I know tbe line coming off the AST tank feeds the overflow tank, But where is the line that sucks back coolant into the engine from the overflow tank??

 

same line ... make sure no leaks. cap at ast should have a central check valve that can be easily pryed open ... this is how coolant is drawn back into the cooling engine aft shutdown.

 

Can this line be replaced without replacing the entire Overflow tank ? I am wondering if it just pops off where it attatches on the top of the overflow tank or if it's mounted in there for good ? Anyone know ???

 

Also, when does coolant get sucked back into the system from the Overflow Tank ?? Does this only take place after the car has been shut off ??

 

Yes, the line can be replaced by it self, just make sure there are no kinks in the new line when installed. Kinks and leaks will prevent the coolant return process.
The coolant only returns to the system during the cool down process when the coolant contracts and creates a slight vacuum. This only happens after the car is shut off.

 

I notice coolant spill after shutting off, I check the overflow and it's empty???I just fill that up couple days ago... I fill it up and same thing happen after shutting off, but don't know where the leak is coming from???

 

Same thing happens to me, and i have pettit AST. However i think that the cap might be faulty because, I can usualy see the dried trail of antifreeze on the sides of AST. When i was under the car i checked the hose, and it looked ok to me. So I think it might be the Cap.

 

Could be the cap, could be the portion of the neck on the AST that seals on the cap ( that's where mine was bad ), could be a pinhole in your system not letting it create a good vaccuum. Tom

 

I am also getting cooling problems now with my RX7, and I cannot work out where the problem lies. My filler cap needed replacing a couple of months ago, which I replaced, and now when the car is running everything seems fine, the temperature guage never goes above half way on the guage, but when I park the car, I see a puddle of coolant appear by the front wheel axle, and when I look at the coolant the filler neck is full but the coolant in the overflow bottle has gone down from the Full mark to the low mark, I think I am losing about 1/4 litre of collant a day after driving 100 miles. I am topping it up daily and always lose approx. the same amount of coolant, When I stop the car and turn the engine off the fan automatically cuts out as well, is this normal? have I got pressure problems, sticky thermostat??anybody had this before? got any ideas??