I had a bad coolant loss problem in the 85GSL, about a quart every 200-300 miles, no signs of water leaks, no white smoke, no starting problem, no white stuff in filler pipe. Put on a new cap from Mazdatrix ($12) and it seems to have solved the problem. Lots of japanese looking stuff on cap, so I assume it's OEM. Also, it says 0.9 ATM, so that's interesting.

Incidentally, I setup a ghetto cooling system pressure checker as follows: the plastic Prestone 5/8" tee in the lower heater hose on the passenger side down low (I put these on every car and advise the same), a plastic 15PSI garden pressure regulator from Tru Value ($7), a 50 PSI dial pressure meter (I had from some household work) and some plastic fittings and hose to hook to the street bib. I cracked the bib to get 20PSI on the meter (the cheapo regulator only works well when water flows), shutoff the bib and watched the presssure drop off in about a minute. Since there was no water evident, I figure air leaked out someplace, probably the rad cap.

Haven't tried the ghetto pressure check since I got the new rad cap, but I'm not losing water, and when I let the car cool down for 2 hours then crack the cap I get a satisfying pfffttt, indicating it's holding pressure good.

B

 

cool idea. You should make a simple drawing or maybe take a few pics of this neat-o device so that others can use this idea.