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Recently, a Mazda3 turned up at the forecourt but had to wait for a turn at the pumps because we were quite busy. I walked past just as the driver pulled forward to take his place and noticed that the car seemed to judder just as he dropped the clutch. When the young man saw me, he remarked that this happened all the time, but he had to live with it for now because he couldn’t afford a new clutch.
I invited him to the office and explained that it may not be the clutch. I offered to give him a free diagnosis and asked Hennie to investigate. He was back shortly afterwards with the cryptic verdict: “You’ve got an oil leak.”
I knew what he meant but the client, who was called Spencer, was mystified. Hennie laughed and explained that one of the oil-filled engine mountings was leaking and this meant all three had to
Spencer found this statement even more mystifying. “Why would there be oil inside an engine mounting? And why not just replace the one that’s broken?”
It was my turn to explain: engine mountings have to keep the engine/gearbox unit in place so that it cannot shift much during acceleration, braking and cornering. They also isolate the frame/body unit from most of the vibrations created by the engine, as well as isolate the engine/gearbox unit from vibrations caused by suspension movement and
This means that a mounting has to be both as stiff and flexible as possible to dampen any irritating vibration. Rubber compounds cannot deal with these two extremes and this has led to the development of liquid-filled mountings that are able to get closer to the above ideal. However, they tend to leak when they get old.
Signs of a failed engine mounting include visible cracks and separations in the rubber and leaking liquid. If one or more mountings are inactive, this normally causes a violent snatch when engaging gear or accelerating.
A good test for the condition of the mountings would be to get somebody to start the engine, engage first gear and blip the engine to 2 000 r/min and back to idle with his foot on the brake pedal to keep the car stationary. If the mountings need replacement, the engine will tilt excessively to one side. Repeat the test in reverse and the amount of tilt should be about the same in the opposite direction, but keep in mind that a small amount of tilt is normal.