Mate i just bought a totally stock 1200 4 speed sedan From Beachworth about half hour south of Albury Wodonga The victorian border. and drove it around 1200 K's To Armidale Northern NSW with 5 13 inch rims with tyres on them 4 in the boot one in the passenger front floor and a packaged up front windscreen across the back seat and it stayed on normal temperature all the way except it rose a tiny bit up hills to be expected but dropped as soon as i would reach the top. They are a legend car this one has oil leaks to and was missing over about 100 k's. So i don't think you'll have any hassles as long as your running coolant and you've checked all other vitals. Trust the Datsun they are legends.