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HT4100 4.1, 4.5, 4.9 Discussion, spark plugs in Cadillac Engine Technical Discussion; Hi Guys, What is the spark plug gap in mm for an 83 4100? Also I'm about to change the ...
  1. #1
    Ruud is offline Cadillac Owners Fanatic
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    spark plugs

    Hi Guys,

    What is the spark plug gap in mm for an 83 4100?
    Also I'm about to change the oil...is it still 'safe' to use 15w40 diesel oil?

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    the recluse is offline Cadillac Owners Connoisseur
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    Re: spark plugs

    15w40! WOW! I thought the spec was 5w30? I wouldn't use that heavy an oil in the wintertime...

  4. #3
    steelybill is offline Cadillac Owners Enthusiast
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    Re: spark plugs

    I looked through my manuals, and couldn't find the plug gap, but it's usually in the owners manual.
    I've been using Valvoline racing oil in my 4.1 (VR-1) I don't want to replace the cam again, so with the ZDDP in the racing oil, it may last a while.

  5. #4
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    Re: spark plugs

    HEI can run up to .060"

  6. #5
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: spark plugs

    Quote Originally Posted by Sevillian273 View Post
    HEI can run up to .060"
    Theoretically. I try to tighten it up a little if I don't have to bend the side electrode too much. Hi PO Chevys always ran .045"; somebody figured out that they couldn't handle .060"

  7. #6
    Ruud is offline Cadillac Owners Fanatic
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    Re: spark plugs

    Quote Originally Posted by Sevillian273 View Post
    HEI can run up to .060"
    is that .60 mm?

  8. #7
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: spark plugs

    .060 inch. Sixty thousandths.

    For oils which have an added anti-scuff package (ZDDP) in your correct viscosity range do some research on Chevron DELO, Pennzoil LongLife, and Shell Rotella fleet and marine oils. They are available in 10W-30 and 10W-40 weights and they have about the same anti-wear package as the pre-"starburst" oils.

    15W-40 is really too heavy for a small engine.

  9. #8
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: spark plugs

    IMO, I would only use 15w in a 150K mi+ motor with the oil light coming on at idle(low pressure). Not a fix by any means but cheaper than a rebuild. That situation probably doesnt apply here so I'd go with the recommended weight.

    $0.02

  10. #9
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: spark plugs

    Quote Originally Posted by cadillac_al View Post
    Theoretically. I try to tighten it up a little if I don't have to bend the side electrode too much. Hi PO Chevys always ran .045"; somebody figured out that they couldn't handle .060"
    Makes sense. I run mine at .060 with a MSD 6A box with no problems. The tiniest turn of the crank and she roars to life

  11. #10
    steelybill is offline Cadillac Owners Enthusiast
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    Re: spark plugs

    .060 thousands is close to 1.55 MM For .045 thousands you could use 1.15 MM.

    The .060 inch plug gap presents more potential for the plug wire insulation to deal with, which may be a problem for old wires.

  12. #11
    1copenhagen is offline Cadillac Owners Member
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    Re: spark plugs

    Quote Originally Posted by steelybill View Post
    .060 thousands is close to 1.55 MM For .045 thousands you could use 1.15 MM.

    The .060 inch plug gap presents more potential for the plug wire insulation to deal with, which may be a problem for old wires.
    .060 is what my 85 Eldo calls for and steelybill I think you are right after I changed my plugs I have a miss under heavy acceleration but my car still has the the 1985 wires and cap and rotor

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