one cylinder running colder than the rest.....

[427.060]

Could it be a bad plug wire or spark plug?
James

[VintageMusclecar]

What intake and carb?

Assuming this was 100° at idle?

How does the plug look on the cool cylinder?

[sYc]

If there are other problems, such as a miss, exhuast smoke, ??? then you may have a problem, but 100 degrees does not sound like much to me. The reason I say this, the amount of fuel or lack of it each cylinder receives affects the temp, which means for all cylinders to be the same temp, the carb/intake would have to be suppling the same amount to all cylinders, which is is ideal, but nearly impossible, especially at idle.

Besides fuel, the other thing that can easily affect temps is valve settings.


We check temps, but are looking for a "cold" pipe, which means a cylinder is not firing. As long as they are all heating up, and no other problems, good to go.

[wagonman]

[ QUOTE ]
If there are other problems, such as a miss, exhuast smoke, ??? then you may have a problem, but 100 degrees does not sound like much to me. The reason I say this, the amount of fuel or lack of it each cylinder receives affects the temp, which means for all cylinders to be the same
temp, the carb/intake would have to be suppling the same amount to all cylinders, which is is ideal, but nearly impossible, especially at idle.Besides fuel, the other thing that can easily affect temps is valve settings.


We check temps, but are looking for a "cold" pipe, which means a cylinder is not firing. As long as they are all heating up, and no other problems, good to go.

[/ QUOTE ]

I agree with this post!
If you were racing it and wanted to run right on the egde of lean,and that 100 degrees brings you over the top.then i would investigate.

If you just cruise and the car runs great with no other apparent problems i think your good to go. 100 degrees doesnt seem alarming....

[JoeG]

Ditto..
Motion would occationally use a colder or hotter plug in different cylinders to try and even things out...when racing...

[sYc]

Yep..forgot about plug heat ranges affecting things. I learned that with single cylinder 4 stroke go-kart racing.

[Dave Rifkin]

Thanks for all of the replies; the car runs fine I just wanted to make sure this wasn't something I should address right away.
For those that asked; it has the stock cast iron intake and Quadrajet carb.
The plugs have just been changed but, I am not so sure about the wires or distributor cap.

[sean70ss]

Usually if a motor is running cooler on a cylinder it is fat I.E. blow by or to much fuel. I would still do a leakdown better safe then sorry but I agree 100 degree temp is not alarming. On a bbc it is hard to tune each specific cylinder eqaully. 8-5 are the most difficult.

Sean

[Verne_Frantz]

[ QUOTE ]
Yep..forgot about plug heat ranges affecting things. I learned that with single cylinder 4 stroke go-kart racing.

[/ QUOTE ]

Tom,
I doubt the plug heat rating will affect the combustion temp. It will affect how long it lasts before melting or fouling. I think that changing a plug heat rating in a cylinder is just a compensation for the heat of that cylinder; not a method of changing the heat in that cylinder.
JMO
Verne

[Chevy454]

[ QUOTE ]

Tom,
I doubt the plug heat rating will affect the combustion temp. It will affect how long it lasts before melting or fouling. I think that changing a plug heat rating in a cylinder is just a compensation for the heat of that cylinder; not a method of changing the heat in that cylinder.
JMO
Verne

[/ QUOTE ]
Verne: a spark plug is doing exactly that, ie, helping regulate chamber (combustion) temperature by dispersing (or not) heat...the amount dissipated has to do with insulator length. I can't remember the exact numbers off the top of my head, but the % of cylinder temp that is transfered via the spark plug is surprisingly (alarmingly!) high...over twice the amount cooled by the charge, I believe?

Stagger jetting and plenum design/alteration can help cover up the distribution problem, but I'm gonna bet Eric has some great info/numbers on this subject...