Keep blowing solenoids in 1985 35hp Merc

I have recently acquired an 1985 35hp Mercury. When running, it purrs beautifully however I keep blowing solenoids. I've checked my grounds and tested with a voltmeter and everything appears to check out. Am I missing something obvious? Today I put in a new solenoid, started it up and went for a ride. Once I got back to the dock after a 20 minute ride I decided to try the ignition again but this time nothing happened not even a click. This is the third solenoid I've been through, each one has done something similar - works for one ride and then fails.
I would appreciate and help offered as I'm banging my head here.

Re: Keep blowing solenoids in 1985 35hp Merc

Kegraham said:

I have recently acquired an 1985 35hp Mercury. When running, it purrs beautifully however I keep blowing solenoids. I've checked my grounds and tested with a voltmeter and everything appears to check out. Am I missing something obvious? Today I put in a new solenoid, started it up and went for a ride. Once I got back to the dock after a 20 minute ride I decided to try the ignition again but this time nothing happened not even a click. This is the third solenoid I've been through, each one has done something similar - works for one ride and then fails.
I would appreciate and help offered as I'm banging my head here.

Click to expand...

Starter's bad. Drawing too much current.

Re: Keep blowing solenoids in 1985 35hp Merc

j_martin said:

Starter's bad. Drawing too much current.

Click to expand...

Thats an interesting diagnosis. Is there any indicators other than frying the solenoids that are obvious?

Re: Keep blowing solenoids in 1985 35hp Merc

Is it possible to test the starter without having to buy a new one? Is it as simple as just measuring the volts going from the solenoid to the starter to see if it is higher than what is coming from the battery?

Thanks for your help!

Re: Keep blowing solenoids in 1985 35hp Merc

They make a cheep amp meter that you just hold against the wire and get a good indication of the DC current going through it. Usually they have 2 grooves, or hooks. One for lighting circuits, and one for starting motor type currents.

You just hold it against the wire and crank it. Probably should be about 75 amps. (just a SWAG, Scientific Wild A***d Guess.) There might even be a spec for it in the maintenance manual.

In my experience, these vertically mounted end brush motors fill up with brush dust till they begin to short out. As long as the battery can supply the extra current, it won't be obvious till the brushes are completely gone. They will, however, draw excessive current.

You could theoretically measure the voltage drop across the supply wire, but there's too many variables to make it a reliable measurement, even with lab quality instrumentation.

hope it helps
John

Re: Keep blowing solenoids in 1985 35hp Merc

Well, it's taken me a while to get back to my engine....
I was able to get my hands on a new starter and install it into the engine. Unfortunately the same thing happened. I was able to get the engine to crank over on the first try and had a beautiful ride, however once I came back to the dock, I tried the engine again and it wouldn't start. The solenoid was blown again!

Re: Keep blowing solenoids in 1985 35hp Merc

How is your solenoid grounded, case grounded or does it have the two smaller terminals, maybe take some pictures of the solenoid before you start it?