Volvo Penta 2001 'extra' solenoid

[stevie69p]

Hi folks,

picked up the spare engine that came out of my boat previously from the last owner... Just been having a quick look at it today, as was originally led to believe by the broker that it had been seized, but it's definitely not, so I'm going to have a bash at seeing if it can run... I've had it turning over on the bench using the starter motor via jump leads and a fly lead to terminal 50 to engage the starter solenoid. No fuel supply as yet as I am waiting on some banjo fittings...

Anyway... below the starter motor there is mounted another solenoid, which had me confused, but now I have thought more about it, I think it may be a solenoid to isolate the ground side of the engine. There is a copper bar tying one of the lugs to the engine block, and I'm assuming that the main battery ground cable would have been going to the other large lug....

Am I on the right track with this? I'm only used to working on car electrics up to this point...

 

[VicS]

Hi folks,

picked up the spare engine that came out of my boat previously from the last owner... Just been having a quick look at it today, as was originally led to believe by the broker that it had been seized, but it's definitely not, so I'm going to have a bash at seeing if it can run... I've had it turning over on the bench using the starter motor via jump leads and a fly lead to terminal 50 to engage the starter solenoid. No fuel supply as yet as I am waiting on some banjo fittings...

Anyway... below the starter motor there is mounted another solenoid, which had me confused, but now I have thought more about it, I think it may be a solenoid to isolate the ground side of the engine. There is a copper bar tying one of the lugs to the engine block, and I'm assuming that the main battery ground cable would have been going to the other large lug....

Am I on the right track with this? I'm only used to working on car electrics up to this point...

Yes
It is an earthing relay.

Its presence indicates that the engine block is not used as the negative connection. The various sensors are the two wire type and the alternator has a isolated negative connection.

However the starter motor is not an isolated type so during starting the block is earthed by the earthing relay

IIRC its not the same on all versions but it is shown on some of the wiring diagrams in the owners manuals

See http://www.volvopenta.com/volvopent...lication_search/Pages/publication_search.aspx to download a manualif you do not have one

 

[stevie69p]

Thanks Vic, that makes sense now. I did notice that the sensors were 2 wire and wondered why they were designed like that.
The starter motor solenoid also has an extra connection on the control side, although I was just grounding the block directly at the starter mounting flange....

What's the thinking behind isolating the engine block?

 

[VicS]

Thanks Vic, that makes sense now. I did notice that the sensors were 2 wire and wondered why they were designed like that.
The starter motor solenoid also has an extra connection on the control side, although I was just grounding the block directly at the starter mounting flange....

What's the thinking behind isolating the engine block?

It was done to help prevent galvanic corrosion damage to saildrives. Later engines ( from MD2010 series B IIRC) had the saildrive electrically isolated from the engine block achieving the same result by a different means.

There were some other variations on the theme as well .

Refer to the relevant wiring diagram if you actually put this engine into service.

 

[stevie69p]

Thanks again Vic. Every day's a school day on the PBO forum...
I have the manuals at home, and will have a look at the engine that's now fitted on the boat and see if it's the same set up. At this point, I just want to see if this engine will run. If not, it will make a good source of spare parts.