Coolant Overflow Container Gasket Thingamerbop.

A recent coolant leak (fixed this weekend) allowed me to learn that the coolant system was not pressurized. As the level of coolant in the radiator decreased it did not suck more coolant out of the reservoir.

To remedy I'll start by getting a new radiator cap. On top of that I believe the gasket in the snap on plastic top of the reservoir might be letting air in. I'd like to replace that as well.

Can someone point me in the right direction of finding out exactly what that gasket is and where I might get one as cheaply as possible? Any additional guesses at what the problem might be would be appreciated as well.

Thanks.

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Originally Posted by Bell

A recent coolant leak (fixed this weekend) allowed me to learn that the coolant system was not pressurized. As the level of coolant in the radiator decreased it did not suck more coolant out of the reservoir.

To remedy I'll start by getting a new radiator cap. On top of that I believe the gasket in the snap on plastic top of the reservoir might be letting air in. I'd like to replace that as well.

Can someone point me in the right direction of finding out exactly what that gasket is and where I might get one as cheaply as possible? Any additional guesses at what the problem might be would be appreciated as well.

Thanks.

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Bell the overflow bottle has a hole in it already to allow the bottle to overflow, and isn't pressurized. Not sure I understand what you need??

Didn't the Radiator cap cure your problem?? This problem sounds familiar.

You could have a leaky hose these little cars have quite a few hoses :http://www.mazdamotorsports.com/wcsc...0_93mcool.html

Well here is my understanding of it. Tell me if I'm wrong.

As the coolant in the radiator gets hot it expands and the excess goes into the overflow reservoir. Then as it cools it sucks coolant back into the radiator because of the change in pressure.

This is not happening. I assume it is not because the reservoir is leaking air somewhere. I believe it might be the gasket in the plastic cap or at least this would be a cheap place to start.

Any thoughts?

You are correct about this being related to the previous problem. My temperature gauge was fluctuating because I had a coolant leak. I checked the reservoir and that was full so I assumed I had plenty of coolant. Turns out when I took off the radiator cap there was no coolant to be seen.

I finally fixed the coolant leak this weekend. The problem stemmed from me previously changing the timing belt and water pump. Two important lessons learned. They're pretty technical so you might want to write them down.

1. Tighten ALL the bolts connecting the water pump to the engine. Three out of four is not quite good enough.

2. The paper gasket belongs between the water pump and the engine block. It should not be left in the box.

Yes, I am new at this.

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You have a pressurized system...

The pressurization stops at the radiator cap... not at the coolant bottle.

The overflow tank is to catch whatever shoots out from the cap due to too much pressure... If you have no pressure then you have a leak... at the cap or somewhere else in the system. Same goes for coolant getting sucked back in... won't happen if the system isn't pressurized properly.

It could be either a hose or clamp... bad gasket somewhere... or a bad O-ring.

Could also be a (gasp!) water pump.

My 92 blue had a leak at the water pump shaft... my 92 B&T had a leak from the O-ring behind the water pump.

Others here have had leaks from the heater hoses going to the firewall due to a leaky CAS O-ring dumping oil on them and weakening them.

Basically if your system isn't pressurizing properly then the coolant won't go from the overflow tank into the system... and the overflow reservoir is not part of the pressurized system.

Raymond

Quote:

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Originally Posted by Bell

Well here is my understanding of it. Tell me if I'm wrong.

As the coolant in the radiator gets hot it expands and the excess goes into the overflow reservoir. Then as it cools it sucks coolant back into the radiator because of the change in pressure.

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Run out and look at the overflow bottle, there is a neck on it that allows for coolant to flow out of the reservoir bottle if it is too full. So it is not a pressured unit. The radiator on the other hand is and when pressure exceeds the system pressure it allows coolant to overflow into the overflow tank, when everything cools off and the radiator pressure drops it will pull back the coolant out of the overflow.

Take a peek at this: http://auto.howstuffworks.com/cooling-system1.htm

This is the overflow bottle on a 2002 Miata (with ABS) note the overflow built into the bottle.
http://www.harrisonindustrial.com/im...Overflow02.JPG
This is the overflow bottle on a 1992 Miata note the overflow built into the cap.
http://www.harrisonindustrial.com/im...verflow92a.JPG
http://www.harrisonindustrial.com/im...verflow92b.JPG

Okay let me run this past you. In that article it says...

"When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled."

Obiously when the there was a coolant leak, even though coolant was coming out at the waterpump, that did not create enough pressure to pull coolant in from the overflow. I just assumed if it leaked out one place it would suck it in from the overflow. Guess not.

So therefore, if everything is working smoothly when I fill the radiator all the way to the top, it should always stay filled to the top. There might not be anything wrong with it at all. I'll have to go check.

Sound about right?

Sounds good to me!

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When the fluid in the cooling system heats up, it expands, causing the pressure to build up. The cap is the only place where this pressure can escape, so the setting of the spring on the cap determines the maximum pressure in the cooling system. When the pressure reaches 15 psi, the pressure pushes the valve open, allowing coolant to escape from the cooling system. This coolant flows through the overflow tube into the bottom of the overflow tank. This arrangement keeps air out of the system. When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled.

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Keep in mind this only works when you have a system that will pressurize, if it doesn't pressurize all bets are off, like when you have a leaky water pump or hose.

Thanks for the help.

Good luck!

If you can't find the leak you can try putting a pressure tester on it and putting dye in the coolant...

Then you can use a blacklight to find where the leak is.

Raymond

Wow as good as you are at that, you could be a Barkers Beauty. Oh and also, he is right, it is the radiator cap that holds the pressure in, once the pressure exceeds that it lets fluid into the overflow.

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Originally Posted by POS Racing

This is the overflow bottle on a 2002 Miata (with ABS) note the overflow built into the bottle.
http://www.harrisonindustrial.com/im...Overflow02.JPG
This is the overflow bottle on a 1992 Miata note the overflow built into the cap.
http://www.harrisonindustrial.com/im...verflow92a.JPG
http://www.harrisonindustrial.com/im...verflow92b.JPG

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