An engine has an oil capacity in the book, and the drain trolley under the ramp has a graduated tank, and the two agree to a cupful on every car I do. This one drains six point one litres from a sump that holds four point three, every year, and the dipstick was on the line before I pulled the plug.
I do servicing at an independent garage, and the oil is the part of the job nobody thinks about, which is why I do.
How the numbers work.
The book gives the capacity with a filter change. The drain trolley has a graduated tank, so I can see what came out. The dipstick has a minimum and a maximum and the gap between them is about a litre. On a car that has been run and stood ten minutes, the sump drains what the book says, less a couple of hundred millilitres that clings, and I refill to the book and the stick reads full.
That agreement is not a coincidence. It is the engine being a fixed size.
One car, a small estate with an engine the book says holds four point three litres, drains six point one.
Every service. Dipstick on the full line before I start, so it is not overfilled. Plug out, six point one in the trolley, and the trolley's graduations are checked against a measuring jug because I did not believe it the first time.
Six point one is not a sump. It is a sump and most of another one. The engine is not big enough to hold it: the pan, the galleries, the filter and the head together come to four point three, which is why the book says four point three.
And it is not a slow drain from somewhere else. It comes out in one flow, warm, the colour of used oil, in the time a sump takes to empty, and it stops.
What has been checked.
The trolley, against a jug, three times. The jug, against a second jug.
The engine number. In case it is a bigger engine than the book thinks. It is the engine the book thinks, and I have looked at the sump, and it is that sump.
The refill. I put in four point three and the stick reads full. Not overfull: full. A year later, with the car having done its ordinary seven thousand miles, the stick reads full, and it drains six point one.
Consumption. If the engine were somehow making oil rather than burning it, the level would rise over the year and it does not. Full going in, full a year later, six point one coming out.
I have drained it into two separate containers, four point three in the first and the rest in the second, to see whether the last litre and a bit is different.
It is the same oil. Same colour, same smell, same grade by the feel of it, and the supplier's lab, which I sent a sample of the second container to, says it is the oil I put in, with a year's use on it.
The weight.
This is where I stopped telling the lads about it.
I weighed the car on the weighbridge at the scrapyard, on the way in for a service, with a full tank and the oil at the full line. Then I drained it, six point one litres, and drove it round the block to the weighbridge before refilling, on the last of what was in the galleries.
It weighed the same. To the ten kilos the weighbridge reads in, a car with six point one litres of oil in it and a car with none weighed the same, and six litres of oil is over five kilos, and a weighbridge that reads to ten would not see five, so I am aware that proves nothing, and I am also aware that I did it.
What is done about it.
The car is serviced, the oil is changed, the stick reads full, and the extra goes in the waste oil tank with everything else, and the waste oil contractor pays us by the litre, so in a small way the car is a source of income.
The customer does not know. It is a reliable car and he is a reliable customer.
What I do.
I do the services.
The one thing I have changed is that I drain it with the trolley's lid on.
The trolley has a funnel top that you leave open, because you want to see the flow, and I used to watch this one because I wanted to see where the extra came from.
In 2023 I watched the flow from the plug hole run down to a drip, at about four point three by the graduations, the way a sump does, and stop. And then it started again. From an empty hole, in a drained sump, with the engine cold and the car still, a second flow, steady, warm, for the time it takes to drain a litre and three quarters, and I did not put my hand under it, and I put the lid on the trolley, and I have kept it on since.