Or actually had something I suspected confirmed. Engine was running fine for a while, then I stopped for a traffic light and the whole front of the jeep was enveloped in a cloud of steam! There was a pinhole in one of my heater hoses that sprayed coolant all over the engine compartment soaking everything. The temp shot up to 230* about instantly. I got off to the side of the road and shut it off. After it stopped spewing coolant and settled down to just a wisp of steam, I opened the hood. The hole was almost invisible after the pressure subsided. I put several turns of electrical tape around the hose and left to cap loose after topping it off with water to get it home. Of course, that didn't work too well either. This engine runs at 210* under pressure and without the pressure, it boils quickly. I got it home just as it cleared 240*!

SO, the radiator cap is a critical link in keeping this engine cool and any reduction in pressure can allow the coolant to boil and the resulting steam can destroy everything. I forgot to mention the coolant reservoir was bone dry because the cap vented the steam into it and blew it all out.

After replacing all 4 hoses and refilling the system, it runs perfectly at 210* and stays there. The cap was new about 4 months ago. The thermostat still functions and the cap holds 18 psi.

 

Good info. So now we need to install a cooling system pressure gauge to monitor it. lol Probably more accurate than our temp gauges.