Hey everyone,I have a 1978 Firebird Trans Am with the 400 Pontiac W-72 engine linked up with a Super T10 Borg & Warner 4speed. The car is about 98% original with around 61k miles on it. I had to replace the water pump, plugs & wires, HEI system, mufflers and that ugly restricting pancake cat system. More recently though it looks like I'm going to have to replace the original radiator due to an over heating issue. When I bought the car in 2011, it had been sitting with old dirty radiator fluid (probably from the 80's) since 1993. I replaced the water pump the first week I had it and flushed the radiator and engine with a hose. I've been running a 60-40 mixture of coolant, as I live in Florida which is hot and humid a lot of the time. On my way to my buddy's house who has Hot Rod heaven in his backyard....mostly old Chryslers, my car hit 230 degrees on the highway, in which I then pulled off to let it cool down. Oddly enough, in the city it runs a cool 180 degrees all day, only on the highway does it start getting hot. Now, the pump is only a few years old and there are no leaks. It doesn't sound like a thermostat issue either, so I'm guessing the 36 year old radiator is just clogged up inside. The plan is to now replace the old radiator with a new one. Don't worry, I'm keeping it a mechanical fan setup .Now with that solving my overheating issue....I have my timing currently set to the factory recommended 18 degrees before TDC. Now as an younger Hot Rod enthusiast, I've heard from older Hot Rod guys that advancing the timing, to lets say 14 degrees before TDC will yield a few extra ponies. What are your thoughts on this, will it damage the valves or any other part of the motor and do you think it's worth it?Thanks as always guys!Coming home tonight in 75 degree weather, speed around 65-70MPHCar going out today in 80+ degree wheather, speed around 65-70MPH
do you have a thermostat?? probably a 192F version in there to control the cooling systemrunning down the highway at speed.. the coolant without a thermostat will circulate thru the radiator so fast that the ram air thru the radiator will not cool it ..heat will build up till it reaches the temps you have mentioned..i don't recall if the 78 *** have any rubber flaps around the radiator that keep any air coming thru the grill going thru the radiator..on 3rd gen trans am's which were total bottom breathers.. lack of the air dam.. or a damaged air dam under the core support changed the air pressure built up under the engine compartment.. it lowered the air flow pressure in front of the radiator and raised it behind the radiator.. causing air flow at speed to go forward thru the radiator negating anything the electric fans could do.. with the air dam replaced or intact.. the air dam bulldozed up air in front of the radiator where it would flow thru the radiator in a proper direction. i used a magnehelic gauge on my sisters 85 TA.. to prove my point. thermostatic fan clutches also don't turn on until the air flow across the thermostatic spring on the front reaches 185 to 190F. when a lower temp thermostat is used.. in marginal cooling systems.. the thermostat will be wide open before the fan clutch cycles on.. it can almost never control the temps at that point. just a few ideas..blocked radiator tubes are a major issue.. so replacing the radiator is a good idea..you also might want to think about knocking out the rear most freeze plugs on the side of the block. you can then dig out any debris thats hiding back there.. then flush it out.. this will greatly reduce the run away temps.. there are issues with pontiac motors and the water plates needing adjusting to improve pumping. the tube seals also ..
Just a quick update,I replaced the 3 core factory radiator with the bigger 4 core radiator (which was used on Automatic & A/C equipped models) and its been running at a perfect 180 degrees.