Mixing oil weights and conventional/synthetic

[wolfehunter]

So in preparation of my oil change in my 98 Chevy truck (5.7) I noticed I had 3 quarts of Quaker State Advanced Durability 10-30 in the back of the cabinet. I would like to use it up. Preferred for the truck is 5-30 but manual says 10-30 acceptable if over 0 degrees. I change oil and filter every 7500 or every year whichever comes first and I have a Wix 51036 or a Napa Silver to throw on it....didn't decide.

The oil change calls for 5 quarts of oil with filter change so my question is can I use the 3 quarts of conventional QS 10-30 and add 2 quarts of 0-30 to get me closer to the preferred 5-30? Can I use 2 quarts of synthetic 0-30 to make my own "blend" or is this harmful in any way? The truck has around 116K on it and I was leaning towards going to synthetic for longer oci's. Thanks.

 

[oldhp]

Won't hurt a thing. Either way your fine.

 

[salv]

I'd just buy 2 more quarts of QSAD 10w30 and change the oil with 5 quarts of the same oil. The 350 won't mind 10w30 at all. It may even like it better.

 

[SLATRON]

I'd just go buy a jug of QSGB, defy or QSUD 5w30 at wally world and mix with that.

 

[dave1251]

Or if you can get PYB, Certified(Sam's Club), or Formula Shell for less mix it with your QSAD and you will be fine.

 

[gregk24]

I would go buy 2 more quarts (or whatever it takes) of Quaker State 10w30 and finish it off with that. I dont like mixing oils, but your engine wont blow up if you do.

 

[fdcg27]

I'd mix it with any two quarts of any SOPUS 10w30 and call it good.
For the temperatures from here through fall, it'll be fine.

 

[901Memphis]

Do you have any oil burners? Any out outdoor power equipment? Just keep the three quarts for top off or OPE and buy some 5w30 synthetic for the PA winters. You will be back in the cold before your oci comes up again it sounds like so be prepared.

 

[datech]

I have mixed Mobil 1 with NAPA synthetic 0W-20 and it worked fine.

 

[901Memphis]

The mixing is fine, I just thought I'd offer alternatives

 

[Dallas69]

Mixing wont hurt at all
I would not recomend going to synthetic in a high mileage car though
I have a 1987 Ford pick up with 155,000 on it and I got a bunch of jugs of PU for 5 bucks each and decided to use some
Well after awhile I had a rear main leak and a pan leak that I never had before
I always thought this was an old wives tale but not now
I am now using Maxlife so I will see for myself if it will help
Anyway,I think it is ok to mix any name brand oil

 

[Merkava_4]

Originally Posted By: salv
The 350 won't mind 10w30 at all. It may even like it better.


They actually do better with 10W-40 in the UOA section I've noticed.

 

[Oil Changer]

Oils fall in and out of favor on BITOG. Way back in the day all the talk was over Amsoil's HDD 5w30. That oil produced some of the best UOA's ever posted.

 

[wolfehunter]

Thanks for the advice. Plan to get two quarts of conventional 5-30 and add to the 3 qts of QS I dumped in last night. Dallas 's post makes me a little nervous though. Is there any truth to the "wives tale" he mentions about switching to synthetic in high mileage vehicles causing oil leaks? Just last week I switched my 2007 Accord 2.4 with 140K from conventional 5-20 to Pennzoil Platinum 5-20 to take advantage of the FRN gas rewards at Shell. Please tell me it is in fact a wives tale!! Was considering going to synthetic in the wife's Toyota Sequoia with 165K but may need to reconsider?

 

[Oil Changer]

Most old wives' tales base their origins in truth. Seals in a neglected engine can become coated in varnish/sludge. That coating of varnish/sludge prevents the oil from lubricating the seals. Switch to a quality (e.g. synthetic, HM) oil and that oil removes the varnish/sludge to expose the seal. If the seal is too far gone, the seal will leak and there is no oil that will stop it. However, if the seal is not too far gone, the freshly exposed seal will soften and/or swell from the additives and the leak will stop. Then there's the possibility you will notice no change. Roll the dice.


Originally Posted By: wolfehunter
Please tell me it is in fact a wives tale!!

 

[datech]

Originally Posted By: wolfehunter
Thanks for the advice. Plan to get two quarts of conventional 5-30 and add to the 3 qts of QS I dumped in last night. Dallas 's post makes me a little nervous though. Is there any truth to the "wives tale" he mentions about switching to synthetic in high mileage vehicles causing oil leaks? Just last week I switched my 2007 Accord 2.4 with 140K from conventional 5-20 to Pennzoil Platinum 5-20 to take advantage of the FRN gas rewards at Shell. Please tell me it is in fact a wives tale!! Was considering going to synthetic in the wife's Toyota Sequoia with 165K but may need to reconsider?



The issue is really about past maintenance. If the vehicle had infrequent oil changes you might see a problem but not just because of using synthetic.

 

[dave1251]

Originally Posted By: Merkava_4
They actually do better with 10W-40 in the UOA section I've noticed.


But 10W40 have a greater chance of producing varnish like when you do your business on the bathroom throne.

 

[Shannow]

Originally Posted By: dave1251
Originally Posted By: Merkava_4
They actually do better with 10W-40 in the UOA section I've noticed.


But 10W40 have a greater chance of producing varnish like when you do your business on the bathroom throne.


There's obviously a physical principal rather than a crude analogy in your statement...please elucidate...

 

[dave1251]

Originally Posted By: Shannow
Originally Posted By: dave1251
Originally Posted By: Merkava_4
They actually do better with 10W-40 in the UOA section I've noticed.


But 10W40 have a greater chance of producing varnish like when you do your business on the bathroom throne.


There's obviously a physical principal rather than a crude analogy in your statement...please elucidate...


Here is my crude response.

Polymers are suitable and commonly used as a viscosity index improver(VII'S) for lubricating and may cause varnish or sludge because of a thermal breakdown due to heat, also oxidation is referred as thermal breakdown, there is also "shearing" of polymers, and fuel dilution can cause a polymer break down out of the oil causing the formation of varnish.

There is a greater risk involved in using a multiple grade PCMO in this instance a 10W40 of the VII's breaking down just due to the amount of VII's used to obtain the spread of a oil that flows like a 10 grade but is a 40 grade oil.

The original response is because the poster quoted prefers to use a more viscus grade of PCMO but also has a obsession of not having varnish in his engine. SO IMO a compromise will have to be made in the future to suit his desires.