Well it all started last summer when all of a sudden I noticed that the oil level needed topping-up – regularly. By December’s 5k oil change I topped-up over 1L.
It was then that I spotted an oil leak from the rear of the driver’s-side cam cover. I obviously assumed this was the reason for the oil loss, so bought the bits and in April this year had the gasket changed. I checked the passenger-side cover as well, but as it seemed dry all around I did not change it.
However the oil loss did not stop… over the past 2.5k miles since April I already added 3/4L of oil.
The car was due for the summer 5k oil change, so today I had a good look all around and under the engine bay. There is absolutely no sign of a leak anywhere, both cam covers are dry, as well the underside and the sump.
The two sources of hidden oil leaks that I could think of are the oil cooler and the rear crank seal. The coolant does not seem to have any oil in it (I changed it today, so I know…), but I have no easy way of finding-out if the rear crank oil seal is leaking into the torque converter so this remains a theoretical possibility.
Then something else occurred to me – the car was always getting semi-synth 10W-40, until last year’s summer oil change which was done by Vx who decided to ‘surprise’ me with Mobil-S full-synth 5W-40, and at the December oil change I used Mobil-1 full-synth 0W-40. So this got me thinking – is the missing oil problem related to the use of full-synth?
Well it wouldn’t be that old problem of oil leaks developing when swapping from mineral or semi-synth to full-synth, because there is apparently no oil leak in the first place… but what if the 5W and 0W viscosities are too thin for the engine when cold, and it then consumes some oil until it warms up? But if this is the case then this should also be applicable to Vx full-synth oil which is 5W-30…
So I think this a bit farfetched, but to test this theory I used for today’s oil change Vx’s good old semi-synth 10W-40, and will report back in a couple of thousand miles to let you know what happened.
Incidentally, I agree with Mark DTM who made a comment that an engine that consumes some oil is a good thing, as it provides good lubrication for the piston rings. But the point is that I can’t afford to feed it with the very expensive Mobil-1 diet, so even if it continues to need topping-up then at least I will be using Vx low-cost oil… and I still don't understand how from not consuming any noticeable amount of oil it turned over-night to an oil drinker.
Also, on the issue of oil costs, I just came back from Italy where a litre of Mobil-1 0W-40 costs 11.00 Euro (around £7.50), as opposed to the £13.00 it costs at my local Esso garage…
