So in preparation for my sniper install. I pulled the thermo vacuum switch. on the driver side front of the intake. To put in the Sniper temp sensor. The coolant came out like a geyser. I haven't started the car in at least 2 days. Popped the Radiator cap nothing just coolant. What would keep pressure in the cooling system. Bad thermostat? Maybe that was my issue when I drove to Lincoln in May. Thanks Tim
I wouldn't think the thermostat would pressurize it much since the pressure behind the thermostat can equalize through the heads to the block and back through the water pump. In a closed system, they get hot, push fluid into the overflow once they exceed the cap pressure. When they cool, they pull most of it back. The pressure in the system likely is just the difference between the coolest it has been and the temp on the day you loosened it. My gas cans swell up on a warm days and one will nearly collapse on a cold day if they aren't almost full.
A properly operating coolant system with a 14-16 lb. cap, can maintain system pressure for several days. Not likely a problem, and you are not the first person to be surprised.
Never try to work on the cooling system without draining the radiator to below the component you are working on, intake fitting, thermostat housing, etc. The level of the coolant in the radiator is higher than the intake manifold. Gravity caused your coolant spill.When the coolant level in the radiator fell to the level of the intake, the spill ceased. In the future, if you want to avoid that, drain the radiator enough to lower the level to below the intake before taking anything apart. Pressure in the system dissipates as the coolant cools and contracts, sucking coolant back in from the recovery tank. As coolant heats up and expands, it creates pressure in the system which the radiator cap limits to 15 psi. or whatever it is rated to.
Boy you guys are something else in your line of thinking let me tell ya!! If your cooling system still has pressure in it after hours of sitting a room temp then you have a problem! That being one or more of your cylinders due to many possibly reasons is pumping up the cooling system, period! if you do not believe me then borrow someone’s pressure cooker, get it up to the point of making pressure and then let it cool down over night, the next morning you will find zip for pressure in it! In fact if you have lost some coolant from the level you started at and then allowed the system to cool back down you will not find pressure in the system if you open a lever type rad cap, but you will hear a vacuum condition being filled up by Atmospheric pressure.
A pressure cooker is far from a sealed system like a radiator cooling system is but like a car radiator, it is designed to limit high pressure and offers little resistance to low pressure. If it cooled overnight, it could pull more in from the overflow tank. If it changed 30° between 5AM and 2PM, which is quite common this time of year here in Kentucky, it could have ambient pressure. Any air in the system would cause greater pressure due to gas expanding against the liquid.
Your assessment is completely wrong. 3 factor's make the pressure rise seen in a sealed system. These 3 factors assume that you have burped the cooling system from air when the T stat first opens . This is a nessity in any cooling system where the radiator cap sits above the highest coolant level in the motor. Three factors. 1) water pump pressure. 2) expanded fluid volume due to heat. 3) added pressure made by bioling of coolant or water out of the coolant mix in localized hot spots in the cylinder heads. When you take away all three of these as when everything that comprises the cooling system is back down to the ambient it was at when it was first filled then there will be no pressure in the system. If pressure could be maintained for days on end with no physical or thermal input to the system then you have miraculously found a source of free energy and you can make a fortune!
You guys are getting off the beaten path here. This has nothing to do with retained pressure. Pulling a thermo vacuum switch out of the intake without first draining the radiator down to that level is a foreseeable mistake. The resulting geyser of coolant is to be expected. The intake manifold is lower than the top of the radiator. Think of a U shaped tube. Add water to the tube, and the level will equalize on both sides of the tube. Then take a plunger, and insert it into the tube on one side. Push down the plunger until the water level is even with edge of the other side of the tube. What happens when you suddenly pull the plunger out? The levels quickly equalize again. Think of the thermo vacuum switch as the plunger, and the other end of the tube as the radiator water level. Pull the vacuum switch out, and the levels equalize with a spill. Lots of guys will use this method as a way to ensure no air pockets in the system. They will pull the thermo vacuum switch or coolant sensor out of the intake. Then, they fill through the radiator until coolant seeps out of the sender hole. Put the switch sender back into the intake, fill the radiator, and start the engine. Leave the cap off, and keep the radiator full as the stat opens up. Put the cap back on, and you are done.
