Triumph Repair: TR4A Overheating, blown head gasket, head gasket leak

Question
Replaced waterpump, all hoses, had radiator checked by radiator shop, flushed system, replaced timing chain, new radiator shroud, 3 new thermostats, adjusted timing, richer fuel mixture and added electric fan. Car runs fine for about half an hour, sometimes longer. It appears to build pressure in the system eventually forcing water out the overflow. I show no signs of white smoke in the exhaust, no water in the crankcase. No overheating until it loses water out of the overflow. What can be causing the pressure to build in the cooling system?
Thanks,
Larry

Answer
Hi Larry,
Your assumption that it is not a blown head gasket because you don't see white smoke or water in the oil is very wrong. The proper test of a head gasket leak is to put the dye in the radiator to see if it turns color ( the dye is available at most any auto parts store) or you can use a CO/HC test machine to sniff the radiator fluid for signs of CO.

A 100% correct test is to get the adapter to replace a spark plug that adapts a compressed air hose to the engine and place that piston at TDC and put the car in 4th gear and the brake on and connect the hose to adapter. This puts line pressure (125 PSI to 150 PSI)in the combustion chamber and is a 100% test for valve leakage for intake or exhaust valves. Then you open the radiator cap and watch the fluid level. This test will spot a leak so minor that it does not even show up at high loads and high speed. All four cylinders must be tested.

Any of the above three tests are valid tests for combustion chamber leakage for a gasket or even a minor crack.
Howard