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Engine Flushing - Does It Work?

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On: Sat, Sep 3, 2011 at 8:48AM | By: Peter C Sessler

Engine Flushing - Does It Work?

This subject has been getting more and more attention these days—it is internal engine cleaning, better known as 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 yucky 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 know cars and engines, you’ll know that unless the oil is changed frequently, not only will the oil’s “oiliness” will 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 arterial flow in human beings.

Personally, I consider engine flushes a waste of money, but they can be beneficial, in certain limited situations. For example, an engine flush might be useful in a relatively low mileage car with 30,000-40,000 miles that hasn’t had its oil changed as often as it should have been—for example, 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 engine looks like inside if you’re able to remove a valve cover. On some engines, where there aren’t tons of hoses, lines, and other things over it, it’s all a matter of removing a few bolts. A clean engine will not have any encrusted deposits on the inside 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, that a perfect mold of the valve 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! And I’ve 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. It’s always amazed me 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 that oil pump use on the pickup screens. On such engines, you’re better off changing the oil frequently, say around every 3,000 miles, so that the natural cleaning properties of the oil will reduce, somewhat, accumulated deposits.

If you insist on engine flushing, you can 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 idle 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.

Finally, my mechanic had to replace the valve cover gasket on our 1998 Dodge Caravan (which has 198,000 miles on it). The mechanic was quite surprised when the valve cover came off—there were absolutely no deposits of any kind! The reason, of course, was the use of Mobil 1 synthetic oil, since we bought the van at 65,000 miles. The oil, by the way, has been changed at 12,000-15,000 mile intervals.


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