We have a Yanmar 4JH-2E that has been well used during the last 22-years. We purchased the boat
new in February 1995. The motor
has 2,900 hours on it and the boat
has spent four years in the very hot Sea of Cortez
I recently took all the plugs apart to look for corrosion
or loose connections.
Every connector was tight and clean. Every pin/socket was spotlessly clean with not a sign of corrosion. They looked like new.
That was the FIRST time in 22-years the plugs have been opened.
I also removed the Type B instrument panel and checked all the connections there. They were also perfect.
The only corrosion I've found in electrical
connections associated with the Yanmar is on the starter/solenoid. Our anti-siphon valve as installed at the factory was cheap
and leaky. It was positioned directly above the starter and dripped saltwater on it. I replaced that valve after the first year but the corrosion effects continued.
Eventually I replaced the starter and solenoid and now, after two more years, they look like new.