Engine flushing

A subject that's been getting more attention these days is internal engine cleaning or flushing. This is being promoted by the quick-oil-change people, among others, with the advice that if you clean out the engine of accumulated sludge, deposits and other disgusting stuff, it will run better and hopefully longer. Is this effective or not? As usual, when it comes to things automotive, the answer is both yes and no.

If you've seen some of my columns on oil and oil changes, you'll know that unless the oil is changed frequently, not only will the oil's "oiliness" go away, but varnish and other compounds will form inside the engine. These get deposited at various places including the small oil galleys (passages) and begin to restrict oil flow-much in the way that cholesterol blocks flow in a biological system.

Personally, I consider engine flushes a waste of money, but they can be beneficial. For example, an engine flush might be useful in a relatively low mileage car with 30,000 to 40,000 miles that hasn't had its oil changed as often as it should have been. Such a car may be an off-lease car. At this point, cleaning the engines innards may prove to be beneficial because sludge and varnish buildup may not be that bad yet. Notice how many times the word "may" is used here-you can't really know for sure without taking the engine apart.

You may be able to get an idea of what the inside of the engine looks like if you're able to remove a valve cover. On some engines, where there aren't tons of hoses, lines and other things covering it, it's all a matter of removing a few bolts. A clean engine will not have any encrusted deposits on the cover or any other deposits on the cylinder heads. I've seen engines where there's been so much coking (crusty deposits) that after the valve cover has been removed, a perfect mold of the cover (writing and all) has been formed on top the cylinder head so it looks like the valve cover hasn't been removed at all! I've also seen engines that, after the intake manifold has been removed (on a V-8), all you see is a huge mass of black carbon in the lifter valley. I'm always amazed that such engines still run.

On a badly maintained engine, there are probably already too many deposits for the flushing chemicals to completely remove. But the real danger here is that the chemicals will dislodge enough crud that it will block the very small passages in hydraulic lifters or even clog up the fine mesh oil pump pickup screens. On such engines, you're better off changing the oil frequently, say every 2,000 miles, so that the natural cleaning properties of the oil will somewhat reduce accumulated deposits.

If you insist on engine flushing, try this method. First, change the oil and filter and on a five-quart capacity system. Fill the engine with 4-1/2 quarts of 10W oil and a half quart of kerosene. Turn the engine on and let it run by itself for 10 minutes or so. Don't rev the engine! The drained oil should be quite dirty. Change oil and filter once again, with a regular grade of oil. This is a relatively mild cleaning but if your engine is really dirty, it's only a matter of time before it gives up the ghost.

[Peter C. Sessler has written over 30 automotive books. Besides books, he also writes for several Internet web sites and car magazines. He has also written (with his wife) a children's six-book series on auto racing. His latest books include "Camaro Photo Archive," "Jeep Prototypes and Concept Cars," "The Ultimate American V-8 Engine Data Guide" and "SVT Mustang Cobra Recognition Guide, 1993-2000."]