Consequences of Unscrewing Expansion Tank Cap on a Warm, Turned-off Engine

Hello,
what should be the effect of unscrewing the expansion tank cap on a warm engine off?
I hear air sucking in, is it bad?
Greetings,
qer

Rather, you can hear air escaping from the reservoir. You should be able to hear this short psytes and that's it.

qer wrote:

Hello,

I hear air sucking in, is it bad?

qer

You can't immediately write what engine is it, what car etc ....... ???

(fortune teller no longer accepts, they work until 18 )

I do not know 100%, but it is rather not air suction, but pressure released ... that's why there is usually some achtung on the cork ..

It depends on the car, there are cars that have an "open" expansion tank and a closed one (tightness of the plug in the tank because it is not on the radiator), e.g. Audi WV, in these cars there is a similar symptom, but as an overpressure after turning off the engine, but after complete cooling there may be a symptom of negative pressure (due to fluid expansion)

And the check valve in the traffic jam?

Quote:

You can't immediately write what engine is it, what car etc ....... ???

OPEL Astra F 1.6, why am I asking?
Today I was picking up the car from the mechanic, he was showing me what he had done and me
by the way, I checked the oil and coolant levels, they were
ok, but the mechanic said it was after twisting the tank cap
equalizing coolant, you could hear the whistle of the air, it was evidently a sign that I had a gasket under the head and said that occasionally for PLN 500 he would do it to me: / I ignored him, because such a diagnosis only after hearing something, basically without
Checking out other things is probably a failure, but I started now
wondering ... is such a whistle (I do not know if it is sucking or pushing - you can hear the whistle!) on a warm engine something disturbing ??

Normal symptom.

no difference what kind of car it is, the negative pressure in the cooling system hits the leakage of the cooling system-combustion chamber system
very bad indeed, only a book fault

I didn't read until the end,
as there are no problems, do not unscrew

Regardless of what the car is, the negative pressure in the cooling system indicates a leak in the cooling system-combustion chamber system
very sporadically, even only a bookish defect.
Let a friend kindly explain when a vacuum is created in an internal combustion engine? And spelling to be improved.

vacuum is created when fluid is drawn into the combustion chamber,
practically unheard of in passenger cars, in 4-4 layout motorcycles
where the cooler is above the combustion chamber system also not very common, but common
units from the early 1980s
half a year ago, w203 due to such a condition, after replacing the thermostat, it came to me
suction of the vice with the addition of "gas"

WHAT TO WRITE, MR. MODERATOR
WRITTEN ON THE MECHANICS FORUM
If I was looking for help from Polish language teachers, I would write on their forum

qer wrote:

Hello,
what should be the effect of unscrewing the expansion tank cap on a warm engine off?

In the case of some engines (where there is liquid directly under the plug), the effect may be a boiled hand or face. Therefore, I advise you to be careful when playing with the cooling system.

Dawn is due to fluid pressure (air is forced out as warm fluid is). And this is no opportunity to replace PLN 500, the seals costs about PLN 100 (up to 1.7 isuzu PLN 130, so it is probably cheaper for gasoline) and the labor is a maximum of PLN 120.

Oh, I am supposed to understand that the leak is a check valve that allows underpressure, but does not allow a dozen times greater overpressure at the time of ignition?

I have an astra F 1.4 16v, I also had something like that, if it also catches a slightly higher temperature than the standard, the mechanic was right because I had the same thing, you gave the kite too much and the gasket to be replaced

Just to add, the plug closing the cooling system, regardless of whether it is on the radiator or the expansion tank, has two valves: overpressure (something like a safety valve), opening when the pressure increases above a certain value (depending on the performance of the plug) and underpressure, through which it is to occur equalization of pressure in the cooling system (if negative pressure is created in it) with the atmospheric pressure. Both valves should be operational. If the overpressure valve is faulty, i.e. leaky, then the rubber hoses on a hot engine are soft, while if it does not open, the hoses will be as hard as stone. Vacuum valve when it is inoperative: i.e. leaky, symptoms are like a leaky overpressure valve, but when it does not open, the rubber hoses on a cold engine become more or less flat. To check the existence of purges to the cooling system (gas - with gas or exhaust gas - with a blown gasket under the head), I recommend the bottle test (described by me), it is simple, reliable and unambiguous.