cooling system

my '58 Chevy SB 283 wasnt running right so i started looking for the problem. it turns out that i needed to replace the timing chain. i ordered one from Jegs and I installed it. Great the engine turned over and started. now my problem is that i ran it for no more than 3-5 mins and the temp went up over normal and the radiator started steaming out the pressure release on the neck. could this be the result of a faulty rad cap? i read that that is what keeps anrifreeze/water from boiling. also i saw on some T.V. show that there could be an air pocket or something...? that was on a brand new engine though. oh yeah the rad cap hasent be replaced in probably 12 years or more. could something that small be the problem? anything will help thanks.
mike

How long ago was it when the car was running?

Did it have an overheating problem before?

How does the lower radiator hose look? Could be sucking it closed.

thanks but it was all because of the cap. went to kragen got a new one and its all better.
Mike