Overfilled coolant




When the expansion tank has no room, extreme pressure gets placed on the closed circuit weak points: head-gaskets, O-rings, hoses, pump seal...
Get your coolant level below MAX soon.
You know the pressure caps are also pressure relief caps, right? The worst that will happen with an overfilled system is some fluid getting burped onto the ground. Not altogether ideal, given it is toxic to things with heartbeats, but I'd hardly lose any sleep over it.
That said, it is easy to pull out a couple of cups of coolant to correct the overfill.








I am not convinced these engines are immune to high pressure damages... one example is the engine oil heat exchanger busting its seal.
Last edited by CaliBenzDriver; Apr 21, 2022 at 03:59 AM.
You know the pressure caps are also pressure relief caps, right? The worst that will happen with an overfilled system is some fluid getting burped onto the ground. Not altogether ideal, given it is toxic to things with heartbeats, but I'd hardly lose any sleep over it.
That said, it is easy to pull out a couple of cups of coolant to correct the overfill.
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Worse can happen is when you top it off on cold engine, the bubble might become too small.
I always top off coolant on warm engine and that makes perfect level.




Air is compressible, liquid is not. Yes, it has the pressure cap but that is a 1.4BAR rating or 20 psi.
50/50 coolant has expansion of approx 6% and commonly expansion tank is 12% of coolant capacity.
Our reservoir is approx 1ish liter and the air space when properly filled ( HALF ) is about 0.5 to 0.6 liters, which correspond to half of 12% of 9-10 liters of coolant.
Our coolant circulation pump or the cooling system overall pressure even at 108C / 226F temperature is only 11 or so PSI at 4,200RPM. Probably at WOT redline it may do 13 PSI at best.
So by having air space for coolant expansion, we have some buffer for pressure increase on the compressible air-space and that is good for plastics.
If all liquid due to an overfilled condition..... sure the pressure cap will allow release but that is pressure torture at 20 psi... pity the cooling system.

Source : https://www.dewitts.com/blogs/news/1...g-should-i-use




pressure to temp relationship
When the plastic cap starts leaking pressure, the boil over temp drops towards 226°F.
Last edited by CaliBenzDriver; Oct 22, 2022 at 02:52 PM.
IT is a relief valve for coolant system.
Reason for air space in bottle is to keep it from over-flowing as fluid expands when heated and keeping garage floor nice and clean.
IF it leaked out excess on to floor, owners would be bringing cars back in all the time for warranty;
so fix was external tank with Hot Min/Max lines halfway up.
Before this all they had was cap on radiator and drain hose down the side to near ground - Think 70's
When it dumps air = no mess.
When it dumps over-filled coolant = mess out of that hose which snakes to near ground near cap.
Just wait for it to cool and get OLD turkey baster and take some out.


