My home made pressure tester plus AST q\'s

[Grizzly]

I forgot to say, if you do bend the Tabs on the Cap do little adjustments and keep trying it until it feels Tight, if you go too much to quick you\'ll overshoot and it won\'t go back on without some messing about.

[RemarkLima]

Thanks again Grizzly, always appreciated (along with the rest of you guys of course!!!).

Good idea about seeing if it weeps at all, makes sense to me. As I\'m sure the "top" seal is fine, no leakage around there but then that\'s zero pressure as well, so it\'s just to see if the lower seal is any good...

Just out of curiousity, do you run an alloy AST or the stock one?

Anyway, work as usual this week (while also trying to source a lower boot for my gf\'s Figaro) so looks like it\'ll be the usual weekend fun

[Grizzly]

I have a Stock one at the Moment, I had an Alloy one but that got swaped back for exactly this reason.

I know what your saying about the Top seal being ok but i\'ve never had a problem with that seal myself, the reason i bent the tabs over more is to get as much load on the Lower seal as poss, i know it doesn\'t move allot but its helped me before.

[banned advertiser]

So, just so I know I\'ve got this the right way round, with the cap on the AST I can pressurise the system to 13psi (as per the pressure cap) and this should pressurise the entire block, matrix, rad, turbo\'s etc? As the pressur goes via the rad, to the AST, through there into the lower hose and into the block and off from there???

I did notice in the FSM they tested the system on the AST cap, rather than the filler cap... And then pumped it up to 20psi, to test for leaks etc...

I\'m sure that should have pushed water into the engine if my water seals had gone, right? I\'ll get it up to 80C as well and try again, at least it\'ll keep me warm this time

You should be using a .9 bar cap.
One reason we dont sell ally tanks, as we hear complaint of not holding pressure.
Stock ast approx £90 inc new cap
http://www.rotaryart.uk.com/acatalog/New_Mazda_RX7_3rd_gen_engine_perf_tuning.html

[RemarkLima]

Cheers Gary,

I\'ve been using .9 Bar caps (or 13lbs) and I have a unexploded Mazda AST to try first but if it is that I\'ll probably just get a new one to be safe.

Just the FSM says to test the system with 20psi... But on a 2nd look it says on the rad filler neck (so the usual filler point, not the AST). Which comes back to, how is it supposed to hold 20psi??? Surely it\'ll go down to 13psi and hold?

[RemarkLima]

Sorry, just realised that should be for a 1.3bar pressure cap right?

[ianelvar]

They\'re testing with the tool connected to the AST, and the filler cap can\'t lift, so no pressure should be able to escape.
You\'re right, using the tool on the filler neck means the AST cap will act as a safety valve and release some pressure once it gets to 13psi. You can hear a gurgling noise when the do release some pressure. I\'ve had some that lift as low as 5psi!

[Grizzly]

Or more to the point if the cap is leaking it will show up if you use the engine side rather than the AST to pressure the system.

A word of warning don\'t go above the cap rating if for some odd reason its stuck etc.

[RemarkLima]

They\'re testing with the tool connected to the AST, and the filler cap can\'t lift, so no pressure should be able to escape.

That\'s what I thought but look at the pic again, it\'s on the filler neck so the 20psi must be for the 1.3 bar cap.

Which means it\'ll also test the pressure cap, just need to see if I can be bothered to swap back to the plastic AST in the cold and dark or wait until the weekend

[RemarkLima]

Right ho, just changed the AST back to the plastic mazda jobbie (the one I got from you Robbie as it happens ).

Seems to hold pressure properly but I was fecking freezing by then some come in for a bite to eat and a cup of tea! I\'ll let you know how it goes!

[RemarkLima]

OK, so what happens if the cap isn\'t sealing properly? Does the coolant push into the expansion tank all the time? And then you loose loads?

But at normally running temps even water shouldn\'t boil, right? Or will it still boil in places and it just depends where the sensor is?

I think it\'s time for yet another cap and a more accurate pressure gague!

[Grizzly]

If you can hear it boiling its a good sign your water system is not sealed, the theory is that water under pressure boils at a higher temp, if you have a leak it will boil at Operating temps (more obvious when the motor is under load i.e. Driving)

Cap wise, in theory if the cap was leaking it would push water out of the system as it expands on warm up, BUT!! If that was the leak why would it be drawing air back when it cools?? (unless the ast-expansion tank pipe is not air tight)

[RemarkLima]

But isn\'t the standard running temp 80 - 90C? So it shouldn\'t boil even at 0 pressure and just water???

Or is there hot spots that will boil, just not near the sensor?

I\'ve been swapping caps around and I think I put a really cr@p one on which continued to throw water out of the expansion tank and it kept over flowing... I\'ve changed it back and it\'s been OK again, but time for another new cap I think.

I\'m not sure if it\'s drawing air back in, but it could be, I\'ve put a clip on the AST end to the expansion tank, so that should be fine but not sure about the other end... I may just replace that length of hose, but that clips onto the expansion tank and then there\'s a pipe going down into the expansion tank right?