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2001 DHS
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Discussion Starter #1
I have 5W30 conventional oil in my car now. It's low about 2 qts. Is it Ok to top it off with 0W40 Synthetic ? I have a few bottles laying around and wanted to know if I can use them in my Caddy.
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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26,323 Posts
Mixing conventional and synthetic is just fine.

0W-40 is thinner than spec cold, and thicker than spec when at operating temp.

Adding only 2 quarts to the 5.5 quarts of correct viscosity oil already in there isn't that big of a deal. If it's all you have right now, go ahead. But next time use the correct viscosity, don't keep adding the wrong one.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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69,894 Posts
Have at it, but don't make it a habit - especially if the oil is from 2 different brands/refiners - the additive packages may not be compatible.

Let's see -

5.5 quarts at 5W is 27.5, add 2 quarts of 0W, then 27.5/7.5 = 3.7W

5.5 quarts at 30 is 165, add 2 quarts of 40, then 245/7.5 = 32.7

3.7W - 32.7 oil is perfectly fine.

Before someone broaches the subject of mixing conventionals and synthetics, just what is the ratio of a "Synthetic blend" ? ......... and consider that the name "Conventional blend" would not sell as much oil........ :lildevil:
 

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White Diamond '03 DHS (with DTS floor shift)
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87,196 Posts
If you are trying to get rid of the 0W40, just add one qt at each oil change. It'll have less of an effect at that point.
 

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1996 Deville Concours
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805 Posts
Won't hurt anything, but might want to consider your climate. The "operating temp" weight is achieved by adding that chemical (ZDP I think?) that expands...so something like 0W-40 is basically a very thin oil with a lot of that additive (maybe even a synthetic exclusive, I'm not sure though). The only reason you'd need 0W-anything is if you're in a regretable location such as Minnesota this time of year. Having the oil thinner at startup temps is good so it's oil and not tar hehe. That's actually pretty much the only way synthetic oil has a worthwhile advantage over normal oil--that extreme cold capability. Remember too, that after sufficient driving, the additive that makes that upper weight (40) breaks down (one of the few reasons we still have to change oil at some point no matter how good refining has gotten), so you don't really have 5w30 after a couple months...might be 5w24 or something :p.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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The ZDDP additive package has exactly NOTHING to do with oil getting thicker or thinner. ZDDP is an anti-scuff zinc/phosphorus compound added in differing amounts for specific oil use categories. The perceived viscosity change is due to refining techniques and other additive packages.

Mercedes and Ferrari run 0W-40 oils year-round. Yes, the stuff is great for lessening cold starting drag in engine parts - but, as posted, you can mix it in small ratios with any other multigrade oil and safely "use up" some spare oil. Always best to stick with the manufacturer's viscosity recommendations for any particular engine.

If someone is really anal about oil performance over time, use the test facility offered by Blackstone Labs. That is the truth - not hearsay.

http://www.blackstone-labs.com/free-test-kits.php
 

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2001 DHS
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Discussion Starter #7
I live in an area where temperatures are -30 in winter and 95 in summer. So basically I should stick to the recommended 5W30 year round? Even in extreme winter?
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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.............. and look at the temperature "thermometer" that gives oil viscosity recommendations - in the owner's manual.
 

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0W-30 Synthetic would be even better than 5W-30. That's all I ever used since 1996.

0W-30 is rated to -35 F

Here is a page from my owners manual.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Heck - go up and fool around in the Escalade forums - the new ones take 8.5 quarts of 0W-20 - year 'round. My F-150 4.6 runs 5W-20 - year 'round.
 
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