KJL

I am installing some headers and removed a few spark plugs and found that 1/2 the plug (tang and electrode) is a red to redish tan and the other half is a brown to black color. Is this normal? The red color does not seem to fit plug chart cause/symptoms. The engine is a 72 L48. I believe the plugs are the correct heat range. Any thoughts?

HighHopes85

This is a little more detailed than the back of the Haynes manual...

http://www.diy-efi.org/gmecm/papers/plug_cuts.html

Hope it helps, -Matt-

zwede

The red is a fuel additive, most likely to increase octane. Oil companies use different additives, and you may very well find that switching to a different brand of gas will eliminate the red color. It's not a bad thing, though.

Although some people still swear by plug readings, I find it is much less accurate with unleaded gas. Unless something is really off mixture-wise, you're just going to get the color of whatever additive package the oil company is using.

Larry B.

I have seen the reddish look before and that used to be a "Shell "gas thing. I suspect it is some sort of additive in whatever type of gas you are using. You might try a couple of tanks of another good fuel such as Amoco premium (93 octane) :chevy

HighHopes85

Wow, the last 2 posts helped me out...I never thought about that. With winter coming, I assume this would change the additives and possibly give even more different colors? -M-