Piston Slap: Diplomatic Immunity

Sajeev Mehta
by Sajeev Mehta
piston slap diplomatic immunity

TTAC Commentator ajla writes:

Hi Sajeev, I recently overpaid on my purchase of a 1986 Dodge Diplomat SE in order to save the car from meeting a grim end in the Cash 4 Clunkers program. The car is in good shape and has 98,xxx miles on the odometer. My question is this: The Diplomat has a 2bbl 318 V8, but every single gas station in my part of Florida only sells E10 fuel. I’ve read that running E10 in a carbureted engine can cause some big problems. If this is true, what kind of trouble should I be expecting, is there anything I can do to mitigate the negative effects of E10, and how long do you think I have until issues start to crop up? Would I be better off just searching out a station that sells pure gasoline even if it’s fairly far away?

Sajeev replies:

And kudos to you for saving a cool car from the C4C program! While it took me about 25 years to consider these final “Dippys” worth more than scrap, I was wrong. No matter how out of touch the Diplomat was to the imports or the freshly minted Taurus, it will never meet the historical fate of the Chrysler Sebring. Ever.

That’s a cool car, much like my 1972 Continental Mark IV. Whose 4bbl Holley operates well on E10 gas. For the past three years, in a hot climate similar to Florida.

So, while E10 definitely sucks, it won’t kill your car. The Mark IV sits for months waiting for the Mehta brothers to pimp the streets of Houston in style, but it never complains. Starts in about two milliseconds, idles great, etc. While your carb is “choked” (get it?) by electronic engine control add-ons, I suspect a full rebuild with new springs and rubber is what you’ll need if performance becomes a concern.

I’ve heard that older cars (and lawn care equipment) benefit from an occasional bottle of fuel system cleaner to proactively treat E10’s side effects: ruining rubber seals, clogging little passageways, etc. That makes sense, and fuel system cleaners are cheap. I’ll occasionally throw a can of Sea Foam in tank for this reason, especially if the car stumbles or stalls when it shouldn’t.

[Send your queries to mehta@ttac.com]

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2 of 27 comments
  • Nikita Nikita on Oct 20, 2009

    TZ: Many places E10 is mandatory in all grades. We have an '86 Dodge Ram Van with the same 318 2-BBL and it starts and runs fine on E10. Those engines have an O2 sensor, computer and electric variable jet in the carb to vary the mixture. The only thing necessary for it to "wake it up" is just advance the timing a few degrees.

  • Armadamaster Armadamaster on Oct 25, 2009

    Nice save, had a 1985 Diplomat stripped not equipped and I still miss that car from time to time. Wish I had a building to hide another one in for weekends.

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