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Thanks to the great resources successfully did coolant change with Pentosin Pentofrost A2 and burped system.
I do need help to figure out how to remove this AST cap. I can twist it loose and lifted up the lever, but seems to be fixed in their pretty tight and I didn't want to break it. Can't get it off to check the spring. SEE ATTACHED PICTURES.
Air separation tank cap - twists loose but can't lift off AST. I did lift up the lever when I attempted not reflected in picture.
Searched the internet and didn't find out how to remove it from the AST itself.
If you lifted the lever and turned the cap counterclockwise it should lift out without much, if any, resistance. Something is wrong. Off-hand, if you have a compressor, you might pinch off those lines so they don’t drain all your new coolant, remove the ast and put compressed air to it to try to push the cap out without damaging the neck.
I have one of those caps on an antique Chevy and never had any issues. But personally never liked them for the RX7. They just look wrong/out of place under the hood to me. And that’s a 16 psi cap. I prefer to stay with my .9 bar (13 psi) caps.
Found out I have a pettit AST. I read other posts on the internet including RX7 specific forums, and identified that I need to push straight down on the cap ( firmly) and turn further to the left before the cap would clear the outer neck ridges. A total rotation approximately 130 degrees did the job.
For the newbs like me, there are 2 stages:
1) turn left releases the cap from the sloped ridge that loosens it (about 45-60 degree turn). This was where I thought it should come off as it was loose enough to jiggle the cap.
2) then ensure you are pushing down enough to compress the cap an additional 2-3mm and turn left some more. should feel minimal friction just like when you turn the filler neck cap. If you are feeling a hard stop, compress DOWN more, DON'T twist harder without pushing down more firmly. Should be able to take off after turning past a palpable point where the Cap is loose off the neck.
I do wonder if the fit and design of the PETTIT AST tank outer neck with any radiator cap, similar to what I experience, has led others to strongarm the cap such that it twists the neck, leading to the warping issues commonly described. But I am a newbie and only have an N = 1. This is only my experience, and not to restart a thread on Pettit AST quality again.
By the way, I replaced the cap with a Gates 31527 without lever which I felt is better made compared to Motorad T-13 which is what they stock at Autozone, Napa, and Oreilly. You could feel the heavier gauge metal in the heft of it and the spring just moved smoother and compressed more progressively.
