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

About a month ago I had my car at a new mechanic to see if he could get the car to idle at a normal speed (it had been idling around 1000 rpm; previous mechanic claimed the car had a vacuum leak)
Anyway, he was able to get it to idle around 750 but, told me that one of the cylinders was running about 100 degrees cooler than the rest.
Would this affect the idle characteristics of the car, what could cause this and how badly would it affect the cars performance?

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

Sounds like a broken ring. I would do a leakdown and check all your cylinders.

sean

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

------It could be a ring, but wouldnt that plug be oiled up???.......Bill S

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

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

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

What intake and carb?

Assuming this was 100° at idle?

How does the plug look on the cool cylinder?

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

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.

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

[ 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....

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

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

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

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

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

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.