Recently I started a thread about raw-water pumps
on the Yanmar 4JH engine.
Some of my contributions to that thread were based on false information given me by a pump supplier. Here is the result of further investigation.
I have been quoted prices for a Yanmar 4JH raw-water pump
ranging from $723 to $803.
I have the one I removed from my engine
I have also been quoted prices for a Yanmar 3JH raw-water pump
ranging from $195 to $268
. I bought one for $195.
Each of these pumps is on my bench right now. Despite what I was told by a dealer, these pumps are identical in the housing and in all internal parts
. On the manufacturer's parts
list, the numbers are identical without any reference to the engine. This is confirmed by my own observation and measurements of the pump components.
Every part is interchangeable
between these two pumps except two
: the discharge port hose coupling (straight vs 90 degree) and the external drive gear
These two parts can easily be moved from one pump to the other. If you do this you can reduce the cost of replacing the 4JH pump
from more than $700
to less than $300.
If you want an engine ready spare pump
, you can purchase
a 3JH pump for about $250, a straight hose coupling for about $17, and a 4JH pump gear
for about $132. Install these two parts on the 3JH pump, and you have a 4JH pump for approximately half the cost of a 4JH pump from a dealer.
The dealers tell me this price
disparity is dictated by Yanmar as each of the pumps is a proprietary version of a Johnson Pump. I have no information on that, but the fact that a Johnson pump dealer falsely told me there were internal differences in the two pumps gives cause for doubt.