Slave solenoids keep dying/frying - what causes this?

Last week (thanks to this forum), I found and replaced my slave solenoid on my 2003, 225HP EFI Mercruiser. I did this after working with the forum to troubleshoot and identified that my starting problem was solved when I jumpered the two leads on top of the solenoid (this being the solenoid on top of the block, not on the starter itself). I replaced that solenoid with a new one and voila, I'm back in business and the family is no longer worried about going out in dads boat and having to swim back to shore.

Got in this weekend feeling confident and started first time and from then on each time I needed to start it I had to short the solenoid again.

The only other thing that I can add to the story and I don't see any relationship is that the oil pressure and temp gauge don't register anything (but I don't recall if they did before either - new boat for me).

Any idea what would cause a slave solenoid to burn out like this? I can't find a wiring circuit that shows how these are wired to the rest of the boat, but sure could use one to help troubleshoot.

All help appreciated.

Thanks,
Jon

Re: Slave solenoids keep dying/frying - what causes this?

valid8r said:

Last week (thanks to this forum), I found and replaced my slave solenoid on my 2003, 225HP EFI Mercruiser. I did this after working with the forum to troubleshoot and identified that my starting problem was solved when I jumpered the two leads on top of the solenoid (this being the solenoid on top of the block, not on the starter itself). I replaced that solenoid with a new one and voila, I'm back in business and the family is no longer worried about going out in dads boat and having to swim back to shore.

Got in this weekend feeling confident and started first time and from then on each time I needed to start it I had to short the solenoid again.

The only other thing that I can add to the story and I don't see any relationship is that the oil pressure and temp gauge don't register anything (but I don't recall if they did before either - new boat for me).

Any idea what would cause a slave solenoid to burn out like this? I can't find a wiring circuit that shows how these are wired to the rest of the boat, but sure could use one to help troubleshoot.

All help appreciated.

Thanks,
Jon

Click to expand...

Are you getting 12 volts to the "slave"? If you are, is the ground side of the slave to a good ground? Connect your light / meter from the slave negetive terminal and a good battery ground point. Hit the key and if the meter / light register anything, the ground is bad. If nothing happens on the meter / light, connect them to the slave + terminal and do it again. If still nothing, check your feed from the ignition switch, then the neutral safety switch on the shifter.

Re: Slave solenoids keep dying/frying - what causes this?

Thanks for the help. I will check the first few today, but the last part about the feed from the ignition and neutral safety switch - how do I check these? I know the wiring must be ok since the engine will start with just the key 'sometimes' (usually in the morning)...

Also, one more addition to the story. I took out the two batteries supplied with the boat and replaced with a single, new marine battery. I don't know why I would need the second battery unless I tended to use electrical power when the engine was off - right?

Thanks,
Jon

Re: Slave solenoids keep dying/frying - what causes this?

04fxdwgi said:

is the ground side of the slave to a good ground?

Click to expand...

It is far more likely that the solenoid is failing to activate than it is "burnt out". Make sure it is getting 12V at the "small" terminal when you hit start and make sure that you have a good ground.

Re: Slave solenoids keep dying/frying - what causes this?

With the solenoid "working sometimes" is even more reason to be looking at the ignition and neutral safety switches and all thier connection to them. Dig around on this site and see if you can download a wiring diagram for your year / model Mercruiser. Wiring would be pretty close for all boats with that rig in them. Your best friend here is a good meter and a test light, and start following everything, checking voltages as you go.

1st rule....... Make sure all wire connections are clean and tight....... If there's corrosion, they gotta be cleaned. Corrosion / loose connection = resistance. Resistance = lower voltage to load (solenoid). (This happens inside a faulty switch, from time to time, making the switch useless)

Check from power source to ground, when you turn key to start, there should be 12 volts from the "B" teminal on ignition switch to a good ground (say the negetive side of the battery). If it's 12 VDC, then power feeding switch is good. If not, anything less than 12 VDC, then power feeding switch is NG and you need to start working back towards battery positive terminal from there. After you have 12 VDC at the "B" terminal on a start attempt, then move tester to the "S" terminal on switch and do it again, turning the ignition switch to start. If it's 12 VDC, then you are good to that point. If anything less than 12 VDC there, and it is 12 VDC at the "B" terminal, then switch or wire connection is kaput. If you have 12 VDC at the "S" terminal, then go to the neutral safety switch in the shifter (2 wires coming down from it). You get the idea... One step at a time. It's the only way to do it to eliminate any possible problem source. Time consuming, not so much, but tried and true method of troubleshooting.

On the battery thing, most boaters use 2 batteries and a switch so that you have an alternate source of starting power so you don't get stranded because of a dead battery. Like when you anchor for lunch, have the radio and what ever going, if you drain that battery, you can switch to other "fresh battery" and get her started. After she's started, switch to "both" and charge that one up off the alternator.

Re: Slave solenoids keep dying/frying - what causes this?

Did you use an OEM solenoid? I installed some sorry aftermarket solenoids before. But I learned.

Re: Slave solenoids keep dying/frying - what causes this?

get 2 jumpers long enough to reach the battery. next time it happens jumper + to the small yel/red terminal. click but dosent work: solenoid bad. dosent click, place neg jumper to the other small lug(the ground side) and try again. if it now works , the ground lead is bad/corroded.

Re: Slave solenoids keep dying/frying - what causes this?

Jon;

The first time I replaced one I used an OEM and it failed the second time I used the boat, so I bought from Merc, it lasted about a Month and then failed. I bought another Merc and put "Heat Grease" on it before the Mech installed it and it's been working since , over a year.

Tom B.

Re: Slave solenoids keep dying/frying - what causes this?

Bork said:

Jon;

The first time I replaced one I used an OEM and it failed the second time I used the boat, so I bought from Merc, it lasted about a Month and then failed. I bought another Merc and put "Heat Grease" on it before the Mech installed it and it's been working since , over a year.

Tom B.

Click to expand...

Tom - where would one put "Heat Grease" if one was to want to use it???

Thanks,
Jon

Re: Slave solenoids keep dying/frying - what causes this?

I put it on the body and the place were the screws went into the block, It wasn't well accepted by the Mech, all in good fun... He was getting tired of the problem too..

Tom B.

Re: Slave solenoids keep dying/frying - what causes this?

valid8r said:

Tom - where would one put "Heat Grease" if one was to want to use it???

Thanks,
Jon

Click to expand...

I think he's talking about Thermal Heat Sink Paste, the same kind of stuff put between a CPU and heat sink on a computer. No reason a "slave solenoid" should get that hot to need thermal heat sink paste, unless it is being used to crank an engine excessively, exceeding the duty cycle of the relay.

Never had to replace one, so I don't know.

Re: Slave solenoids keep dying/frying - what causes this?

Hi

Your right that's exactly what it is, again all I know is I haven't had to replace it again. the stuff is cheap enough, no harm no foul.

Tom B