It has to be attached to the radiator itself somehow. If the rad cap never opens up to allow (hot, pressurized) coolant to 'expand' into the overflow tank, then you will never see combustion gasses either.

There is no radiator cap. It was hot in the expansion tank, hot coolant was running into the expansion tank during the test. Some pressure was trying to build as even when I was not pumping the tester, bubbles were coming up once it got hot.

Maybe get one of those universal-fit "T" adaptors for the upper radiator hose and a couple of chunks of same-size radiator hose and try that?

You need a special adapter for the reservoir......

What is stupid is, instead of designing the reservoirs the same, there are so many different adapters per platform and per year....

That ain't right! Thinking it could be a carbon build up on cylinder 4 exhaust valve, I filled the cylinder with seafoam a few days in a row and let it soak. Emptied the cylinder of any liquid, upon start it smoked like crazy, then smoke from the FRONT! Cracked exhaust manifold right in front of the O2. I'm going to try some high heat stuff, though, I doubt it'll hold, it should tell me if that'* my misfire. If it is, I'll put of new manifold on and hopefully close out this thread.

I never knew a cracked exhaust manifold can cause a misfire.

Same here, and low compression too.

I'd not throw money or effort into an exhaust manifold for a sick engine.

If anything, it should have set a lean code for the O2 sensor, causing the engine to run rich and could foul the plugs, and even the sensor...

I'm not replacing the exhaust manifold until I've patched the hole and checked diagnostics for a misfire. I'll report my findings soon.