Thread: heat spike

Glowing red exhaust manifold usually means either plugged cat (as said), running too-retarded timing or poor valve seating (allows unburnt fuel to combust in exhaust manifold), or running too lean (just gets too hot).

As was said, since it's only one pipe, it's likely not a cat (or for that matter, timing) issue. I guess it could be a bad injector on that cylinder causing leanness, but then you said the problem went away?

(Injectors can have intermittent issues, of course)

And since it did "go away", it's probably not a valve issue.

I'm with those who think it was an air pocket/bubble in the coolant jacket in the head, and it's probably OK (burped itself) now.

But do burp it, keep an eye on it, and keep an eye on that cylinder's injector. If you see redness on that cyl again, switch injectors around and see if the problem follows.