Purpose of Coolant Tank - Pressurized Version

[DBMaster]

I apologize to those of you who already know this, but I just learned today that the pressurized plastic coolant tank on my 2012 Mazda3 serves primarily to keep air out of the cooling system. It is mounted higher than the rest of the system. It has a relatively low pressure cap that allows air out when it exceeds a certain pressure and lets air in when the vacuum exceeds a certain pressure. I have posted a photo below. The two small barbs are inlets. One is an engine return line connected to the thermostat housing and the other is a radiator return line. The lower, larger barb returns coolant to the radiator. It is internally baffled to "burp" air from the system. I was ignorant before and now feel educated.

 

[eljefino]

It should also slow down the evaporation of the coolant inside.

A nonpressurized tank will have quite warm coolant enter via the overflow hose. It's natural that it would want to evaporate. A pressurized cap will lessen that.

 

[abycat]

Yeah I have the same thing on my diesel. It's very important on it. my car has the normal type.

 

[DBMaster]

I did notice that when Mazda redesigned the Mazda3 for 2014 they went with a non-pressurized tank. I am thinking that mine may have still had some of the Ford influence? I have the Skyactiv version.

 

[DBMaster]

Originally Posted By: eljefino
It should also slow down the evaporation of the coolant inside.

A nonpressurized tank will have quite warm coolant enter via the overflow hose. It's natural that it would want to evaporate. A pressurized cap will lessen that.


Very good point. I have added 4 oz of RMI-25 every 15K miles since learning about it on this forum. The coolant level remains constant after 67K miles. I guess that means a very small amount of evaporation is going on, but not much. This type of tank allows for constant exchange of fluid within so it doesn't get gross and dark.

 

[simple_gifts]

I believe my B2300 (ranger) has this. Coolant is constantly pumped thru it, and D+F are done adding coolant to this tank.

 

[Chris142]

That's how gm fixed the dexcool problem

 

[tmorris1]

That is how Ford systems are as well. That cap is essentially your radiator cap

 

[DBMaster]

I recall my dad's 1984 Renault Encore had one. The radiator also had a cap. On my Mazda there is no cap for the radiator at all. It's entirely closed with a couple extra hoses connected to this tank. I actually think I like this design better than the other. Though, catching crud from the cooling system in the other type of tank allows you to simply empty and refill it to remove it from the cooling system.

 

[SumpChump]

Not sure why .... But i just dont dig pressurized tanks.

 

[CapitalTruck]

I thought almost all cooling systems were put together this way now. Of course, I tend to only buy GM cars so I guess I'm not exposed to a lot of the market.

 

[CT8]

My moms 59 thunder bird had a pressurized thank and my wife's 2002 ford F250 with the Powerstroke and my 2015 Ford F150 has one. Good or Bad I don't know.

 

[DoubleWasp]

The real shame is that not enough manufacturers use them to their full potential. The best part about these tanks is that they can be fed from strategic points in the cooling system where air and steam is known to collect.

Yet, there are many cooling systems with pressurized tanks that will air lock like a mother.

I have seen some (particularly Fords) that make good use of them, with 2 or more connections to the tank coming from strategic points.

 

[SteveSRT8]

Originally Posted By: Chris142
That's how gm fixed the dexcool problem


Then please explain how our 3500 vans with an open tank do not have dex issues...

 

[dlundblad]

I had to replace the PNP switch in her Volvo on Saturday.

While checking out everything else, I noticed her pressurized tank had some dried coolant built up on the side and that it was leaking. I wonder if the pressure tank relieving excess pressure is what saved it from popping apart?

I wiped it with isopropyl alcohol and temporarily patched it with a 2 part epoxy and went ahead and ordered $15 part from RA.

 

[SteveSRT8]

^^^Sure hope you replaced her cap!

 

[DBMaster]

Originally Posted By: SteveSRT8
Originally Posted By: Chris142
That's how gm fixed the dexcool problem


Then please explain how our 3500 vans with an open tank do not have dex issues...


Heck, I had an 89 Accord that I owned from 1989-2012. In 1997 I learned about this new-fangled 150,000 mile coolant called DexCool. I did a simple purified water flush and put Dex into the Accord. I drove the car another fifteen years and 200,000 miles without ever changing the coolant again. I should note that I did replace portion of it when replacing the water pump (part of timing belt job) and a few coolant hoses in 2009. I never did figure out what all the DexCool dread was about.

 

[Yah-Tah-Hey]

I can't see how this is very much different than the current overflow tank set up vented to atmosphere.You will still have ambient air pressure pushing coolant back into the radiator.No matter what the arrangement,cooling systems are open to ambient.

 

[DBMaster]

Originally Posted By: HosteenJorje
I can't see how this is very much different than the current overflow tank set up vented to atmosphere.You will still have ambient air pressure pushing coolant back into the radiator.No matter what the arrangement,cooling systems are open to ambient.


This type of tank is under pressure. The overflow tank is not. This tank also should eliminate the need to bleed air from the cooling system when servicing. It is also generally mounted higher than the rest of the cooling system rather than lower like the overflow tank.

The differences are not HUGE, but they are significant. Try opening this one to add coolant when the engine is hot...

 

[bugeye]

The P2 Volvo cars are reported to have leakage issues with the coolant expansion tank. Replace only with Volvo part as aftermarket parts are reported to fail in shorter time.