Re: 4.0 ranger antifreeze in exhaust
I'm unsure about the vacuum, but with 190K I wouldn't rule out a head gasket. It might be so small that when the engine is cold or hot, the area of say, the head gasket, is bad, the temperature either opens, or seals the small leak.
One thing you can try, is add UV dye to the engine coolant (you'll also need a UV bulb and a trouble light of course). After a few days of driving, check in and around the engine compartment to verify there is no noticeable leak. A small amount of coolant leaking onto a hot engine block will evaporate - leaving some of the dye behind.
I would stay away from stop leak products. If you notice a leak, then it's knowingly too big for any product to fix. Besides, some coolant stop leak products can thicken the fluid, causing pump problems, etc.
You can check the best you can, although it's very unlikely an exhaust manifold bolt broke off and somehow damaged the block internally to affect a coolant jacket. One can't rule anything out these days. I'd still do a UV dye test and that might help you better narrow down the problem. If that doesn't sort it out then I would tear the top end off. It's a better option than being stranded on the side of the road with a trailer.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!