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8d CCA Ratings and new batteries

  • Thread starter Thread starter JLR
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I just went through a very similar issue. So, before you go too deep in the pocket, try this.
Start at the starters and clean every electrical connection all the way back to the batteries. Then check every thing in the junction box.
I run 6 Optimas (3 per side) to replace two 8Ds. Recently was unable to start the engine. It turned over very slowly. I found that the battery terminal connections were not tight. I cleaned and tightened them. Now they turn over faster and no more starting issues.
 
I just heard back from my Detroit guru. He said he pulled an old Detroit TSB that claims that the 40 MT starter on these engines requires 1900 CCA at 32 degrees. Is that possible and if so, who the heck has an 8D battery with 1900 CCA at 32 degrees. The Detroit book I have says 1400 CCA at 96 degrees.
 
JLR- If you use the paralleling solenoid you should be getting more than enough amps. If connections are good ,cables are good, and the batteries are new and it won't crank properly with the paralleling solenoid on ,perhaps the starter(s) are weak. Did anyone check the voltage and amperage while cranking?....................................Pat
 
Pat - not yet. All I know is there is not enough oomph to spin the engines properly and both are pretty much the same.
 
2 Group 27 AGM Optima Starting Batteries in parallel. 1100 CCA each (CCA ratings are at 0F, not 32F, so you have even MORE margin!)

Wire one set of these to BOTH starting terminals. The other 8D can be a deep-cycle and run house loads. Use a combiner between the two to echo-charge both from the other's charging sources.

That's how I'd do it - otherwise you NEED to use the parallel switch.

BTW my shop manual says 1800 amps required on a 12V system for a 6V92 or 8V92, so that's about right. My 45C had two 8Ds in parallel and even THAT was marginal in cold weather without block heaters.
 
Thanks Karl.
 
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