Finally after three years of building,started the engine...first go!
coolant temp to 120c and blew bottom hose off.no blow by on cap 3ltr capri rad.what do you think?blocked rad,came from scrappy.can you clean it properly or new rad?Anyone know the size width/height of polo rad?

Might be worth trying radflush or speedflush first, got to be cheaper than a new radiator. I used it ages ago on an Escort and it even got the heater working better.

What engine are you using? it could be as simple as an air lock. May be worth taking out temperature sensor and filling cooling system until water runs out of sensor hole, refit sensor and try running engine, may also be worth changing thermostat , could be stuck

Kill or cure, if its sat around for a long time try battery acid, it beaks the calcium down and is free ! Blocked radiators feel heavy, was yours ?

cheers guys,tommorows yet another day
let you know.

I've just had similar hassles with mine.

I presume you checked the engine over during the build? Is there coolant flow through the engine? Does the water pump work? Thermostat ok?

Is the fan working (if not just a basic fan)? If its electric it'll be obvious, but for viscous fans - run engine until hot, switch off & check fan is engaged.

Have you got access to a cooling system pressure tester? Might be worth checking in case the head gasket is on its way out.

All okay?? I'd follow the 'bleeding advice above. If it starts to overheat then its likely to be the Rad - which you say came off a scrap Capri. Forget radflush products - take it to a specialist & have it recored.

Yours,
Swizz...

P.S:- Learn from my lesson! My engine always ran on the hot side. I checked all the obvious stuff, even removed the 'stat & replaced the water pump. I flushed the system through and the rad seemed clear enough. In the end I just tolerated it thinking that the gauge or sender might have been inaccurate. Wrong!!!
My bottom hose blew like yours, but on the M60. After a new hose was fitted the head gasket blew. With a new gasket it STILL ran hot. In the end (even though its flow seemed ok) I took the rad to a specialist. For £50 he replaced the core (so its basically a new rad - but a lot cheaper) and the problem was cured.
After checking the basics I should have changed the rad' much sooner as it obviously wasn't cooling sufficiently. The hose & head gaskets needn't have gone.