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  1. #1
    Jr. Engineer JTWard's Avatar
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    Question The old and new of oil ?

    I have a now, after long last a restored 1990 Chevy Silverado. And I wanted some of your opinions. What are the pro's & Con's of switching my 305 ci V8 from conventional 10W/30 to Synthetic 5W/30 oil ? I was going to try 2 quarts of synthetic with 3 quarts of conventional motor oil. Is there any real benefits or since I only log about 8 or 9 thousand miles a year ? Right now, the seals are dry and tight. Thank you !
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  2. #2

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    Quote Originally Posted by JTWard View Post
    I have a now, after long last a restored 1990 Chevy Silverado. And I wanted some of your opinions. What are the pro's & Con's of switching my 305 ci V8 from conventional 10W/30 to Synthetic 5W/30 oil ? I was going to try 2 quarts of synthetic with 3 quarts of conventional motor oil. Is there any real benefits or since I only log about 8 or 9 thousand miles a year ? Right now, the seals are dry and tight. Thank you !
    Its either one or the other... never mix them. If it were me I'd go with synthetic... in the long run they cost about the same into that synthetic cost 2 - 3 time upfront... but you can go much longer between changes... therefore costs are really a wash. If it were me I go full synthetic.
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  3. #3

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    From everything I've read if you've used conventional oil and the engine has a small leak, using synthetic can cause the leak to get a little worse as synthetic oil usually has a better additive package and will clean sludge. Sometimes the sludge can act as a barrier to keep oil leaks down.

    Now if you've restored the truck and that includes some engine re-building, I say use 5W-30 Mobil 1.


    Quote Originally Posted by TimTom64b View Post
    Its either one or the other... never mix them. If it were me I'd go with synthetic... in the long run they cost about the same into that synthetic cost 2 - 3 time upfront... but you can go much longer between changes... therefore costs are really a wash. If it were me I go full synthetic.
    That is a myth about synthetic. Synthetic oil and convention oil will mix with no ill effects.

    Remember, there are synthetic blend oils out there for sale which is basically a 50/50 mix of conventional and synthetic.

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  4. #4

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    When I switched to synthetic in my truck going from 3k to 6k interval made the cost the same. Your yearly mileage is also similar to mine in my truck so I also only change it once a year if I dont hit the 6k first. Also if you were running 10-30 with conventional why not stick to it with the synthetic (10w-30).

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    Quote Originally Posted by TimTom64b View Post
    Its either one or the other... never mix them. If it were me I'd go with synthetic... in the long run they cost about the same into that synthetic cost 2 - 3 time upfront... but you can go much longer between changes... therefore costs are really a wash. If it were me I go full synthetic.
    My question to the never mix is why do they sell synthetic blends (dino and synthetic mix). Not an oil guru so an honest question.
    David
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  5. #5

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    Quote Originally Posted by dsfloyd View Post
    Not an oil guru
    None of us are, haha. Just a bunch of guys with STRONG opinions.

    Here's mine.

    They do sell a blended oil product. Why, I don't know, I see no advantage, probably to keep the cost per quart down. I consider it a half-ass product, with half-assed results.

    I use synthetic because I like to use it. There is a cold weather start advantage for me (Canadian winters) and I like to extend the change interval; but, conventional oil will work just as well in our street trucks.

    But, I would go with one, or the other, or purchase the factory blended version. I see no advantage in using a "personal" blend.
    Ray

    '09 Avalanche LTZ - Black
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  6. #6
    Jr. Engineer JTWard's Avatar
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    That's a good point. I'm wondering that since the engine has always had a steady diet of 10W/30 conventional oil, why risk a leak of and ill effects. It has been run on 10W/30 dino, I just stay with what has worked Ok in the last 22 years !

  7. #7

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    Quote Originally Posted by RayVoy View Post
    None of us are, haha. Just a bunch of guys with STRONG opinions.

    Here's mine.

    They do sell a blended oil product. Why, I don't know, I see no advantage, probably to keep the cost per quart down. I consider it a half-ass product, with half-assed results.

    I use synthetic because I like to use it. There is a cold weather start advantage for me (Canadian winters) and I like to extend the change interval; but, conventional oil will work just as well in our street trucks.

    But, I would go with one, or the other, or purchase the factory blended version. I see no advantage in using a "personal" blend.
    Starting in 2011, GM is requiring dexos approved oils and it appears that all oils to be on the dexos1 approved list are either a synthetic blend or fully synthetic.

  8. #8

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    Quote Originally Posted by stchman View Post
    Starting in 2011, GM is requiring dexos approved oils and it appears that all oils to be on the dexos1 approved list are either a synthetic blend or fully synthetic.
    I know that, but we're talking about a 1990 Silverado.

  9. #9

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    Quote Originally Posted by stchman View Post
    From everything I've read if you've used conventional oil and the engine has a small leak, using synthetic can cause the leak to get a little worse as synthetic oil usually has a better additive package and will clean sludge. Sometimes the sludge can act as a barrier to keep oil leaks down.

    Now if you've restored the truck and that includes some engine re-building, I say use 5W-30 Mobil 1.




    That is a myth about synthetic. Synthetic oil and convention oil will mix with no ill effects.

    Remember, there are synthetic blend oils out there for sale which is basically a 50/50 mix of conventional and synthetic.
    My problem with mixing them is that each oil manufacturer tends to have its own proprietary mixture of additives... I guess if you stay with the same manufacturer you'd pretty certain not have any problems... I just do not like the idea of playing chemist and risking a problem. Oil is allot cheaper than a replacement engine.

    Just a little note from a past experience... I once had a local oil change company use the off brand of castrol in my sons truck... it burns a little oil so he mixed oils with another brand. Well after a couple weeks after topping off he noticed his oil pressure going up and down periodically... we just thought the issue was with the gauge or sensor. Then one day when he started it in the driveway he had no pressure and it blew out the seal around the oil filter. Appeared the oil filter was plugged. We immediately changed the oil, filter, did a flush and changed the oil and filter again. All has been fine ever since. Keep in mind that this was over a three month period after a fresh oil change. My point is...is it really worth the risk to save a couple bucks.

  10. #10

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    Check out this brief description. It's still really doesn't answer will synthetic affect an older engine. http://en.wikipedia.org/wiki/Synthetic_oil. Is the engine rebuilt? If you're in the extreme weather range, cold or hot, then switch to synthetic, if not regular oil is fine.

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