Dear Tom and Ray:

I am really bad at keeping up with timely oil changes on my 2005 Ford Windstar. When I do change the oil and filter, I write the date and the odometer mileage on the side of the oil filter. The last time I changed the oil, I had gone 13 months and 10,000 miles since the previous change. To make up for my lack of timeliness, I drain the oil out of the engine, pour a gallon of diesel fuel into the crankcase, start it up and let it idle for five minutes. I then shut it off, drain it again, replace the oil filter and add new oil. I have been doing this for the past 100,000 miles, and the engine still runs great, with no leaks or burning oil. Is flushing the engine like this OK, or am I eventually going to trash it?

-- Paul

TOM: Gee, I was about to tell you to stop this immediately. Then I got to the part about 100,000 miles without burning or leaking oil, and I ran right out to try it on my car!

RAY: And now his car is the world's largest Italian-made paperweight.

TOM: Actually, it is a testament to how well-built your engine is, Paul, and how good modern oils really are, that you've had no damage to date.

RAY: Everything we know about engines and lubrication suggests that you should be doing serious harm. Engines have metal parts that rub against each another continuously. The piston rings rub against the cylinder walls; the connecting rod bearings rub against the crankshaft journals.

TOM: To keep these parts from destroying each other, engine manufacturers have spent untold millions of dollars devising sophisticated oils and lubrication systems. If something as simple as flushing the engine with diesel fuel added to an engine's longevity, I'm sure manufacturers would have recommended it years ago. Remember, they're the folks who pay the warranty claims, so they have a financial interest in keeping your engine running.

RAY: At least until the warranty's up!

TOM: The truth is, any liquid can be used as a lubricant. You can put water or eggnog in your engine, and it will provide some degree of lubrication -- more than nothing. But it's not as good as motor oil. And neither is diesel fuel -- especially the newer diesel fuel, without sulfur. And when you're dealing with parts as expensive as internal engine components, why would you ever risk damaging them?

RAY: So I'd have to conclude that you've been phenomenally lucky, Paul. You clearly have led an exemplary life. And I have to assume that the reason you've neglected your oil changes is that you've been in Calcutta, filling in for Mother Teresa.

TOM: But like all people who've gotten by on luck, it's going to run out at some point. I think sooner rather than later.

RAY: So we want to advise all of our readers to be careful about purchasing any '05 Windstar next week from a guy named Paul. Or a guy with a heavy beard who calls himself Mother Teresa.

TOM: My advice would be to simply skip the "flushing" step when you change your oil, Paul. Even if you've waited too long between changes, whatever damage you've done by then is done. The best thing you can do is simply change the oil and filter. Or if itreally been a long time, change it, drive for a week and then change it again.

RAY: Or, if you know you're not good about changing the oil, switch over to a synthetic oil, which costs more but lasts longer, and gives you more time to perform your saintly duties between oil changes.