Dear Ole Mechanic:

I read your column some time back about the person that had gasoline put in the tank of his diesel truck.  I accidentally put diesel fuel in my wife’s gasoline car.  Fortunately, the station cashier ask me if I had a diesel car, as that is what I had put in it.  I did not start the car but had it towed to a nearby small independent repair shop.  The repairman simply siphoned as much fuel out of the tank as he could.  Then, he put ten gallons of gasoline in it and told me to go back to the station and finish filling it with the super-premium grade of gas.  I was worried but did as he said.  The car has run fine since, but I am worried that I might have hurt something.  Did I?  Thank You.Diesel Fuel Pump

Feeling Stupid


Dear Feeling;

I know the feeling stupid part, but I was lucky.  When I grabbed the diesel hose and punched the Regular button on the pump, the pump wouldn’t come on.  Even if it had, I wouldn’t gotten too far.  You see, I am surprised that you didn’t notice the green hose or the fact that the nozzle did not fit into the smaller fuel-filler opening in the gas tank of your car.  That should have been your first two clues that something was not right.  The smaller hole, also known as a restrictor, is in the filler-neck of the tank for a purpose.  It is to try to prevent you from putting in leaded gasoline, which should have a nozzle larger than the small hole.  This was done to prevent leaded gasoline from being put in the car, as leaded gas would damage the catalytic converter.  While leaded gas is now just a distant memory, the diesel nozzle is even larger than the leaded-fuel nozzle.  I suppose that the station could have had a small nozzle on their diesel pump while their diesel nozzle was being repaired, but they better not get caught, as there is a hefty fine for that.

The repairman or mechanic did the correct thing even though it was a short cut and cost you--I hope--a lot less than the "correct" repair.  The “factory-recommended” way to correct your problem would be to completely drain the gas tank by removing the gas tank and cleaning it, which would be a real hassle and expensive.  But it would be exactly what a dealership should do to avoid any liability for damage to any “Emission” part.  Your small independent repairman did just fine!  By removing as much diesel fuel as possible and then diluting what was left as much as possible the diesel that was left probably amounted to the equivalent of putting in a couple of containers of aftermarket upper-cylinder lubricant.  The small amount of diesel left in the tank would have been diluted to the point that none of the emission parts like the catalytic-converter would have been hurt.  It might be advisable to have the fuel filter changed sometime in the near future. The next time you have the oil changed would be fine, but there isn't any hurry.  That is,  unless the car seems sluggish, is knocking or making noise. However, you said that it was running fine.  Some might suggest that you use a fuel-injector cleaner additive, but I suspect that the diesel fuel cleaned them up just fine.  Don’t get me wrong; I do not recommend using diesel fuel as an additive to gasoline.  Most of today’s gas additives are more refined than diesel fuel; although, some upper-cylinder lubricant additives are somewhat close to diesel fuel.  The reason that the repairman told you to fill up with super-premium gasoline was to offset the very-low octane-rating of the diesel fuel. 

Had you run the car with mostly diesel fuel, you could have damaged the catalytic -onverter due to the heavy unburned hydrocarbons coating the catalysis.  If a gasoline engine is warmed up and there is some gasoline mixed in with the diesel fuel, the car may start and at least try to run.  It wouldn’t be pretty due to the massive clouds of smoke from the tail pipe and the rattling and banging from the engine.  If it did run very long, there could be some serious internal engine damage.  Since you did not start the car and followed the mechanic's instructions, you probably didn’t hurt your car at all.  It sounds like you "lucked out" and found a good independent mechanic.  If he is located nearby, you might want to at least visit with him about any future repair work.

Herr Professor Nuzanbolts