I notice the question was raised in H.J`s column in this week`s Telegraph about oil changes using a vacuum pump via the dipstick tube, and that H.J. mentioned his dislike of this practice as not all the sludge was being removed from the sump.
Unfortunately to maintain/increase profitability, this practice is now becoming the norm in many main dealerships including BMW.
One can understand the use of this system when diesel engines are encased within sound proofing shrouds, but with an ordinary petrol engine the actual time saving would seem minimal and surely inferior to the traditional method.
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"One can understand the use of this system when diesel engines are encased within sound proofing shrouds, but with an ordinary petrol engine the actual time saving would seem minimal"
Increasingly petrol engines have the same or very similar shrouds and access is just as complicated.
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Should there be any sludge, if the correct quality oil is used? I thought that one of the required properties of an oil was to withstand high temperatures, and to also carry any foreign bodies i.e. sludge, in suspension, through detergent use. If the sump contains sludge, neither sump draining nor vacuum pump from above is going to make a lot of difference, surely?
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I drive a diesel, so the oil gets black pretty soon, I change the fully synthetic every few thousand miles, but I drain in into an old washing up bowl, and leave it until I have time to mess about with a funnel and a container, when I come to put it into containers, it is evident that there is a thin layer on the bottom which is greasier than the oil, it's about 2mm thick and is just like the oil but a bit thicker, not sludge, no bits in it, just carbon that has settled I expect.
Well, I still get this whether I do vacuum changes or drains.
I thick because the bottom of the sump is flat, that much of this deposit would remain anyway and the oil will just drain over the top of it. We are talking about a very minimal film here!
I think if engine manufacturers made the dip stick tube align with a well in the sump, or something like that, the effect of removing heavier deposits woul be better than anything!
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