Systems+Engines

Dirty Ground

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Mark Karwowski of San Francisco, California, asks:

"Recently we had trouble starting the diesel engine aboard our Nordic 40. Although all the lights and other electrical equipment aboard worked fine, whenever I touched the starter button, the starter motor hesitated at first then sped up. We checked the batteries and found that they were eight years old, so we decided to replace the type 27 starting battery and the large house battery. These were hooked in parallel and had individual on/off switches.

We installed two dual-purpose type 27 batteries, also in parallel, but the starter motor continued to hesitate and then sped up again to start the engine. There were also one or two times when nothing happened at all when we pressed the button. Finally my partner saw a flash in the vicinity of the battery ground and the engine. We sprayed some electrical contact cleaner on the ground connection, and when we pressed the stater button again the starter motor had no hesitation and the engine started up quickly. Since there were no additional sparks or flashes, we don't know what caused the flash. Could it be a loose ground cable, or is there something else we need to troubleshoot?"

Nigel Calder replies:

I'd say it's that pesky ground strap. If corrosion is allowed to occur at the point where the ground strap attaches to the engine block, that will almost certainly lead to starting problems of the sort you experienced. No matter how hard that strap may be to access, you must remove it and clean its terminal and the mating surface opposite it on the engine block. Use fine-grit wet and dry sandpaper or something similar. After you have reattached the connection, give it a good shot of corrosion inhibitor or slather it with Vaseline. That should keep you cranking happily for several years. Inspect the connection visually at least every six months to make sure its performance is not being degraded again by corrosion.

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