=A0 =A0 I got little help from the Honda newsgroup, and I know these two
> groups are much better, so I'm hoping that there are some helpful Civic
> owners here who can help me...
>
> When I had the oil changed in November, I was told they had to add
> "quite a bit" of coolant to the reservoir. Since the car came from NM,
> with a spotty service record, I had hoped that it was simply not topped > off ever.
A used car with a spotty service record is, well, a risk. Hopefully you got it for cheap.
Now, three months later, with only moderate driving, I see the
> reservoir is virtually empty again. I don't see excessive white smoke in
> the exhaust, or smell antifreeze in it - although I haven't sniffed it
> specifically for that, yet. The oil looks fine. I don't smell coolant
> inside the car, either. It would be hard to spot a slow drip in this wet
> Winter weather. How common are internal head gasket leaks in this > engine,
> as opposed to slow leaks in the reservoirs?
With almost any engine the chances are greater that the leak is somewhere other than a head gasket.
> Followup: I took the car to a local shop today. They do free pressure
> tests (I gave them $20 anyway). No leaks, including the cap. Unless I'm
> missing something, it has to be the #@!@# head gasket, right? Assuming
> it's going straight to the exhaust and not burning much, how safe is it
> to leave it alone?
Not safe at all. Inspect all hoses, plastic connectors between hoses, heater core connections, radiator tank & hose connections carefully for any evidence of dried coolant.
A pressure test is not a very good test imho. After doing the above you should have an exhaust gas test performed. Also, is there any bubbling in the expansion tank or forced expulsion of coolant? Does the temperature gauge suddenly drop after the car is warmed up?
Any suggestions?
See above, keep looking and find the leak.