Exhaust manifold heat riser valve question

[Sonny]

I’ve been having an issue lately with my ‘78 360. When I go over 60 miles an hour, I’m getting a roaring sound from the exhaust like surging. However the engine is not surging. It’s very rhythmic and only happens at steady cruise. Accelerate or decelerate and it quits. It’s clearly exhaust. l noticed my passenger exhaust manifold has a riser valve. l spun it by hand and the spring fell off. Now it spins VERY easily. Could it be opening and closing during cruise mode? l have 2.25” exhaust with an H pipe. Am l crazy?

 

[69L48Z27]

Try to wire it open. I'm trying to remember how that was configured on my LRE we had. Most of them you can keep open.

The sound your describing makes me think fan clutch. Not sure if the car your working has one or not.

 

[Sonny]

Try to wire it open. I'm trying to remember how that was configured on my LRE we had. Most of them you can keep open.

The sound your describing makes me think fan clutch. Not sure if the car your working has one or not.

come to think of it, l added a clutch fan 2 months ago. Didn’t have one before. Hmmm.

 

[Sonny]

l bought a cheap one from Napa. Can anyone recommend a good one?

 

[69L48Z27]

Make sure that's really the problem before you replace. Can you put the old fan back on? I could be all wrong. What you described just reminded me of an osolation that a fan clutch might produce. If you got it at Napa try to exchange it for a new one if you also think that's what it is.