted black rubber.

Ralph Johnstone · Mar 30, 2026

Davidasailor26 said:
All hoses, including the preformed ones, are just unpainted black rubber.

Seeing is believing.

Yanmar definitely had some reason for doing it like that. Aesthetics ? I've got to wonder if they employed someone who was very, very, very careful with a spray gun or they didn't install the hoses until after the block was painted and ignored the spray paint that got inside the hose connections.

One of the mysteries of the world

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