Ok guys i have a 68 289 that cannot keep water in! i have a big 3 core aluminum radiator , new water pump and thermostat. the problem is, is that it is building up pressure in the radiator and blowing it out the cap until it looses enough fluid that it starts to over heat. i have a new overflow hose going into a jug but when it acts up it doesnt go into the overflow. now i have had this same issue with all 3 radiators i installed. the only thing i know is that the 90 degree pipe that is on the right of the distrib that feeds the heator has a long pipe that goes into the intake that i know restricts the flow to the heater im sure...will it cause the issues i am having? it doesnt seem as if the hoses are collapsing and tonight it cooled off and didnt overheat at all comming back into town. now i dont have a shroud either but the air movement through it feels like alot. could the thermostat be installed backwards and cause this? i put it in the way the other came out but then i had this issue then as well. Air bubble perhaps? any help would be great.

 

It could be a head gasket leak.
This would cause the fluid level to start rising almost as soon as the engine is running.The coolant would act as you describe.
Check the system with a pressure test to find any leaks into the cyclinders.

 

thanks ill check into it. but it doesnt always do it unless i get on it hard. and other times just cruising at 70 down the hwy. in town it seems to be fine unless im ideling in teraffic and it is 90 degrees and above. heck i drove 2 weeks in town with no problems until i hit the hwy. im baffeled....