Mixing oils - good or bad?
Discussion
Chaps,
Quickie.
I have a half-empty can of oil, and a new can of a different brand of oil. Both semi-synthetic, both of the same grade (10W40), both reach the same specification in terms of manufacturers ratings and so on.
I need to do an oil change on my car (8v Mk2 Golf GTi). Can I mix these two oils when I refill the engine? Is it a really bad idea, or will they work quite happily when together in the sump?
Oli.
P.S. Posted also in "General Gassing."
Quickie.
I have a half-empty can of oil, and a new can of a different brand of oil. Both semi-synthetic, both of the same grade (10W40), both reach the same specification in terms of manufacturers ratings and so on.
I need to do an oil change on my car (8v Mk2 Golf GTi). Can I mix these two oils when I refill the engine? Is it a really bad idea, or will they work quite happily when together in the sump?
Oli.
P.S. Posted also in "General Gassing."
Some say "no" some say "why not if they're the same spec"
Personally, I'd stay safe and only replace like with like (but even with a complete oil change you will not remove all the old oil).
Semi synthetic in a MkII Golf?? I'd stick to the ordinary stuff myelf and save the cash. An old motor like that doesn't need it unless you've seriously uprated the performance (i.e.. turbo'd it)
Personally, I'd stay safe and only replace like with like (but even with a complete oil change you will not remove all the old oil).
Semi synthetic in a MkII Golf?? I'd stick to the ordinary stuff myelf and save the cash. An old motor like that doesn't need it unless you've seriously uprated the performance (i.e.. turbo'd it)
Thanks.
I was planning to mix the two, but given that I can get the semi-stuff cheap, I'll carry on using it. It has been running on this for the last 125K miles, and still is as sweet as, and I don't want to risk it.
And anyway, don't be rude about my "Old Motah"! It may be old, but it's still faster than a pedal bike (which is the alternative!)
Oli.
I was planning to mix the two, but given that I can get the semi-stuff cheap, I'll carry on using it. It has been running on this for the last 125K miles, and still is as sweet as, and I don't want to risk it.
And anyway, don't be rude about my "Old Motah"! It may be old, but it's still faster than a pedal bike (which is the alternative!)
Oli.
In the old days you could not mix Synthetic and natural oil. Now they make synthetic from different stuff and so you can mix all you like.
Synthetic contains more cleaning agents and so if you put this in an old engine you will find it will slug up fast.
The e.g 10-50 rating depends on how think the oil is when it is cold and then hot. There are polymers (I think its polymers) that uncurl and curl up when heated and cooled that keep the oil at a stated thickness. If you mix two oils then the amount of polymers will change and so the think ness over temperature.
In short is dose not make much difference unless you are leaving the oil in a long time or racing?
Synthetic contains more cleaning agents and so if you put this in an old engine you will find it will slug up fast.
The e.g 10-50 rating depends on how think the oil is when it is cold and then hot. There are polymers (I think its polymers) that uncurl and curl up when heated and cooled that keep the oil at a stated thickness. If you mix two oils then the amount of polymers will change and so the think ness over temperature.
In short is dose not make much difference unless you are leaving the oil in a long time or racing?
my MKII Golf gets B&Q's finest 20/50 every 6000 miles and is doing fine!!! I save the good stuff for the Tuscan 
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