1GM10 running issue under load. Help please!

[Boater Sam]

The battery is usually hidden away, so hard to hear / see any issues. When I checked the voltage I did hear a slight hissing noise, I guess off gassing. I stop started the engine maybe 6 times during our trip yesterday and the battery voltage is down to around 13.3 (no alternator attached), which I guess is still a bit high? The can still hear off gassing once in a while, but not really now. I was going to just use the battery until it was below 13v and then add a solar panel to it - not sure if this is safe / sensible? I'm not sure what damage, if any, I have done to the battery - is there anyway to tell? Battery still seems to be functioning properly and starting the motor no problem, but honestly I dont know how long I have had this overcharging issue. The alternator was destroying cheap alternator belts a few months ago, so I imagine ive had the issue a while. I changed to a better belt and it stopped shredding.

The rapid wear of the belt was your first warning sign.
If your battery has 6 screw tops or a single removable cover that you can remove to check the electrolyte level it may be a good idea to do so.
If it has been gassing it will be short of water.
If you leave it short of water it will quickly fail, loosing capacity first.

 

[Porthandbuoy]

Congratulations on finally identifying the problem, and kudos for letting everyone know.

 

[DoubleEnder]

Excellent thread, hugely educational.

 

[oldbloke]

Hopefully you have found the fault and not just a fault. The alternator is a large part of the load on a 1gm10 under any circumstance so I am not surprised that removing it let the engine spin faster.

 

[bamboozle]

Hopefully you have found the fault and not just a fault. The alternator is a large part of the load on a 1gm10 under any circumstance so I am not surprised that removing it let the engine spin faster.

Yeh, this is what I am a bit worried about. Removing the alternator is making the engine run sweet, but does that mean there is still a problem elsewhere? I'll make a plan to fix the alternator and will report back if the issue persists.

 

[jamie N]

Reassemble the alternator assembly to how it normally is. Fit a switch onto the exciter line. Start the engine and run it as you did during the test to find the supposed alternator fault, then flick the switch to engage the exciter. This'll show whether the fault is isolated to the alternator for a cost of under a £1, and without complicating anything.