Heat riser spring and weight
 

Does anyone know offhand which direction these work?

Does the weight pull it open or hold it closed?

Does the spring pull it open or hold it closed?

I assume they work opposite each other and the spring is thermal, but I don't know which does which job.

I'm trying, in the end, to figure out what happens when your heat riser gets old and maybe the spring gets weak. Does it fail to close or fail to open properly?

Re: Heat riser spring and weight
 

The weight (and exhaust flow) opens it.

The spring holds it closed, when exhaust isn't forcing it open.

I would say if the spring is weak, it won't close as fully as it should.

Re: Heat riser spring and weight
 

The weight pulls it open. The spring is a bi-metal spring that holds it closed until it heats up.
If yours is sticking so it doesn't open or close, you can buy a special lubricant and try that before buying a new heat riser.

Re: Heat riser spring and weight
 

Thanks guys! Mine doesn't stick, it just stays somewhat closed and bounces around at hot idle, when I think it should be fully open. Not stuck though.

Re: Heat riser spring and weight
 

This is the current GM version of the lubricant. Probably graphite based.

https://www.amazon.com/Genuine-Fluid.../dp/B00BK7MLKE

Re: Heat riser spring and weight
 

Sounds normal. Will open fully due to exhaust flow at higher RPMs as Stocker said. They also may rattle at times.