TJ, me either, and there are more than those. I agree the best test is a combustible gas test, but it sounds like the advice given will still fall on deaf ears.

Things don't happen for no reason. At least that's been my experience.

OMG, and I thought I was the only one LOL, I even had my brother in Ca. check to see if maybe my font's were white and not visible. LOLA.

Well, its not really falling on deaf ears. I'm going to change the fluid in the spring and then see what happens.

Also, to clarify, this gets to look like coffee. You can still see through it when its, say, a stream less than 3/4" deep.

But you should explain to all here how combustion gas at 500psi plus doesn't pressurize a 7 pound cap on the radiator. I'm willing to learn here, just don't see how that happens.

I will be the first to admit, your problem doesn't seem straightforward. From your initial post, "Anti-freeze put in, cam broke in. Took car around the block and parked it. 6 months later (or maybe immediately) the stuff is the color of strong strong coffee." From this if you break in a cam like I do (20 minutes), breaking in the cam, a trip around the block, and some miscellaneous time, you have probably, what, about 30 minutes total on the engine? That doesn't sound like a lot of run time to develop your problem. But you have to start somewhere and an antifreeze check eliminates both combustion gasses and oil contamination and could prevent you from wasting a coolant repalcement. Can a head gasket leak and not lift the radiator cap? No. But a slight leak just gets vented.

Am I reading this correctly? Are you putting it out there you did a compression test and you've got 500 psi?

No. Every time a cylinder fires, the combustion pressure is (actually quite a bit higher than) 500 psi.

I should point out that I had a turbo car once that blew a head gasket from detonation - it would run completely normally for hundreds of miles UNLESS I hit the boost. No brown coolant, no overpressure in the radiator. But even at 3-4 psi boost, the car would overheat within 30 seconds and puke all the coolant. Wait for it to cool down, refill radiator, drive again for hours. I finally pulled the head and the fire ring on one cylinder was pushed out to where it just reached a cooling passage.

So head gaskets can do strange things.

Thank you for posting that. I worked on a srt4 that did the same thing. Customer could not understand that when you put 30 lbs of boost to a build, everything better be up to snuff. The mopar oem head gaskets almost did the job.

An alternative method is getting an oil sample checked.

I ran the combustion gas test on my Jeep 4.0 and it was fine. No evidence of a blown head gasket. The oil looked good too. Not milky.
I took an oil sample and sent it to Blackstone Labs. They identified high levels of potassium in the oil, which is from antifreeze. The oil analysis confirmed a head problem even when the combustion gas test didn't. Not a big leak, but enough to show high levels of lead in the oil, indicating the bearings were getting eaten by the antifreeze.

But I'm sure the will solve the problem