87 CRX DX cooling debacle - complete stumper

[Neutrino]

Hi,
I have an 87 CRX DX with a persistent cooling problem. It gets to 5/8 readily enough, and stays there for a little bit. Then it gets hotter. Temp gets to 3/4 after about 30-40 minutes of driving in city. The freeway is not much better. Before I replaced the radiator, it would get into the red after about 30 min of freeway speeds.
I've replaced the head gasket, thermoswitch, thermosensor, temperature sending unit, thermostat, water pump, and the radiator and hoses. Every frickin' piece of the cooling system except the fan. It STILL gets too hot. I know the fan works as I've shorted the thermoswitch so it's _always_ on (which doesn't seem right).
But it seems that _sometimes_ it works almost as well as it should. Once in a while it will run at 5/8 for, say, 20 minutes of city driving. That seems a little hot to me, but I could live with it.
Any thoughts on what the problem could be? Thermostat that randomly closes? I tested it before I put it in (correctly) a few months ago. I am utterly stumped.
Minor details: manual trans, 1.5 CC engine, 400 watt stereo amp.

 

[Airjockie]

running too lean...get more fuel to the cylinders. My crx was the same way.

 

[Neutrino]

I've thought about this quite a bit and I don't understand. How does too little fuel cause it to run too hot?
And is there anything that makes this procedure any easier?
Anything I should also do while I've got the carb off?

Thanks for the assistance.
-CC

 

[Airjockie]

running with too little fuel will cause it to run lean...and a lean fuel mixture burns hotter than a stoich or rich fuel mixture...the added temps for running hotter will cause to cooling system to not perform as good as it could. Add more gas...and it will bring down the temps a lot.