Originally Posted by Triple_Se7en
But Yes..... you can even blend 20w50 with 0W20.
It's all compatible..... 15w40, 5w40, 10w50.....etc.... blend away. Even allowances with diesel/gas passenger oils/vehicles.
The miscibility standard is
NOT an endorsement. I know Shannow has painstakingly delved into this multiple times and I'm not willing to give it the same effort, but if you mix (not blend, a blend is produced by a chemist or tribologist with full understanding of the variables involved and with testing of the final product) two oils together the standard, which is based on a pre-selected panel of test oils, is designed to ensure that the resultant product doesn't split or gel. There is absolutely no attention given to the performance of the resultant product. Any approvals that the former individual constituents held are now wholly invalid, as it was only the fully formulated product, as blended by the manufacturer, that passed the requirements for those approvals. The Winter rating may have slipped, as this is the most likely casualty from mixing oils with different bases, different PPD's and different additive packages.
All that said, the OP is mixing two oils from the same manufacturer and product line, so they are likely formulated quite similarly and I doubt there will be any adverse effects from putting them together to use up the product he hadn't meant to end up with.
It doesn't matter that Fred's uncle Billy has been mixing Quaker State with the 50 gallon drum of 1950's Valvoline HD30 that he picked up at a yard sale for $20 10 years ago and his 1963 Massey-Fergusson is "smooth and quiet" or "hasn't blown up yet". Absence of failure is not proof of performance and neither are personal anecdotes based on subjective observations like "smooth" and "quiet" or "peppier" or any other metric that lacks any sort of formal qualification properly measured with the appropriate hardware.
Pennzoil on switching back and forth between conventional and synthetic:
Originally Posted by Pennzoil
It is advisable that you use the same oil for top-ups if needed, thereby giving you the best protection from the oil that you have chosen.
Pennzoil on using additives:
Originally Posted by Pennzoil
No. High-quality motor oils, such as Pennzoil® brand products, already contain carefully balanced additives for optimal performance.
Amsoil:
Originally Posted by Amsoil
While it's safe to top-off an engine that normally uses AMSOIL synthetic motor oil with conventional oil, we recommend changing the oil at your earliest convenience. In fact, AMSOIL does not support extended drain intervals where oils have been mixed.
Mobil:
Originally Posted by Mobil
In general, oils should be compatible with each other. It is not likely that you would form gel by mixing the two oils. However, we would not recommend mixing oils as a general practice because oils are complex mixtures of additives and base oils that can be destabilized.
Motul:
Originally Posted by Motul
Motul® SYNTHETICS CAN (if you cannot find your brand) be mixed with MOST high quality mineral, Group 3, PAO or ESTER synthetic oils, without major problems. Try to stay close to the viscosity range. (I.e. 10w40 mixed with 10w40). If you have mixed oils, Motul® recommends an oil change when you get home from a "long" trip that has consumed the oil, since the oil additive and base from our oil is now not balanced.
Castrol (from
THIS thread):
Originally Posted by Castrol
- For topping off: You can use any of their products / formulations so long as it is the same grade. They do not recommend topping off with another grade.
- They do not recommend topping off with a different formulation on a continuing basis.
- Do not recommend mixing different grades even in the same formulation.
- Do not recommend mixing formulations due to changes in viscosity that can develop.
