I too have to wonder why the headgasket? This is not normal maintenance, unless there is a problem. Letting it cool every few hours makes me think you have a cooling issue? Of course this would tie into the headgasket, if in fact the headgasket is the cooling issue.

Having taken long trips on veggie in my truck, I can say getting it working just before a trip spells trouble. Getting good fuel on the road can be a real problem. I carried a 275 gallon tote and pre arranged for clean wvo. Your going to be limited to 20-30 gallons because of weight. 8 pounds per gallon. I am not saying no don't do it, but think it through.

I helped a young couple in Montana with a Dodge on wvo. He was headed for Alabama, or at least trying to. His fuel line had a very small leak just before the filter so was sucking air. Took a bit to find it. It was cold and windy, and the middle of no where. He was happy to load me up on veggie oil for getting him going again.

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1977 240D turbo