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I'm wondering if there's an issue with these old trucks switching to the 10% ethanol / gasoline blends. My understanding is that ethanol's a pretty good solvent, loosening up the 40 yrs of sludge, deposits, and varnish that might have been left alone with pure gasoline but are now becoming partially dissolved and are clogging up our carbs, fuel filters, etc. Maybe also dissolving the rubber flex lines and various gaskets not exactly designed for ethanol.
Does this make it worth having the tanks cleaned out by a radiator shop, flushing out fuel lines, replacing rubber hoses with modern stuff, and throwing in an in-line fuel filter (or two) to supplement the one sitting on the fuel pump? It'll be a little longer before my F100's ready to hit the road...but didn't know if I should add this to my "to do" list.
I know Union 76 has been adding ethanol to their gas for a long time here in California. I haven't seen or heard anything to support your question. But in general terms, I think it would be a good idea to replace the two 12" sections of rubber line at a minimum. If you add a cheapy clear plastic filter under the cab you can atleast see what is being sucked up by the engine and if you have a need to flush your tank. That is what I would do.
I herd the same about the rubber hoses, that the fuel will eat them. It also said that alot of damage can be cauesd to the manual fuel pumps of old rigs. I know that my truck is having fits right now, not sure if this is the problem or not, but will be one of the things that I will be looking into.
Been running the blended fuels in both 65's and have not experienced, or noticed any problems, think Ca. adds couple extra just for good measure. Definately need to install hardened seats when it comes time to rebuild engine. If there is any old stock fuel lines on the truck, certainly would not hirt to replace them. An argument could also be made regarding the engine oil. With tech advance of modern engines, oil manufacturers have been removing, or reducing additives that were beneficial to the early model engines. As airharley suggest, installing a fuel filter is prevent maint. for these vintage truck, and any type inline filter will work, I installed a summit canaster filter on driverside inner fender just before the fuel filter.