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Thread: Spark plugs

  1. #1
    Mad scientist DrWin's Avatar
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    Spark plugs

    So - I changed the sparkplugs today and got these out:
    DSC_0510.jpg
    Can we tell anything about the state of the engine from looking at the old sparkplugs?
    I put in the NKG ones, as they were the ones I had handy. Is there anything better available?

    As allways, thanks for any input!
    Please excuse the crudity of this DeLorean as I didn't have time to repair it yet.
    VIN 10207 - December '81, Gray Interior, 3-speed automatic, stock PRV engine.

  2. #2
    Senior Member
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    Quote Originally Posted by DrWin View Post
    So - I changed the sparkplugs today and got these out:
    DSC_0510.jpg
    Can we tell anything about the state of the engine from looking at the old sparkplugs?
    I put in the NKG ones, as they were the ones I had handy. Is there anything better available?

    As allways, thanks for any input!
    Need to look at the ignitor end not the threads. A normal color would be a tannish color. Black color that coats everything and looks dry or ashy means it's running too rich; check your CO and check that your O2 sensor wasn't fouled up as well (it would have the same coating). Black color that has a shine to it means you have oil fouling from worn rings or leaking valves; check the compression of the cylinder(s).

  3. #3
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    "Reading" spark plugs is close to reading tea leaves. While it can give you some information, you need other, confirming information too. Black plugs can be because of a bad crankcase ventilation system, an overfilled crankcase, or even a car that is only used on very short hops and never warms up for example. Or maybe the wrong heat range. Used in conjunction with a compression test and a leak-down test and an accurate measure of the oil pressure, you can get a good idea of the general health of the motor.
    David Teitelbaum

  4. #4
    Senior Member DMC-81's Avatar
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    You can tell a lot about the condition of the engine by looking at the spark plugs. Just Google "spark plug condition chart" and pick your favorite chart.

    The spark plugs in your picture look to be the OEM spec, i.e. Bosch Silver HR6DS. They are discontinued so IMO, I would hang onto them if originality is important to you.
    Dana

    1981 DeLorean DMC-12 (5 Speed, Gas Flap, Black Interior, Windshield Antenna, Dark Gray)
    Restored as "mostly correct, but with flaws corrected". Pictures and comments of my restoration are in the albums section on my profile.
    1985 Chevrolet Corvette, Z51, 4+3 manual
    2006 Dodge Magnum R/T (D/D)
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  5. #5
    Mad scientist DrWin's Avatar
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    Quote Originally Posted by dmcman73 View Post
    Need to look at the ignitor end not the threads. A normal color would be a tannish color. Black color that coats everything and looks dry or ashy means it's running too rich; check your CO and check that your O2 sensor wasn't fouled up as well (it would have the same coating). Black color that has a shine to it means you have oil fouling from worn rings or leaking valves; check the compression of the cylinder(s).
    Black and dry, so rich, I'm assuming. That lines up with everything else I've seen from the car so far.

    Quote Originally Posted by David T View Post
    "Reading" spark plugs is close to reading tea leaves. While it can give you some information, you need other, confirming information too. Black plugs can be because of a bad crankcase ventilation system, an overfilled crankcase, or even a car that is only used on very short hops and never warms up for example. Or maybe the wrong heat range. Used in conjunction with a compression test and a leak-down test and an accurate measure of the oil pressure, you can get a good idea of the general health of the motor.
    Roger - We're waaaaaay out of my competence zone here - I have zero idea what that means. But thanks, this might be the kind of post I can get back to and actually use later, when I've done som more wrenching and research.

    Quote Originally Posted by DMC-81 View Post
    You can tell a lot about the condition of the engine by looking at the spark plugs. Just Google "spark plug condition chart" and pick your favorite chart.

    The spark plugs in your picture look to be the OEM spec, i.e. Bosch Silver HR6DS. They are discontinued so IMO, I would hang onto them if originality is important to you.
    Thanks - they are. Originality isn't important to me - I'm more in the improve-it-if-it-can-be-done-w/o-affecting-the-visual-appearence camp. I'll pick them out of the trash and save them for someone else who might enjoy them.
    Please excuse the crudity of this DeLorean as I didn't have time to repair it yet.
    VIN 10207 - December '81, Gray Interior, 3-speed automatic, stock PRV engine.

  6. #6
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    Iím not sure how you guys overlooked the pictures I posted to the thread below.
    There are pictures of eighteen different spark plugs and a description of each and every one.
    I posted the pictures 2,473 days ago. Yes, I counted the days since April 19, 2015.
    DrWin what can I tell from your picture? It would help if the picture was taken outdoors in the sunlight to better see the central electrode.
    http://dmctalk.org/showthread.php?11...ng-spark-plugs
    Mark Vanyo
    Links to DeLorean related web sites!
    http://dmctalk.org/showthread.php?19...s-Part-I-of-II.

  7. #7
    Mad scientist DrWin's Avatar
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    Thx

    Quote Originally Posted by outatym2001 View Post
    Iím not sure how you guys overlooked the pictures I posted to the thread below.
    There are pictures of eighteen different spark plugs and a description of each and every one.
    I posted the pictures 2,473 days ago. Yes, I counted the days since April 19, 2015.
    DrWin what can I tell from your picture? It would help if the picture was taken outdoors in the sunlight to better see the central electrode.
    http://dmctalk.org/showthread.php?11...ng-spark-plugs
    Thank you! I have picture 4 - carbon deposits.
    Please excuse the crudity of this DeLorean as I didn't have time to repair it yet.
    VIN 10207 - December '81, Gray Interior, 3-speed automatic, stock PRV engine.

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