Re: 1948 Super Eight Resurrection

Posted by HH56 On 2015/10/19 11:11:30

It is possible one of the cells sulfated but I'd do a couple of checks before condemning it. Other than the specific gravity there is no way to check each cell individually unless it is one of the batteries where the cells are connected with external jumpers. If the specific gravity is low on all then I would make sure the cells are filled and then do a good charge and check again. Sometimes the tenders just don't have enough current output to charge a battery properly. I think the tender juniors may be one that has issues with that large battery as it never seemed to turn off on mine. 6.25 sounds OK but it might just be a surface charge and any real current requirements will make the voltage go away.

If the cables and posts haven't been cleaned recently I would do that again as a first thing to rule out any oxidation that has built up between the two. There could be some resistance at the terminals. Then use a voltage meter across the two battery terminals and see how much drop at the battery when the headlights are turned on. If the voltage holds fairly close then do the same test with headlights off and when the starter is cranking.

I don't have the lights connected so can't do that one but on my 356 engine the battery reads 6.28v just sitting. When I crank the engine it drops and fluctuates at around 5v +/- 1/10v. If yours holds in that voltage range the battery is probably OK. If it drops much with the headlight test or any below 4.5v with the starter I would make sure battery is fully charged and then redo the test. If it still drops then the battery is suspect.

It is possible there is another connection that is causing problems. If the voltage at the coil drops much below 4.5v then the spark becomes marginal. Possibly a ground connection or one of the connections between the battery and coil is causing issues. The engine being hot usually places a strain on everything so the electrical needs to be in top notch condition on a 6v car.