The same API grade of synthetic motor oil and mineral based motor oil will mix but you will lose the performance of the synthetic oil. However, if a typical synthetic turbine oil is mixed with mineral hydraulic oil deposits may form and with so many different types of oils it is easier to say they don’t mix than to list which types do. And that’s probably how the myth that you must not mix synthetic with mineral propagates.
If they both feel slippy slidy on your fingers then they're both proper oil, so should be fine. (Don't use KY jelly as it's water based)
Christ on a bike, if you buy 5ltr of oil, any oil, you'll have enough to fill the engine and some left over for top ups, you'll know what's in it because you're still using the same tin. When it's empty its time to change the oil and start again
The title of the thread is ‘Does it matter if you mix engine oils?’ It is a myth that you cannot mix synthetic engine oil with mineral engine oil – is that better?
Not quite true...I've got two 5l tins on the shelf...one from Morris...one from Halfords... One of them proved to be too thin when hot and made the oil light flicker at tick over and I replaced it with the other....which was OK. I can't remember which way round it was now Daren't ask on here for fear of ridicule...I'll ask at TE next week, I can handle ridicule better when I'm bladdered
Possibly the Morris is SAE 30, the Halfords a 20w-50 multi-grade? Read what it says on the can and use the multi-grade.
That's good advice but ... since getting the Scooby I have never topped it up (literally) because it never loses oil. So I have a litre or so of Castrol 15/40 and a new 5 litre can of Mobil 15/40. From the advice on here I can go ahead and use both in the oil change I'm doing today. Thanks for all the advice.
I know they separate ...i have mixed the two oils together in a container ....leave it for a bit and they separate . Don't know if it matters , they clearly don't like each other .
The reason i mixed the 2 together was to see what would happen with a synthetic Shell Dentax W diff oil with a 140 mineral which is thick as treacle ...to go into my diff in my 1967 Foden artic unit . It had the synthetic oil in , but the type no longer available . So i flushed it all out and put the mineral oil in , Fodens used the synth as it was less lightly to over heat , but a awful lot of hauliers went back to mineral because of the constant oil leaks via the axle oil seals contaminating the brakes . Interestingly on old lorries left in scrap yards or where ever , it was noted that the diffs in the ones that had synthetic oil corroded and attracted water , but ones that had the mineral in were as good as the day they parked up
the SAE/API bit doesn't mean anything really just a recognised measuring system by a particular body, on the container of oil it generally says sae 20/30 etc, the 20/30 is the spec, surely
