Exhaust Manifold Leak ? Or Maybe Not...

OK, so I was 99.9999% sure I had an exhaust manifold leak. I have all the ticking that indicates there's a manifold leak etc... (loud metallic ticking, more pronounced in the cold) and under slight load at lower RPMs.

Anyway...I ended up smoking it (using a smoke machine to test for leaks through the exhaust) and I couldn't find any exhaust leaks. Maybe the machine wasn't strong enough to get the smoke from the tail pipe to the manifold or maybe there's no leak?

I'm going to get it on a lift next week and use some soapy water.

 

visual inspection
Soapy water when cold

Another option is combusting smoke such as seafoam that smokes white out the tailpipe. If there’s a manifold leak the seafoam smoke show might be evident there too in theory.

 

Look for black soot around the manifold and exhaust connections

 

Well, I was going to Seafoam my truck anyway - but I'll also try soapy water. Thanks.