Coolant system experts question?
 

Okay cooling system experts here is my situation. I seemed to lose small amounts of coolant last summer and it started to overheat. I replace my radiator, water pump, thermostat, AST and coolant caps. What I discovered is that reason I kept loosing coolant out the overflow is because the AST cap leaked and the it boiled over due to lack of pressurization of the system. The car runs beautifully by the way. I do not see white smoke or coolant odor in the exhaust at start up.

So yesterday I rented a pressure tester. Caps are fine. And when I pressurized the car it did not drop over 5 minutes (per the manual). I left is on over night and it dropped down from 13 PSI to 5 PSI. Is that normal or should it remain pressurized all night?

I then put the pressure tester on and started the car from cold to normal operating temps. The guage needle did not pulsate or go up quickly (indicative of seal leak). However it did slowly rise to 25 lbs (172.35 kPA or 1.72 BAR)!!?? Is that normal?

So does this mean I need a rebuild?

No one with a comment?

Have you done the "Champagne Bubble" test?

Well......you DO have the definite symptoms of a leaking 'O' ring, sorry to say. You could PROBABLY get by with doing the 'block-seal-in-a-can' trick. I had a similar problem and coaxed a good two years out of my engine this way.

I don't see where 25lb's would be that out of the ordinary if you removed the pressure cap on the AST and placed the pressure gauge on there. I would think it would have remained at what ever the cap was rated for, and without the system pulsating i don't see how there could be a seal failure (unless maybe in a portion of the seal that's not under pressure from the inside of the engine)

Any slight cap leakage (a bit of dirt on the seal, etc.), or a drop in engine/coolant temperature could cause this.


Without the AST cap on to relieve the pressure during warmup, I'm not surprised you saw 25 psi (you're lucky you didn't blow out a hose, however). The expanding coolant has to go somewhere to keep the pressure down, and when it can't, the pressure will build up. So, no, that's not a sign you need a rebuild. If you are not now losing coolant, you're probably OK.

Thanks guys for the responses.
jpandes - No bubbles on the "Champagne Test"
bajaman - how did you use the block seal w/o sealing your heater core and radiator?
Dave w- I am seeing some coolant loss

Damn! I guess it is time unless the block weld works!

read my last tread on coolant problem (over flow), i pumped mine up to 25-30 psi.. held over night maybe dropped 5 psi. i had the same problem.. untill i ordered a full coolant hose set. 155.00 14 hose's shipped from mally mazda.. my turbo (2)coolant lines were leaking but burning off on the exh manifold. if your car runs great, and doesnt hold coolant and you know your seals o rings are good.. replace them. you have done everything else.

Same comments as RX7 allnight - make sure you are not leaking externally before you go for a rebuild!

two things - first, what kind of coolant cap did you get? I bought a brand new one from NAPA and it was actually bad. Then spent the ~$15 one from Mazda. You'll find most agree that the mazda cap from the dealer is worth it.

Also, have you checked to see if your pax floor pan is wet (under the carpet) - if so, you would have a heater core leak. Probably not, but you never know... (I had that problem too).