Well, I finally nailed it down. Head gasket or block/head crack. It must be a very minute breach. My wife came home today again with it spewing coolant out the overflow but the gauge at normal temp. So this time, instead of topping it off I left the bottle almost empty and revved the engine to 2000 RPM for about 30 seconds straight while watching the fluid level in the bottle. It began to rise and steadily rose about an inch. I left off and it dropped. Then I brought the RPM's back up and held it there for awhile longer and began to see tiny bubbles continually coming up through the coolant. I couldn't see them before and I think that was because with the bottle full, they dissipated before they reached the top of the bottle. There are exhaust gas test kits available for around $50 but I passed on that since I think I've identified the issue.
Therefore, as much as I am not fond of 'liquid fixes' we went and bought a bottle of Bars Leak Head Gasket Sealant #1111 to try. I read on several car forums about a number of people with similar issues using this with success, so I figured for $20 - $30 it was worth a shot. It is supposed to be a permanent fix. What is interesting is that when we read the bottle, it specifically states 'your car is a good candidate for this product if it can idle for 20 minutes without losing coolant or overheating' and her car does exactly that. We just need to buy some time. Since I joined the ranks of unemployed this year due to our lovely economy, even if this gets us through a few months that would help. Then we can hopefully better address the matter once things return to normal. It's been a day and a half with the Bar's Leak in and so far it's holding, at least on the 20 minute drives to her work and back. Guess we'll see!
Thanks again for all your effort. Hopefully sharing this experience will help others more quickly locate similar issues. I've been working on cars wince I was around 14 years old (1974 or so) and I never seem to stop learning new things!
Hi John, Thanks for sharing that experience. I believe that there is a good chance the leak will be sealed by the Bar's Leak. It appears to be a small leak which made the diagnosis a challenge. If anything further occurs do let me know. Thanks, Roland