Different cylinder temps question

Engine, Transmission & Driveline

  1. 67Monaco

    67Monaco Old Man with a Hat

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    Setting up the Derale electric fan control yesterday and while I had the infrared gauge out I took some measurements of the header temp at each cylinder.

    Engine was warm up to 190, cylinders 1,2,7,8 were pretty close to each other in the mid 600's (F). 3,4 were a bit lower but nut much, high 500's to low 600's.

    5 and 6 is where my readings went all cattywompus. 5 hit about 748 on the upper end and 6 was in the upper 400's. Sparkplug #6 looks good, seems to be firing so I don't think there's a miss there.

    So I'm trying to think this through and figure out my discrepancy. Only thing I can come up with is maybe a vacuum leak in the intake gasket @#5 causing a lean condition thus burning hotter. Anything else anyone can think of?
     
  2. 65Fury440

    65Fury440 Senior Member

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    So my headers are about 100 degrees cooler on #1 and #2, which are also the longest straight runs after the bends.

    I made it a point to check at the center of the port exit on the outside of the initial bend for uniform temp. It seemed to matter when taking temps.

    On my deal, single plane intake, those are longer intake ports, and longer primary tubes, not sure if it amounts to a hill of beans, watching this thread though for more info.
     
  3. 67Monaco

    67Monaco Old Man with a Hat

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    I'm taking my readings as close to the flange as possible.
     
  4. saylor

    saylor Senior Member

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    just as a curiosity, when you scan around the block, what does that look like?
    i got a HFT temp gun and hit the top of the intake/valley pan somewhere and it said like 290* IIRC and i was like holy crap.
    i have no idea what a person should hope to see.
    i did read we should see a ~30* temp difference between top rad and lower rad hose - proves rad is doing stuff..

    try not to die -

    - saylor
     
  5. 67Monaco

    67Monaco Old Man with a Hat

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    Next time I'm out with it i will. I know it's hotter elsewhere, but I was concentrating on the core plug next to the heater nipples. Then just scanned the headers a couple times.
     
    Last edited: Dec 13, 2019
  6. CBODY67

    CBODY67 Senior Member

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    Might need to put a "scope" on the engine to look at spark plug firing voltages, to verify how "well" the plugs are firing.

    For general information, you might also check the cyl block sides, front to back, as the rear of the motor usually sits lower than the front, that's where the sediment will settle out, which can cause some cooling issues with time. Issues which can be cured with a R & R of the core plugs and a cooling system flush (with the plugs removed).

    Also, after driving the car on the highway for about 10 miles, seeing where the oil filter temp might be. The engine coolant temp will come up first, but it takes more "loaded" run time for the engine oil temp to approach the coolant thermostat opening temp.

    Just some thoughts,
    CBODY67
     
  7. mr. fix it

    mr. fix it Old Man with a Hat

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    Is this a new build or a seasoned engine?

    My engine experience as a tradesman indicates the following possibilities

    1) exhaust valves are new & not properly seated which allows fuel to continue burning in the exhaust tube on the high temp cylinder
    2) Burnt or next to burnt valve
    3) tight valve again allowing un-burnt gases into the exhaust tube

    How's the compression for the cylinders?
    Is it hydraulic or solid lifter cam?
    It could be an improper air/fuel mixture as well
    It could be ignition is not 100% in good tune.

    All things to check out.

    Above items listed in replies by others are good things to check as well because of the age of the block itself.
     
  8. 70bigblockdodge

    70bigblockdodge Old Man with a Hat FCBO Gold Member

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    That does not seem out of wack oil temp of 100° over water temp and without a engine oil cooler is I would say ballpark on a up to temp engine. Water temperature is always the lowest in the engine as it is removing the heat from higher temp pieces.
    I would say ignition on 6 , and something is not sealing on 5. Compression check and vacuum readings next.
    Is it a single plane or dual plane. If single it may just be the firing order. The end cylinders fire front to back then the center 4 fire in order 3,4 while nothing happening at rear half of the manifold 6 ends up rich and cold then 5 gets starved, and hot.
     
    Last edited: Dec 14, 2019
  9. 67Monaco

    67Monaco Old Man with a Hat

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    Vacuum is strong and compression on all the cylinders is within about 10% of each other.

    This is the engine I replaced the timing chain on a few months back that was about two teeth off when it slipped. I would think nicked a valve when that happened but the readings are good.
     
  10. 67Monaco

    67Monaco Old Man with a Hat

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    Factory engine that came with the car. Other than replacing the timing chain, and the headers it's as it came from Ma-Mopar. Well that and the 69 AVS my wifes grandfather put on it when he acquired it.

    Granted it has 130K miles on it. Don't smoke and still runs like a raped ape otherwise.
     
  11. 70bigblockdodge

    70bigblockdodge Old Man with a Hat FCBO Gold Member

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    With stock dual plane I would not sweat it that much could be just the way the fuel is puddling in the intake
     
  12. mr. fix it

    mr. fix it Old Man with a Hat

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    are the cylinders with the higher temps lower in compression than the others?
    Also, I am presuming hydraulic lifters if it's all factory.
     
  13. 67Monaco

    67Monaco Old Man with a Hat

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    You know I didn't think about that, these are all idle exhaust temps. Maybe it evens out off idle?
     
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  14. 70bigblockdodge

    70bigblockdodge Old Man with a Hat FCBO Gold Member

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    If it is idling smooth and no hiccups I would not sweat it.
     
  15. 67Monaco

    67Monaco Old Man with a Hat

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    Lopey, but that's normal for this engine from the history I have with it.
     
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