Coolant Problem - Not Sure
A few first steps:
- Make sure the tube connecting the radiator neck to the overflow is not clogged and holds suction. (I hook a vaccum pump up to the hose with a clear section of tubing and see if I can pull fluid back to the clear section and hold it steady for a while under suction.)
- Your radiator cap is probably bad and its time for a new one. If it won't hold pressure properly, it will leak as you described and your overflow won't work properly. (Because the system isn't holding pressure properly.)
- I'd expect your problem to make the temperatures go up, not down. Maybe you also have a bad thermostat at the same time. I'd suggest starting with the radiator cap, see what happens, and them move on to a new thermostat if the temperatures stay low.
The coolant only overflowed once when I got the car back to the house, and hasn't done it since. I've tried filling it back up, but I don't think I'm doing it right. When I open the bleed air screw on top, with the engine on and off, no fluid comes out, so now I'm not sure how much air is in the lines. I am able to take off the bleed air screw on top and look inside and not see any fluid.
I'm going to have to check what thernostat is in the car. It was my dads before he gave it to me and he did some things to it when it was having cooling problems way back when, I think he put a 160 degree thermo in there. Plus, it's been overhauled, so I don't know if the mechanic changed it out.
Where exactly is the temp sensor located? Would it read a low temp from the coolant in the radiator even if the fluid isn't circulating?
The coolant only overflowed once when I got the car back to the house, and hasn't done it since. I've tried filling it back up, but I don't think I'm doing it right. When I open the bleed air screw on top, with the engine on and off, no fluid comes out, so now I'm not sure how much air is in the lines. I am able to take off the bleed air screw on top and look inside and not see any fluid.
On the LS1, its screwed in to a head. Not sure about the LT. It measures the coolant in the engine. (Any measurements in the radiator would be weird because that's where a temperature change happens.) If you have a low temperature, that's usually a sign that the thermostat is stuck open and you have too much coolant flow.



