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Thread: What's the best oil?

  1. #1
    Senior Member
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    What's the best oil?

    standard, synthentic?
    81' gas flap. Sept build. 14k miles. Mostly original. Updating things...

  2. #2
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    Quote Originally Posted by Redsquall View Post
    standard, synthentic?
    Standard. I use Castrol GTX 20W50.
    Early 81 5spd conversion- DMCH Ground Effects, Double Din, Custom Instrument Cluster, QA1 Suspension, 3.0 PRV with MS3

  3. #3
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    Quote Originally Posted by 81dmc View Post
    Standard. I use Castrol GTX 20W50.

    The engine was made to use standard oil, syn is overkill and unnecessary. There are anecdotal cases of old motors used to ordinary oil that when switched to syn, started leaking because the seals get hardened and allow the syn to leak faster. The most important factor is regular oil changes with a good brand of oil.
    David Teitelbaum

  4. #4
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    Quote Originally Posted by David T View Post
    The engine was made to use standard oil, syn is overkill and unnecessary. There are anecdotal cases of old motors used to ordinary oil that when switched to syn, started leaking because the seals get hardened and allow the syn to leak faster. The most important factor is regular oil changes with a good brand of oil.
    The only reason to use synthetic is on a newly-rebuilt motor IMHO.
    Early 81 5spd conversion- DMCH Ground Effects, Double Din, Custom Instrument Cluster, QA1 Suspension, 3.0 PRV with MS3

  5. #5
    Senior Member hmcelraft's Avatar
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    Synthetic is probably best

    I wrote the attached note in 2013 for a previous post. I still use Mobil 1 10W-40 High Mileage Oil and the OEM long block has about 15,000 miles on it now.
    Attached Files

  6. #6
    DMC Midwest - 815.459.6439 DMCMW Dave's Avatar
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    Our normal go-to oil is Castrol 20W-50. If you are the typical low mile driver and change it every year/3000 miles it should be fine. This is the official company recommendation.

    Having torn down a few engines at this point, I'm most impressed with high mile engines that have been running synthetic oil. If you are doing that I typically use Mobil 1 15W50. NOTE this is my opinion based on observation and personal use. Mobil does not recommend synthetic in this engine probably because they have not tested it. Do this at your own risk.

    I also recommend against changing to synthetic oil on an engine with unknown history and/or without a look under the valve covers. I have seen an instance where a somewhat grungy engine was switched to Synthetic, and the grunge inside started to come loose and plug things up. If there are deposits on the inside of the engine stick with the regular oil, and change it more often.
    Dave S
    DMC Midwest - retired but helping
    Greenville SC

  7. #7
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    I use Brad Penn 20W50. It is basically the old green Kendall GT1, made in the former Kendall refinery. It has a high zinc content by modern standards, which may be beneficial for our cams and rocker arms. Castrol GTX 20W50 is also well-regarded.

  8. #8
    Senior Member Bitsyncmaster's Avatar
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    I bought my D with 22,000 miles on it and I run MOBIL 1 since. Last year I did valve gaskets and could not believe how clean the valve covers were. I've rebuilt many other engines in my life and valve covers always have a lot of gunk in them.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  9. #9
    Linux Janitor novadmc's Avatar
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    Quote Originally Posted by 81dmc View Post
    Standard. I use Castrol GTX 20W50.
    same here. I change it once a year (since i only drive about 1500-2000mi/year)

  10. #10
    Guy with a DeLorean Mark D's Avatar
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    Same here, I use Castrol GTX 20W-50.

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