CantGoStraight

I'll try and make this simple for you (and all others with this issue). The "Recovery tank" you guys call it the overflow resivoir is designed to allow the coolant system to "Recover" the coolant that expands out of a hot coolant system into this tank so it maintains the proper level when the engine cools down. The tank has a full mark on the dipstick that it should be close to when the engine is cool. The tank should "not" be much higher than this mark when cool or the possiblity of the "recovery" tank overflowing on to the ground when the engine is hot. You need to determine why the coolant is moving from the cooling system to the "Recovery" tank and not back to the cooling system when it cools. You never said if you corrected the hose from the AST to the "Recovery" tank issue. If you didn't fix this then the caps won't make any difference. If you did fix the issue then you need to get a system pressure tester and find the problem.

RX7 allnight

i tested the tube from the "recovery tank" to the AST and it was fine. i pressureized the system for over night many times and it would drop very little. but no visbale leaks on the ground.. i used a clean peice of cardboard each time to see if water/coolant leaked. no leaks. so unless its a small pin hole air leak somewhere in my system(hoses's/rad)its my coolant seals. (before this i changed ALL my engine heater/coolant hoses)

Silverstone

All I can tell you is that I had all the same issues you had and they all changed overnight when I switched to Evans NPG+ waterless 375F (@ 0 pressure) Coolant.

May have been a pressure leak issue but doesn't matter with Evans. It doesn't need ANY pressure to work perfectly and never overflows into the overflow bottle. Problem solved. It may not work for you but it did for me. Just my $.02

The nice thing about this approach is that it solves multiple issues all at once without trying to guess at which one is the cause.

If you want to know how to switch over to it, PM me and I'll give you the low down. It's a little tricky.

CantGoStraight

The only issue running this coolant will do is prevent boil over. The system still has to be in working condition to work properly, I.E. your coolant still has to be able to move into the recovery tank and flow back into the engine when cool. I too use the Evans but more for the ability to run zero or low psi on the system without boil over, but mainly for the lack of water and prevention of corrosion and electrolosis. Evans will not fix a non-functioning system.

Silverstone

I guess that is true. Honestly it is still a mystery to me what was happening with my engine/cooling system. As I said, I had all the same issues as the OP (switched caps, pressure tested, stood on my head ) and then it stopped when I switched to evans. Judge how you will and draw your own conclusions. There may be an underlying problem that will surface later but for now (and the last year) it is solved.

Just a thought: If the evans solves boil-over then doesn't that keep it from entering the overflow tank to begin with? So doesn't that in turn solve the problem of the coolant not returning to the system since it never left? Yes there might be some other problem that the Evans covers up, but who cares? If it is serious (like an o-ring) this may get you some more mileage out it before rebuild and it is not too serious like a leak preventing return of coolant from overflow, then this allows you to operate until you eventually can find the leak or have your whole cooling system overhauled.

CantGoStraight

I was in no way making a judgement call on your post. It's great that switching your coolant over to the Evans solved your problem. I was just pointing out that the switch in no way fixes a coolant system that is not working properley, that and it would be expensive in the short term to use as a troubleshooting choice. I run my system with zero pressure withtthe exception of any maintenance that involves draining the coolant, then I will run the stock cap till I'm sure all the air has burped from the system. Then back to zero psi.

Silverstone

It's cool man. I wasn't judging you that you were judging me and BTW I agree it is somewhat of a temporary fix. I actually run a 7 LB cap to keep water from finding its way in over time. Not a DD for me so I'm content to just drive it and not worry about it if is not causing me any problems.