mixing motor oil

[Erik]

stupid me, went out to buy oil for an oil change and accidently grabbed 2 quarts of 10w-40 royal purple and 5w-30 royal purple. they where stocked behind eachother so i assumed (like an idiot) that the people working at pepboys put it in the right spot. I noticed this half way through putting my 4th quart of oil. basically, do i need to flush the oil out and replace it, or can i run 2 different weights?

[420sx]

Depends how much you care about the car. If i was my daily beater, I'd probably say **** it, and run it. If it were my 240... I'd drain it and try to make pepboys give me new oil.

[DPancoast]

You can mix different grades of oil. I hear you shouldn't mix synthetic and normal oils (unless the synthetic's manufacturer specifically says it's OK).

Some also say that in newer cars, thinner is better because if you run thicker on a NEW car, it can raise oil pressures.... I don't know for sure though.

[Renegade_]

The viscocity of oils change as the temperatures in the engine changes - its fine. Just because an oil says is 10w-30 means it can be anywhere within that range at operating temperatures. It could be 23 weight if you just let it idle for a while...

[OutToWinPAHC]

I don't see an issue really, its not like you mixed 5-20 with 20-50, you will be fine, its the same type and brand of oil with the same chemical additives.

[TROLL]

a simple google search would have returned the info you were looking for:

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.

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."

[Vr-4-Life]

a lot of companies even sell 50-50 oil for a middle price. I have however mixed 5-30 and 10-30 many times in the del sol when running low. Dont do it a lot though.

and that sucks.. royal purple is some expensive stuff good luck getting your money back.

[Erik]

Originally Posted by TROLL

a simple google search would have returned the info you were looking for:

I looked online after posting (sorry troll) and found that exact post on another board. I googled mixing motor oil and didnt find anything about grades, just synthetic/mineral/normal mixtures. I didnt worry about it, and im just going to watch the consistency. Its only a daily driver, no mods except speakers and headunit, so nothing performance wise.

I also called pep boys and bitched about it and they said there is no way to tell if that was our fault or not. they said i could easily just be trying to get 2 quarts of free oil. I told them im not that much of a cheap ass, and continued on my way.

I dont expect to be suffering from much temperature change since i change oil every 2k, it should stay relatively cold during that time period. I drove the car for about 20 minutes and checked the consistency and it feels pretty normal.

[TROLL]

On another note, changing oil every 2k is completely pointless... even 3k is excessive. There is no benefit to that at all, except for you fueling our economy ever so slightly.

[Erik]

Originally Posted by TROLL

On another note, changing oil every 2k is completely pointless... even 3k is excessive. There is no benefit to that at all, except for you fueling our economy ever so slightly.

eh well aware of that. i know oil can last much longer than that, but its just one of those things ive always done. I know it doesnt help much, or even at all, but it sure cant hurt either. im pretty excessive with maintenance.

[Vr-4-Life]

do you burn or leak and oil? just keep in mind you can run royal purple for almost forever but you should ALWAYS make sure you have the correct ammount in over time. I try to check my oil once or twice a week. Ive seen people run synthetic and then 7k miles pass and they go to change it only to find that they are down to almost nothing.

[rich33389]

You now have 7.5w-35 in your car, big deal

[lagos]

Originally Posted by TROLL

On another note, changing oil every 2k is completely pointless... even 3k is excessive. There is no benefit to that at all, except for you fueling our economy ever so slightly.

Remind me to never buy a car from you.

[russiankid]

Originally Posted by rich33389

You now have 7.5w-35 in your car, big deal

How did you calculate this?


I doubt you'll have any mechanical problems just don't do it again.

[Erik]

Originally Posted by Vr-4-Life

do you burn or leak and oil? just keep in mind you can run royal purple for almost forever but you should ALWAYS make sure you have the correct ammount in over time. I try to check my oil once or twice a week. Ive seen people run synthetic and then 7k miles pass and they go to change it only to find that they are down to almost nothing.

I burn about 1/2 to a whole 00 quart over 1500 miles. Its not too much, but i do too check my oil about 1 a week.

Originally Posted by rich33389

You now have 7.5w-35 in your car, big deal

chill dude, its a first for me to accidentally mix oil. id rather be cautious than risking anything internally. enough with the attitude.

Originally Posted by russiankid

How did you calculate this?


I doubt you'll have any mechanical problems just don't do it again.

The calculation is the average of the 2 numbers. 5w/10w=7.5 && 30/40=35. I dont plan on doing this again, lol just a careless mistake on my part.

[russiankid]

Originally Posted by Erik

I burn about 1/2 to a whole 00 quart over 1500 miles. Its not too much, but i do too check my oil about 1 a week.


chill dude, its a first for me to accidentally mix oil. id rather be cautious than risking anything internally. enough with the attitude.


The calculation is the average of the 2 numbers. 5w/10w=7.5 && 30/40=35. I dont plan on doing this again, lol just a careless mistake on my part.

You can't calculate the weight by just adding and dividing. Oil weight is determined by polymer additives. So unless you're a chemist, you won't be able to tell how the different polymers interact.

[Erik]

Originally Posted by russiankid

You can't calculate the weight by just adding and dividing. Oil weight is determined by polymer additives. So unless you're a chemist, you won't be able to tell how the different polymers interact.

i agree, unless its a ridiculous coincidence, which ill bet it isnt. i believe that is how he came to that conclusion.

[lagos]

Just to sum things up. Its not a big deal and wont hurt anything. Dont worry about it.

[Raven18940]

This depends entirely on the engine. My saab loves 40 weight, my jeep develops a rod knock so bad I drained the oil after just 250 miles.

[Erik]

well only time will tell with my situation. sucks a did with royal rurple and not like castrol or somthing a little cheaper. i learned a lesson. ill be checking the oil every few days for a while to make sure the viscosity stays normal