My ears perked up when I saw your posts on the hard starting problems you were having especially when things started revolving around alternators and especially when TWO were found to be faulty. This can be a pretty difficult thing to truly diagnose. The obvious conclusion when the battery drains but is a good battery would be a bad alternator. But when that is replaced and symptom still exists, then another alt is put in and problems persist, it is likely there is another cause for the problem.

A faulty glow plug relay will cause the glow plugs to stay on for longer than their 2 minute cycle time or it can come on also while driving, something that you can’t tell is happening.and because glow plugs draw more amperage than the alt can put out, the battery will drain. Cold weather just exacerbates the problem. Add injection line heaters, 8 amps or more is added to the already “draining faster” electrical system.

One way to tell if your glow plug relay is coming on when it’s not supposed to and draining your battery is to connect a 12 volt light to the glow plug fuse and ground it to the body. Use enough wire so you can place it in view, inside the car. Start and run, the light should be on when you start and 120 seconds or so later go off. If it come back on while driving, you have a faulty glow plug relay and it will need to be replaced with a properly functioning one.

I’m on my fifth veg oil powered Mercedes and while I haven’t experienced every last conceivable weird out…I had my share – and share I will – my experiences as they occur and hope it helps out one of my fellow vegcar pals out there.

–240D Rich

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