When on the highway, my car runs cool. Well below 80*C, but when in town in stop-go driving it will go to about 90*C, if the temperature outside is over 65*, but never goes over 90*C. I noticed the other day that my radiator cap seal has a tear in it.

One day when in town, I made a quick run in the supermarket and when I came back out, I saw anti-freeze coming out of the top of the reservoir - where the hose comes out, but it has a puncture. I was once told that if my cap seal was damaged that this would happen. Is this true? It has not leaked since then. Could this be why my gage fluctuates so? Perhaps a faulty thermostat? I think I will at least change the cap and see if this makes a change. I have to change out my green coolant anyway.

Thanks.

BTW - also an oil question. As my car (and others) warm up, oil pressure typically lessens. I would like for my pressure to be higher when the engine is hot. Whats better for the best pressure when it is hot? 20W-50?

Thanks!