Coolant Concerns

I'm going to be driving to East Tennessee at the end of the week. Looks like it's about a 13 hour drive. My car is getting pretty old, but running fine, except the blinker doesn't blink at the moment. As, I suppose, with any older car the fluids often need topping off. At the moment I'm having the most concerns with the coolant. About a month ago I had to refill it a bit sooner than I expected. I topped off the power steering, and checked the oil as well. The oil was way high. I had just had it changed a couple weeks before that. I was thinking that it wasn't burning/losing oil. If I had checked it after 5000 mi like I usually do I might have thought it wasn't losing oil, as having checked it last week I can tell that the level is going down. Good thing I checked it after 2000 or so miles. I guess it's OK to overfill it. I wonder if they filled it high intentionally because they know she's got some miles on her. In which case that would be rather considerate.

I remember that when I topped off the coolant I wasn't sure that I had filled it too the max level, but I figured it is good enough for now. I also remember thinking that I might think it had gotten worse if it alarms again earlier than expected, but I brushed it off. Well, sure enough, it alarmed last week just before my long trip. I refilled it, but even given my recalling the earlier circumstances I remained a bit worried. I checked for puddles underneath the car and found a large one on Friday (but it may have been there before I parked there). I checked the level and it was down, but at a time when the engine was cold (I had filled it when it was warm). This morning I checked underneath where it had been parked and didn't see much. It had been raining but it had dried some and I think I could still tell. There might have been a small patch, but nothing for certain. I then checked the level just after I got to work, and it is lower than I had left it but nothing dramatic. So, I guess it hasn't sprung a major leak. I also was concerned that it might be getting into the engine, but the oil looks fine, not sludgy. I don't think it's to the point where I wanna put oatmeal into the coolant system to plug any small leaks, but I've started thinking about it. They must have some coolant additive for this kind of problem. I guess I should buy another bottle of coolant for the trip...