There was an article in ?Car Mechanics? recently. I?ve asked them and they say I can reproduce part of it here for us.
There is a certain pride in maintaining your own car, partly stemming from saving money but also from gaining satisfaction in the knowledge that you?ve just sorted a job out by yourself. A feeling of independence.
This helps to explain why a friend of mine insists on dealing with the mechanics of every car in his family, and there are several.
He is pretty well equipped as he runs a Triumph Stag. If ever a car needed vast amounts of skill and tender loving care to run at an acceptable level of reliability then it is the Stag. Suffice it to say that this fella is pretty handy with the spanners.
Another car in his family?s stable is a VW Passat and it began to play up.
The problem was a distinct loss of power either when the engine was cold, or at high speed.
He did all of the things that most of us would, such as check the air filter, fit new plugs and HT leads and look for faults in the fuel system. It was all to no avail.
It was suggested that the ECU was to blame and, as you will know, this item is far too expensive to replace in the vague hope that it could be at fault.
He did the wise thing and borrowed one to try out. No joy.
By now, he had to admit defeat and call in the cavalry. Or, rather, take the VW to the cavalry, in the shape of the main dealer.
The car was run up on the diagnostic machine but the operator couldn?t pinpoint the problem. Off it went to another main dealer, with the same result.
The third port of call was to an emporium which was both humble and unpromising. A 2-man band up a back street whose charm was born more out of quaintness than apparent efficiency.
The guys who ran it, although not exactly into space-age technology, did possess a diagnostic machine and it was with the help of this that they sorted the Passat.
I don?t know what sort of machine it was, but it was able to tell these guys that the valve clearances were not correct at certain times, probably detectable by the compression readings.
They noticed this fault and let logic come into play. The clearances were too wide when the engine was cold and at high revs. In other words, the oil was either at its thickest or was being pumped around vigorously.
This model of Passat has hydraulic tappets and it occurred to these guys that they were being pumped up too far, which meant in turn, that the valves were not being allowed to seat properly.
It then occurred to them that the only thing that could have a bearing on the matter was the pressure release valve on the oil pump. And, indeed, it transpired that the valve was sticking.
Rather than mess around, they fitted a new pump and the problem was solved.
I am still a little baffled because, in my experience, hydraulic tappets have drain holes which are designed to overcome a problem of excess pressure. This must not be the case with the VW.
Whatever the case, I can say in all honesty that I would never, ever have got to the root cause of the VW?s loss of power. Not with a diagnostic machine, not with a crystal ball and not with the help of Merlin.
Would you?
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Sean,
I conclude we need oil pressure guages on hydralic tappet engines.
This will give you over pressure at cold and over pressure at high speed.
But who will understand this rare condition when sitting in the driving seat?
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