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Cooling System flush info:

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Old 07-10-05, 11:19 AM
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Cooling System flush info:

In response to a PM I received about changing the coolant:



First off, I'd recommend you read through the entire owner's manual, if you've got it. It will explain simple maintenance things like oil changes, spark plugs, and coolant changes. If you don't have yours, someone has scanned a copy here: http://www.iluvmyrx7.com/1993_new_vehicle_docs.htm



Rob Robinette has a good how-to for the cooling system on his website also.
http://www.robrobinette.com/flush.htm



For future use, it's nice to have a copy of the factory service manual. This is what the Mazda technicians were given to learn how to work on these cars. http://www.iluvmyrx7.com/1994_factor...ice_manual.htm




Here's a photo showing which cap is which, as Robinette's site assumes you already know this:



From left to right: The overflow tank is a reservoir for coolant, its level will change depending on the temperature of the engine. It should be at least half full with water or coolant at all times, because coolant is sometimes sucked back into the system (from this overflow tank) as the car cools. You might need to refill it periodically, because it can evaporate.

The filler neck is where you add coolant and check the coolant level. The cap should not have a spring in it.

The Air Separation Tank should have a 13-16psi pressure cap on it, with a spring mechanism on it.







When flushing the coolant, I recommend using this tool also. After you'v flushed with water and refilled the system with coolant, use this to remove air bubbles. Don't use it with pure water because pure water will boil at 0 pressure (don't ask me how I know...).

Coolant Burping Tool/ Radiator Cap Funnel
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/radiator-cap-funnel-eliminate-air-bubbles-342309/


Good luck,
-s-
Attached Thumbnails Cooling System flush info:-fd3s_cooling_caps.jpg  

Last edited by scotty305; 07-10-05 at 11:29 AM.
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Old 07-11-05, 10:04 AM
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Very helpful summary.

The engine has a "secret" coolant drain plug that is not mentioned in the FSM - it is on the driver's side. See Rob Robinette's site for a picture of the drain location.

Also, the pressure cap on the AST was originally 1.2 atmospheres (about 18psi) and was changed to 0.9 (about 13psi) as part of the factory recall - they lowered the system pressure (and upgraded some components, depending on production date) because some of the original hoses couldn't take the combination of heat and pressure, with the result being engine fires.
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Old 07-27-05, 12:47 PM
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Why should the filler neck have a cap with no spring? Is it OK to run one with a spring on it?
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Old 07-27-05, 12:55 PM
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You might also want to mention unplugging the throttle body coolant hose when you fill up the coolant to limit air bubbles.
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Old 07-27-05, 01:02 PM
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Originally Posted by oneflytrini
Why should the filler neck have a cap with no spring? Is it OK to run one with a spring on it?

The cap with the spring allows coolant to enter the space between the sprung seal and the sealed top of the cap after the set pressure (0.9 or 1.2 bar) is exceeded. The AST has a hose nipple in this area for this coolant to flow to and from the overflow tank. The filler neck has no overflow port between the sprung seal and the cap top, so the coolant goes nowhere. While it shouldn't hurt to have a relief-type cap at the filler, it would perform no useful function, unless the AST has been eliminated and a filler neck with a nipple in this area (to the overflow tank) has been substituted.

Last edited by DaveW; 07-27-05 at 01:07 PM.
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Old 07-27-05, 01:22 PM
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Originally Posted by DaveW
The cap with the spring allows coolant to enter the space between the sprung seal and the sealed top of the cap after the set pressure (0.9 or 1.2 bar) is exceeded. The AST has a hose nipple in this area for this coolant to flow to and from the overflow tank. The filler neck has no overflow port between the sprung seal and the cap top, so the coolant goes nowhere. While it shouldn't hurt to have a relief-type cap at the filler, it would perform no useful function, unless the AST has been eliminated and a filler neck with a nipple in this area (to the overflow tank) has been substituted.
So basically a cap used with a spring, on the filler neck would be no different than a cap without a spring. Unless the coolant has somewhere to vent or "purge"?
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Old 07-27-05, 01:43 PM
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^^^^^

Yes.
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Old 07-27-05, 03:27 PM
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^ Thanks, Im flushing the coolant from the car and was replacing the caps. I bought a Greddy (13lbs) cap, and it had a spring. I got worried when I saw this thread...
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