General overheating Q and watercock diameter

[bcar240]

This is not really a 300zx specific prob, but is my first time encountering an overheating problem on a car (have been lucky) so am trying to narrow it down. Was driving my z31 around the other day and noticed the temps started to climb, never got to the top but was only a notch or two down on the digital cluster bar graph. Pulled over and checked under the hood and the top radiator hose was piping hot (too hot IMO). The lower hose and the few places I could manage to snake my hand touch the radiator were basically ambient temp. The heater worked and the air was scalding hot, again I think even too hot. Overflow tank was WAY over the max mark due to coolant expansion, it got sucked back into the system as it cooled and went back to the regular level. I'm guessing it either has to be the thermostat or a blockage in the radiator, I will replace the t-stat regardless, but are there any good ways to tell if there is a rad blockage? The car only has like 130k on it and was babied for the first 100k by the first owner, so I'd be a little surprised if it was badly gummed up. I'm also assuming since the heat works it means the water pump is pumping ok, am I on the right track here?

Second z31 question. Does anyone happen to know or have a watercock lying around to measure what the ID is for the heater hose connections? Looks like 1" OD from my trying to measure it, so probably 3/4" ID? My valve is shot and I am just going to get a ball valve to rig it for a while until I can score a replacement so I can turn the heat on and off more easily than the ziptie method. I am trying to get all the cooling system parts ready to go so I can do all the work at once, so I didn't want to pull the old one off yet.

[evildky]

I'd guess the thermostat but keep i mind this is a 30ish year old car. Just because it has low miles and was papered doesn't mean sediment hasn't formed and collected in the radiator. I think the heater hose is closer to 5/8" IIRC but I think I'd sooner zip tie until I find a replacement than to d!ck with it twice.