Starting a dual engine setup with only one motor

[svonmiller]

Greetings,

I'm not sure if anyone can help without seeing schematics, but I'll try anyway.

My IMP has twin 1991 EFI 5.7 Mercruisers. The starboard engine is at the machine shop getting rebuilt. Turns out the block is cracked. So while it's there, I want to startup the port engine to see if that block is cracked.

With one engine out, and all of the wiring disconnected for the starboard engine, I'm wondering if it would do any harm to the port engine if I start it up (protecting all the loose wires and making sure nothing shorts of course).

I guess my concern is around some vague memory of disconnecting a battery from a running engine and it damaging the alternator, or some such thing. Anyway, I thought I'd ask if anyone knows if this might cause damage to the electrical system. It's not a complicated boat, just your typical 1991 power boat with 350 twins. The port engine is all wired, it's just the starboard side that has the harness disconnected.

Thanks in advance!
Stan

[4bus]

Tie all the ground wires together of the missing engine together, you will be good to go.

[1BIGJIM]

You don't need to start it to see if the block is cracked. Put water to the engine, if the oil goes up you have a cracked block. If the other cracked because it was not winterized properly, more than likely both blocks will be cracked.

[svonmiller]

Thanks for the advice! Yeah I'll make sure those grounds are all tied.

I want to start it for other reasons. It's been sitting for three years, and I want to make sure that the port motor is going to run before I put the starboard one back in. I need to know if I'm facing another big bill.

It cracked because the intake was off and the engine filled with rain water and then froze. It was half torn down and covered, but the cover was leaking. The $1200 machine shop bill is my penance for being a half-assed idiot during repairs. The port motor I think was drained, but it was three years ago and I don't remember if I drained it or not. I may not have. There were lots of distractions back then. I guess the upside is that I'm getting lots of practice pulling and installing motors.

[REDS32]

Expensive lesson

[Audiofn]

Do you have dual or single battery switch? If you have dual just put the switch for that motor on and try and start it up.

[Audiofn]

I would put a new water pump in there first.

[svonmiller]

Yes I do have a dual battery switch. I switch that over too.

Once I see that it runs, and everything is okay... then it gets a whole new raw water pump (impeller and housing), complete tuneup and oil change, and the stern drive gets new seals and bellows. What started this whole long string of events was that the impeller housing on the starboard motor cracked, shredding the impeller and sending all of the little bits of rubber into the oil cooler, causing the engine to overheat even after a new raw water pump.

Of course before all of that happens, I have to get all of the 3 year old gas out of the fuel tank. I've been mixing it with a full tank of super, 5 gallons at a time in my truck. Slow process.

[seafordguy]

Once I see that it runs, and everything is okay... then it gets a whole new raw water pump (impeller and housing), complete tuneup and oil change, and the stern drive gets new seals and bellows. What started this whole long string of events was that the impeller housing on the starboard motor cracked, shredding the impeller and sending all of the little bits of rubber into the oil cooler, causing the engine to overheat even after a new raw water pump.

AudioFn is trying to avoid this happening again by telling you to change the impellor first. It could shred instantly - even if it doesn't over heat things you don't want those chunks of crap throughout your coolers....

I'd take the "better safe than sorry" approach considering the price of impellers.

[svonmiller]

Good point, I wasn't thinking in those terms. I've already ordered the new pump and it'll be here on Tuesday, so I can definitely swap it out before a startup.