My 78 Has a 351M/400 that has the 400 crank and pistons and it has been bored 30 over and crank turned 10..I have added a new High Flow Water Pump and High Flow Thermostate and a new Radiator and in traffic and red lights the temp runs about 215 some times up to 220,,,is there anything else i can do to cool this 400 Down???I also have a fan shroud.The Radiator is a 3core should i go to a 4 core?? and electric fan??

what temp does the thermostat open at?
then put a lower temp thermostat in.

i thought a high flow thermostate did not have a temp that they would open at,the thermostate and water pump both are High Flow..i thought they would be open all the time not just when they got to a certail temp.

Your thermostat is set to open at 160, 180 or 195. Since you have a 78 you should use a thermostat set at 160 or 180. Have you flushed the system real good?? Since you have changed the motors specs from stock put the four core radiator in to. Before you do any of that are you using the stock temp gauge and sender or a mechanical gauge and sender?? Check them to see if they are working correctly or not.

I have flushed the entire system out when i added the high flow water pump and high flow thermostate.i also cleaned it out all over again when i put the new 3core radiator in last summer,,i still have to but a 4core radiator,,i also have to buy some end liks for the front sway bar,one on the right side is broken..

have you checked the gauge and sending unit??

yes,, when the motor was lowered in, i replaced the temp gauge,battery gauge,oil pressure and snding units and i know that a bored motor will run warmer but my truck runs 200 to 220 in traffic and red lights,,

i also have used the water wetter and that does not help at all and also had thetiming checked and it was set on 12 or 15 so that was lowered down to 9 and it slowed the motor down but not the temp

Have you tried using the old thermostat? A friend of my dad had almost the same problem. He built the motor and used the high flow pump and thermostat It would run hotter than normal until he put the old thermostat back in. Two weeks later the head gasket blew.

well i already tried that and it ran hotter, so, i put the high flow therm back in,the motor has been flushed,,i guess the only thing i can do is to buy a 4core radiator and a elec fan and see how that does

One last idea try running it with out the thermostat and let me know how it does. Does it have an auto trans or ac??

I have a 78 with a 460 and it did the same thing. the culprit... the backing plate behind the water pump was rusted out. and they don't always sell them with a new pump. i got mine out of a 429 sitting in a friend of a friend of a friend's shed. plus the guy at the parts place might of given you a pump for an 88 pump (reverse flow) it happens. check it out.

well the water pump is a high flow water pump and it was bought through Zegs performance parts and it is the right water pump for the motor,,i had the motor rebuilt and it had a regular water pump on it and it was really running hot then changed it to the high flow water pump and added a high flow thermostate and it still runnde hot and driopped tio a regular 185 thermostate and it runned hotter so i put in the high flow thermostate and nopt had time to change the flerx fan for a stock fan yet to see if that will help.

oh yeah i forgot about the fan! I took the solid fan off the 429. it has a 2 or 3 inch spacer and longer bolts than the stock one. I have a regular replacement water pump, the stock 3-core and a 195 thermostat and the guage reads 185 all day. by the way the hotter your motor runs the better mileage u get and if u get too low of a thermostat or run without one (bad idea) your cylinders will wear out quicker.