Originally Posted by ozdownunder
I have a Sanya 2012 model with Onan 7.5 KVA.
I would like to know why they are not lasting 500 hrs like the book said?
My experience in delivery
trips of new boats fitted with the Cummins Onan MDKBJ 6/7.5 kVA genset is consistent with yours. First failure tends to happen before 50 hours and from then on I am told that they last a bit longer but not more than 100 hours.
I can explain the difference because the original impeller is very old by the time you use it the first time. I cannot explain the 100-hr approximate MTBF thereafter because these boats have an electric water lift
pump that keeps the thing well supplied with water
. I suspect the genset pump's design is bad or the rotor design or materials are bad.
A nice trivia finding is that if you have a setup like on these boats, with another pump before the built-in one,you can run forever with a broken impeller provided the pieces do not get stuck somewhere and restrict water flow. Fortunately in many cases all the pieces get together in a little space before the exchanger and they do
not block anything, hence the genset runs fine until you do schedule maintenance
and discover that the blades have disappeared.
Maybe we should do away with the impeller!