Using Synthetic Oil in Classics

Discussion in 'Classic Mustang Specific Tech' started by 65and68Stang, Aug 6, 2003.


  1. 65and68Stang

    65and68Stang New Member

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    I did a search of the Classic Forum for synthetic but didn't come up with anything, so...

    Would there be any benefit to using synthetic in my '68 302. It is a brand-new rebuild (0 miles) with forged internals, new rings, pistons, etc.

    I've always heard that you shouldn't use synthetic in old (worn out) engines, but does that apply to old (like new) engines as well?

    Thanks! :banana:
  2. Ozsum67

    Ozsum67 Too much thin air Founding Member

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    Sure, you can use it and get all the benifits........just use it after it is broke in. New car manufacurers use a synthetic blend, so the rings will seat. Then, just switch over after 500 miles. I use Mobile1 5w30 in my stock 289. I would suggest getting a magnetic oil drain plug too. Every little bit helps keep the abrasives out of the oil.
  3. Realmongo

    Realmongo I prefer to be called "Evil Genius" Founding Member

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    I know that Crane Cams did not reccomend the use of synthetics until at least the engine is broken in, but then after that it should work out great!
  4. 70stangcoupe

    70stangcoupe Founding Member

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    So a motor with ~3k miles is okay for Synthetics?

    Isn't it bad for leaking?
  5. Ozsum67

    Ozsum67 Too much thin air Founding Member

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    Only if you have a leak. It is still the same weight, it may have better detergents to clean away gunk, which might make a leak start, but with 3000 miles, the engine should be clean already.
  6. 65and68Stang

    65and68Stang New Member

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    Okay, so start with a standard oil through break in (500 miles) , then at the first change I can switch over to synthetic, correct?

    Thanks guys!
  7. Ozsum67

    Ozsum67 Too much thin air Founding Member

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    :nice: :nice: You may, I repeat MAY see some consumption issues. Depends on your tolerances. Obviously close tolerance won't be any issue, but my 97 F150 has always like a little synthetic between oil changes, where it doesn't use a drop of regular oil.
  8. Great68

    Great68 Founding Member

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    I use Mobil 1 15W50 in my 289, I must say that it did make my car start to leak a bit of oil (It never did with conventional oil).

    I also use synthetic gear oil in my differential.
  9. electricgreen

    electricgreen Founding Member

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    We plan on running Royal Purple in the Mach next year, after we drive it a bit this year for a break in period. It was rebuilt before we bought it, but we don't know how many miles ago (somewhere in the range of 500-900 miles).....We run Royal Purple in the 00 too.
  10. Ozsum67

    Ozsum67 Too much thin air Founding Member

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    I'm thinking maybe the 50w had something to do with it. More oil pressure. You may actually be starving the engine of oil too. What kind of pressure are you getting?
  11. The Dan

    The Dan New Member

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    I think the whole synthetic oil being too slick for break in is more of a myth. I say this because my 02 Harley F 150 came from the factory with 5w-20. I ran it for the first 500 with that oil and have been running Mobile 5W-30 ever since with no problems or comsumption. In addition I have a 03 Harley Road King Classic and Harley states right on their Synthetic Oil that it's ok to run their synthetic for engine break in. So there's two different manufactures saying it's cool to run it right out of the gate. Just an FYI, do what ever you feel comfortable with.

    My 65 Fastback will be running Mobile 5W-30 and I don't anticipate any problems, just a cooler running engine.
  12. Ozsum67

    Ozsum67 Too much thin air Founding Member

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    I agree, in that some vehicles, synthetic is good right out of the factory. New Vettes come with Mobil1. It is all in the design and what has been engineered in them. In the case of his 289, things need to wear in before he can use synthetic oil, unless he wants to keep adding oil.
  13. mustangdave

    mustangdave My rearend needs a stud and two nuts. Founding Member

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    The top of the line,(if you want to call it that), Auto Zone engines also come with synthetic oil in them. I don't think the tolerances are that good in these engines and they do o.k. If you are worried, run the regular stuff until the first change.
  14. SoCalCruising

    SoCalCruising Founding Member

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    Ya know, this has to have something to do with the way the bores are honed. The hot ticket these days is to get a "plateau" pattern that has fairly deep grooves but a flat surface between grooves. Kinda like:
    /\_/\_/\_/ . The grooves trap and hold oil for lubrication and the flats provide excellent ring seal. It may be that this technique reduces break-in and the motors are essentially broken in almost immediately. Rings would be spec'd accordingly. This would allow the use of a slicker synthetic right from the factory.
  15. Ozsum67

    Ozsum67 Too much thin air Founding Member

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    I was trying to get there. Thanks for the clarafication. :lol:
  16. Great68

    Great68 Founding Member

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    Hmmm. I never thought of that. According to my oil pressure guage, the needle is right where it should be though. Maybe I should change to 10w30?
  17. Ozsum67

    Ozsum67 Too much thin air Founding Member

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    Yea, something to think about. The thicker the oil, the more pressure, but less oil circulating and vise versa.
  18. cobrajet

    cobrajet Founding Member

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    I use Mobil 1 5w30 in my 428CJ race car. I had the engine apart last year and looked just as clean as when it was put together. There was no wear in the cyl and the bearings looke like new.
  19. tacoy

    tacoy Founding Member

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    I didnt quite see an answer to my problem so I'll ask. I currently run 20-50w. I bought some mobil1 15-50w. I was hoping to try it. My engine has only 45k miles on it but it's 25 years old. first one siezed at 100k. It doesnt leak and I'm worried that I'll make it leak. If it does and I go back to convential will it stop or have the seals been damaged so that it will not stop leaking? the old owner ran 10-30w in it. My mechanic told me he wants the most engine compression and he runs 20-50w in all cars over 75k
    Thanks for your replies here are some of my engine specs
    289
    2bbl with 500 cfm holley
    bored 30 over
    Thanks In Advance
  20. Edbert

    Edbert Founding Member

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    Guys, help me out here. HOW can a synthetic oil of a given weight leak through holes that a conventional oil of the same weight cannot? I can (maybe) see that 5W could possibly leak from an engine that had no leak with 30W but come on. Either your engine has a leak or it doesn't, "slickness" of the oil does not CREATE leaks.

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