If you remove the thermostat and it doesn't overheat, and stops boiling

Good, go to the car show.

But don't plug the overflow tube. It is their to relieve pressure. Plugging it may overpressurize the radiator.

Radiator cap regulates the pressure, if it's not working the system wont be pressurised and the water will boil at 100 deg C instead of the higher temp you get by running it under pressure.

y does it matter?

Is the radiator cap in ok condition? why is it over heating? Did it only start once you changed to the civic radiator?

dont do that unless you want to really break something

thanks guys.. it is boiling and not just the sending unit.. i have a overflow nipple at the top of my rad and it is blowing a lot of steam..
Im thinking of removing the thermostat and plugging the nipple and seeing if that helps.. the cruise starts in 3 hours so i have to work fast...

yea, scott is american. Oops, the kind that uses metric everyday, forgot about that.

Ok, plain water boils at 100C/212F. But with a typical 1-bar pressurized radiator (like a Datsun radiator) it raises the boiling point. The engine is not hurt by high temps as long as the coolant doesn't boil out. And it won't if it stays under the (raised) boiling point.

200??

I really hope you are talking farenheight O_o

hey scott congrats on getting it on the road.

Gauge reading 3/4 is not uncommon. Sometimes it is the sender or even gauge.

Yes, check the actual temps first thing off.

Even if it is running 200 degrees, if it never goes over 3/4 then you'll be fine. With a 14 psi cap, you can go over 212 without boiling over.

before you do ANYTHING go get your local radiator shop to test the temps before and after your radiator.

Quite a few years back I spent a month replacing everything in the cooling system for a B310.

Turned out to be a dodgy sender unit. Temp was actually fine.