My car's cooling system is still clinging on to the edge of sustainability. For the last two years at least it ive noticed the coolant in the header tank will begin to disappear after a week of driving, quicker if the driving is spirited or in 80'+ temps. I have to keep a close eye on it or it will eventually begin to suck air annd no longer cool, I will get a warning that im on the edge as the water temp climbs from above the 160' notch to hover near the 220 mark, at that point I have to turn off the AC or turn on the heat to keep it down but that only makes it last another 10 miles. This has only been a repeatable problem when the outdoor temp is 85'F + and or I do some sustained 80 mph cruising. A few weeks back I drove to Monterrey, ca from Sacramento and back in 50-60'F temps and i lost very little coolant.
In this video My car is fully warmed up after a 8 mile drive around the neighborhood in 82' temp with the A/C cycling all the time. The gauge reads between the 160' notch and 220' Notch which is typical for my car in this ambient temp. With my trusty infrared Temp gauge you can see the water temp coming from the radiator is about 170' and the water leaving the thermostat to the radiator is about 200'. I also read about 200' at the back of the cylinder head where the temp gauge sender is.
Last I show my overflow bottle that installed back when I began to loose coolant and i wanted to track if it was coming out of the overflow tube of the header bottle. This is where all the coolant exits the engine, not at head gaskets externally or at any cooling hose junction. The car leaks oil but never coolant.
You will note that there are alot of bubbles coming out of my over flow bottle which was empty when I set off this morning too.
Header cap is pretty new and is the forth one I have bought over the years, I have tested the cap with a pressure tester, it is a 15lb cap that releases pressure just over 15psi.
Header tank-cap seal surface is clean and smooth, cap feels tight and secure when on the bottle. My coolant system is simply running far more that 15psi when hot and at pressure.
I believe I have a small leak between a combustion chamber and its surrounding water jacket. When hot enough it opens and the higher pressure combustion pressure is pushing into the coolant over loading the system That is the bubbles you see in the bottle. I have zero coolant in the oil and zero oil in the coolant. I have had the oil analyzed for coolant traces from Blackstone Labratories, Sodium and Potasium were higher than normal but not conclusive as ethylene glycol.
Im waiting on a kit to arrive that tests for exhaust traces in coolant for the final conclusion, Meanwhile check out the video and see if you have any more ideas.
http://youtu.be/olcviBA1GvI