Avoid Opening DEX-COOL Surge Tank?

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Jun 6, 2020
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To prevent gunk formation and other problems, a DEX-COOL system should remain filled with the appropriate amount of DEX-COOL, rather than excess air. However, some have expressed concerns about opening the system:
I dont want to keep opening the radiator or resivoir to check and be letting air into the system!
i don't remove my rad cap for nothing [and let air in]
Consider a leak-free system in which the DEX-COOL is about an inch below "full cold," but at least an inch above above the surge tank's coolant inlet. Should the system be topped off, or is it best to avoid opening the cap?
 
A cooling system surge tank should be filled to the “HOT” line, when the car is cold...
And why is that? Isn't the recommendation to fill the surge tank to the "cold" line when the car is cold? The coolant then rises to the "hot" line when the engine warms up, no?

Any reason to avoid opening the system, as recommended in the quotations I posted?
 
Please note that I'm not asking about the ideal coolant level. The coolant is indeed slightly lower than recommended, but I'm wondering if it's best just to leave it, so as to avoid opening the system.
 
Doesn't make any sense to me.
Some articles from the mid 2000's claim : " To avoid sludge problems, the cooling system must be kept full. GM advises filling the reservoir bottle to the HOT level when the system is cold. Keeping air out of the system is the key to preventing problems down the road." https://www.underhoodservice.com/under-pressure/

The idea is have as little air as possible in the system. I never heard not to top off your coolant level. Looking forward to someone posting facts.
 
The surge tank should be the highest point in the cooling system. The "system" you want to avoid getting air into starts at the coolant level, so opening the cap isn't going to make any difference.

There's no harm in filling your tank to the Full Cold line, if that's what you're asking.
 
To prevent gunk formation and other problems, a DEX-COOL system should remain filled with the appropriate amount of DEX-COOL, rather than excess air. However, some have expressed concerns about opening the system:

There's nothing special or unique about Dex-cool that makes it allergic to some extra air in the surge tank. That's another Dex-cool myth that has it's origins in the early days of Dex-cool when GM had QC issues with the caps not holding pressure which lowers the boiling point and increases the chances of overheating. Some vehicles would overheat and dump a bunch of coolant, owners would refill with water which has no corrosion inhibitors and the rust aka gunk issues would start. The leaking caps also allowed coolant to evaporate from the tanks which would lower the coolant level over time and again could causes corrosion issues because of air pockets forming in the system. Any other OAT coolant would have the same issues in those circumstances. If the surge tank is at the min level rather than the max level will make not difference, if you're a quart or two off that's a problem.
 
Slightly off topic but My 2010 Frontier and others of the same generation when cold and filled only to the cold line, will not provide heat at idle. I joined the Club Frontier forum. The answer was to fill above the line until heat was constant. Worked like a champ!
 
The surge tank should be the highest point in the cooling system. The "system" you want to avoid getting air into starts at the coolant level, so opening the cap isn't going to make any difference.

There's no harm in filling your tank to the Full Cold line, if that's what you're asking.
Yes, I was wondering if there's a compelling reason to avoid opening the cap. I guess the answer is no.

So, is there a compelling reason to top off to the proper level, rather than leave as is?
 
I'm still using DexCool in my 1999 Alero. The LIM gasket that I replaced once looked perfect when I removed it. Now some of the LIM bolts weren't torqued properly from the factory, but for some reason the coolant is blamed.
 
I'm still using DexCool in my 1999 Alero. The LIM gasket that I replaced once looked perfect when I removed it. Now some of the LIM bolts weren't torqued properly from the factory, but for some reason the coolant is blamed.


this creepy video from mahle confirms it was the gasket material
 
Are there any drawbacks to operating the system a quart below the recommended level, as long as the cold coolant level is at least an inch above the surge tank entry hose?
 
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