Hey guys, thanks for all the responses.
not to discredit any responses.. but i was searching a little more outside rr.net and found this from honda-acura.net forum. its quoted below. i hope this doesnt violate any copying/quoting rules, mods please delete if so. ill try and verify this too. any other thoughts?...
thanks!
Originally posted by Eric J
All mineral oils are produced from the same basic petroleum feedstocks. Different oil viscosities will not separate or react negatively to each other because the base oil is molecularly the same. It's the different oil additive systems between brands that shouldn't be mixed - if you're concerned about the oil performing exactly how it was designed.
Oil additives include:
Anti-oxidants to prevent thickening at high operating temperatures.
Pour point depressants which lower the temperature of wax coagulation
alkaline materials to neutralize acids formed during combustion.
Rust and corrosion inhibitors.
Detergents to reduce sludge and varnish.
Dispersant additives to hold contaminants in suspension.
Extreme pressure additives to prevent metal to metal contact under high loads.
Viscosity index improvers in formulating muilt-grade (viscosity) oils.
The exact type and amount of these additives varies between brands and when mixed may not function as efficiently as desired. Different viscosities of the same brand oil will have different amounts of viscosity index improvers (polymers), but otherwise the additive systems will be the same.
From the Chevron.com site:
"Can I mix different viscosity grades of motor oils?"
"Yes. It is always advisable to not mix motor oil brands, however, different viscosity grades of the same brand motor oil are compatible. Be aware that mixing viscosity grades will turn out a product that is different in viscosity than either what was originally in the engine or what was added."
From Shell.ca:
"If you mix viscosity grades such as a 5W30 low-viscosity oil and a 10W40 higher-viscosity oil, it is reasonable to expect that the resulting product will have viscosity characteristics which are thicker than the 5W30, but thinner than the 10W40. This change does not reflect incompatibility - it's simply a re-balancing of the viscosity characteristics. In all other ways, the product should work as expected. But there's absolutely no danger about incompatibility resulting from mixing engine oils," Miller says. "We've tested all of our grades and brands, and we haven't observed any problems."
From Mobil1.com:
"For our customers to choose a viscosity grade, we recommend they follow the engine manufacturer's recommendations as indicated in their owner's manual. There is no need to mix two Mobil 1 viscosity grades when one will do; however, we see no problem mixing different SAE grades of Mobil 1 Tri-Synthetic series motor oils."
I agree that mixing oil viscosities isn't really necessary though. 5W-30 is going to have the same viscosity as 10W-30 when the oil is hot... might as well just use 5W-30 for its cold temperature "flowability". So the viscosity mixing argument is kind of pointless
