Consuming Coolant slowly, no leak visible.
OK here is what is happening, and some details and history.
2000 Ford Taurus SE, 3.0 L V6 Vulcan. 245,000 Km now.
[ Yes, it's getting on in age and miles - but still runs GOOD, well maintained ]
Is slowly consuming coolant, with no leak visible, no steam seen, no smell.
It has been slowly consuming coolant for about one year now I would say.
I think it is slowly getting worse. I am continuing to monitor closely and adding as needed.
At this time, in 300 Km and 3 hours of highway driving it drops now about 1 inch in the reservoir bottle. I estimate that is just under 1 litre lost somehow in this amount of driving.
This mid-august, it was in to the Dealership for other regular maintenance, and I mentioned this slow coolant consumption to the Service Rep. They had the mechanic do a pressure test, and said it held pressure for 30 min with no drop. And advised me to just continue to monitor and keep adding for now.
Car still runs fine, for it's age and mileage, pretty good still.
Oh ya, the Timing Cover Gasket had a leak several years ago, and was done. And a new Water Pump, and Crankshaft seal was installed at that time. That was a problem that got worse until I HAD to fix it - leaking too much, and coolant dripping down onto hot CAT Convertor, and steaming up into the engine compartment, and then that steam smelling and getting sucked into the cabin by the ventillation system at the stop light.
I digress ...
I read some other posts and threads with similar issue - slow consumption.
They mention possible HEAD GASKET leaking, and possible car burning the coolant in the the combustion chamber and out the tailpipe.
They mention possible SLOW LEAK somewhere and evaporation - so not easy to see and find the leak.
They mention possible cross leak into some other system - like oil or trans oil.
One suggests "chemical dye test" ... mechanic adds chemical marker of some kind into coolant - and that shows better where or how the missing coolant is going.
One suggestion is take samples of various oils for test. Check engine oil for change in colour (milky colour?)
If it is being burned in the engine, is there an emmission test that will show it ? In the exhaust gases? Can one SMELL it burned in the exhaust? Just my ideas.
P.S. For first time ever, the oil pressure light flickered a little, one evening, after a highway run, when idling to unload a few things. Pulling up the REVS a little made it go out. So just indicating lower oil pressure at idle. Never seen again since. No issue I think not ... but thought to mention this anyway.
Thanks in advance for any advice or help.
No major problem yet ... but I can see something coming - given that the rate of coolant consumption is slowly increasing.