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a debate here at work...
Posted 27 April 2005 - 01:22 PM
Posted 27 April 2005 - 01:40 PM
Posted 27 April 2005 - 01:45 PM
I talked to a friend of mine this past weekend about that very subject - he worked for over 30 years at Mobil Oil and still does consulting work for them (now retired)
Ive heard it doesnt hurt to mix different wieghts, so long as you do not mix synthetic with conventional oil.
Apparently it was a problem in the 70's to mix the early synthetics and conventional oils because there were a lot of esters in the synthetic oils, that would gell into a big ball of goo in the oil pan. - so it was true 30 years ago that you could not mix natural and synthetic oils....
With today's newer synthetics, that is not an issue as there are not much esters in them, in fact I use Castrol SyntheticBlend for my oil, have done so for over 20k, and had no ill affects.
Mixing between brands should not be a problem, but you are going to deal with the effects of cheap oil if you put cheap oil in (ie gelling).
Mixing viscosities should not be a problem either - I do it frequently when topping off, and have had no ill effects.
Posted 27 April 2005 - 02:23 PM
As to grade mixing. The viscosity rating for 10-30 means 10 weight viscosity at low temperature, 30 at high temperature. If I recall its at the freezing and boiling point of water. The SAE ratings do not specify how it gets there. So some oils have a straight line relationship between weight and temperature through these points, others are more curved. Also, the behavior beyond those points is not always on the same trend. This means if you blend in different ratios, with different manufacturers you can have different perfomance.
As was stated earler most modern oils are pretty good and very shear resistant through a broad temperature range. Especially the synthetics. In the past sometimes the lighter blend would consume at a faster rate than the heavier. I don't know if this is still the case but I just stay away from blending unless its an emergency.
Posted 27 April 2005 - 03:14 PM
Should you? No. They make every weight you'd ever need; pick one. Every company has its own formula. It's not just raw oil in there. Lots of other crap is blended in. Again; pick one.
Posted 27 April 2005 - 04:03 PM
It's the weights that could cause a problem not the additives.
Although in a pinch, I'd mix weights & brands rather than run it low.
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