What causes high pressure in cooling system? - 1993 Chevrolet Suburban

I can give you a general answer. the cooling sys is a closed system. as the engine warms up pressure is also increased. kinda like how a boiler works, or a pressure cooker. i dont know the figure of how much pressure is produced within an engine that is operating normally. the engine's thermostat. the thermostat of many car engines opens at 195 deg coolant temp, allowing the coolant to circulate. high pressure when considering a car's cooling sys to me is relative. if you try to remove the radiator cap when the engine is at/near/above operating temp you will be burned by the hot coolant under pressure rapidly escaping out the radiator. most pressure that is above normal is caused by an obstruction somewhere in the system. a t'stat that is stuck shut is an example. air pockets within the system will also lead to high pressure within the system. air pockets occur when you refill the system with coolant/water. pouring water/coolant back into the radiator traps air that can circulate throughout the system and you must ensure that these air pockets escape out the radiator, or you risk damaging the engine from excessive heating.

I am assuming that you really mean the radiator cap is boiling over, because it acts as a relief valve.
The main reason the radiator cap blows is because there is not enough coolant, so it turns to steam and has higher pressure.
But you could also have a stuck thermostat, bad water pump, or bad head gasket that lets engine compression get into the cooling system. Fill the system and try a new cap. Make sure there is a recovery over flow container, or you don't over fill also, because it needs room for expansion when it gets hot.

Most cooling systems require pressure in the cooling system. That is what the radaitor cap does. It releases pressure to the overflow tank when there is to much pressure and it also has a second valve to put fluid back in when there isn't enough pressure or a vacumn. But I think about the highest pressure I have every seen stamped on a radiator cap is 15 psi.
I don't know how much pressure your vehicle is putting out. I believe when your car is warmed up you should be able to squeeze the top hose but with effort.
If you can't, I bet most auto repair shop have a pressure tester. It could be as simple as a faulty radiator cap or bad thermostat. the worst case would be a bad head gasket(which you would want to fix promptly as this could ruin your engine in minutes if it is bad enough).

Hope this helps

Hi Charles,

Two factors affect the boiling point of water. Heat and pressure. The higher the pressure, the more heat it takes to boil. The lower the pressure, less heat.

The heat generated by your engine is transferred by the water in the cooling system to the radiator where it dissipates. Once cooled it is cycled back through to do it again. Heat up, cool down.

The cooling system is what is called 'closed loop'. What's inside stays inside. Also, only a portion of the water is getting cooled at any given moment. The rest is heating. As the temp reaches boiling steam starts to be produced which increases the pressure inside the system. With that increased pressure the water doesn't boil any more. It keeps transferring heat to the radiator.

If that pressure is suddenly decreased (like the radiator cap being released) the heated water will spontaneously start boiling violently.

This is why filler caps have a two stage twist for removal. The first releases the pressure without letting the cap loose. The second releases the cap. This safety feature has saved countless people from an eruption of scalding water.

I hope this answered your question.

Best regards,
Mike

Should have normaly about 15 psi for the system but if it is blowing out coolant it could be just over heating. If you have never flushed the cooling system out. Take it to a raderator shop and let them do it. The DYI stuff only works for every year maint. Look forward to a new raderator. Hope this helps

First thing I would try is remove your radiator or degas bottle cap you have a degas bottle cap if your radiator does not have a cap it self, fill radiator with distilled water all the way to top of the cap, do not put the cap on just yet, start your engine and watch the radiator or degas bottle *Caution do not put your face directly over the cap opening, allow engine to run for a few minutes like this, look for large percolating bubbles as the engine warms up usually in 2-3 minutes, if the bubbles are causing the coolant to over flow very rapidly but is cool to the touch and there is white smoke or steam coming from your tail pipe chances are very good you have a blown head gasket , cracked or warped head, the engine is pushing cylinder gasses back into your cooling system thus over pressurizing it via a faulty seal at the head... lots of luck or they can check your system for these gasses at a repair shop...good luck

Wrong water pump,,,possible,,,could be blown head gasket,,,or timing to low will cause it to run hot

Several things can cause over heating, Cracked head , blown head gasket , faulty thermostat, blocked radiator core , faulty radiator cap, radiator cooling fins blocked with rubbish, mechanical fan loose belt or slipping fan clutch, electric fan not engaging both engine and air con fans, auto transmission oil to hot and heating radiator coolant. Take to radiator repair shop if you don't have the tools to check the above.