I have an 87 GT with a 383 sbc and the 5 speed. I use the radiator Archie V8 sells and an electric water pump that pulls from the radiator and pushed into the block. My fan is an upgrade.
While driving the engine never gets too hot. With 95 degree temps today I let it idle in the garage for 45 minutes and the temps get to about 200-210 and stay there. The same happens with spirited driving in these summer days. When I shut the car off the radiator sounds like it boils and the overflow tank fills up and then overflows. I cannot tell if their is actual boiling or if I am hearing water percolating into the overflow tank. As the car cools it suck water back into the radiator and I end up with an empty tank. After several days of driving the radiator will be a gallon of water low.
What is going on. No leaks were found with the long idle test. Do I need an electric water pump with a higher flow rate? Do I need a delay relay that keeps the fan and/or the pump running for 30 seconds or a minute after I shut the car off?
Probably running the pump and fan for a while after you shut down will fix the problem. The engine transfers heat into the coolant after shutdown, that pushes water out the front cap into the tank and over flows it, you need to cool the block before you shut down the cooing system. Larry
Trapped air, jack the front up so cap is gighest point and keep overflow filled. Run through a couple heat cycles letting motor sit for 45 mins to 1 1/2 hrs in between. Be sure and keep overflow full so system can keep drawing from it. G/L Ray
EDIT: You also may want to check your passenger floor to be sure your heater core isn't leaking. ( if you truly have to add a gallon)
[This message has been edited by rcp builders (edited 09-09-2013).]
I will check my cap again to make sure the radiator cap is truly "Non-vented" as Ogre says.
As far s filling I use a radiator system funnel that locks onto rear cap and allows me to add water while running and lets out any bubbles. I run the car through several cycles. I do not think air is the problem. I did re-read the Ogre section on caps and the note that the front cap is below the water level of part of the block may explain what happens and why the level always seems to fall to the same level. After the long idle test yesterday and no leaks I shut it down and let the water pump run for awhile along with the fan. No leaks and no issues. This morning I notice a large puddle of coolant under the front of the car just as the Ogre says can happen with a vented cap.
What's your water to coolant ratio, when you shut the motor down at 210 deg the coolant in the motor is going to climb above ~220 deg for a short while and if your cap is not holding sufficient pressure and your water/coolant ratio is in the right range to permit it, the coolant will boil some in the same manner that a shaken carbonated drink will when the pressure is released. I've had the coolant loss from the overflow due to a vented cap but never while the system was under pressure. Check the locking tangs on your cap and the filler neck to make sure they are not distorted causing a poor seal.
I prefered Archies original belt driven pump method. My car with a 383 automatic never got hot, even running a 4 cyl OEM radiator. I just made sure to carry a spare belt (i do anyway on most of my cars), because its possible to hit something in the road and knock it off. I can easily put on a new belt without any tools in a few minutes. I never trust an electric pump myself except maybe for a drag car thats not driven on the street.