One-way radiator caps? Some expansion tank caps, yes. But I've never seen a one-way radiator cap, at least not a modern one.
Does coolant in reservoir ever cycle through the system?
- Thread starter Johnny248
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I like that idea! Usually I do a drain and fill on radiators every few years, but your method (very vehicle specific) sounds easier.
^^^ This.
My Nissan's have these, they did back to at least 2005. It has caused many owners a great deal of confusion - like the fact that the spring cap goes on the degas (overflow) bottle and the solid cap goes on the rad. Also, the rad cap is not the highest point in the system. If you pull the rad cap on a full system even cold, some coolant comes out.
It does make changing the coolant really easy. Fill the rad as much as possible. overfill the degas tank just a little, 1 hot cold cycle then top the tank to the full line. Done.
my old 2009 Sable, there is no "radiator cap", the fill point for the whole system IS the Bottle.
Yup, no cap on the radiator at all, just the tank. First saw this on a '78 Volvo.
A typical overflow expansion tank will push hot coolant out with dissolved air in it and when it cools down suck the now airless liquid back in. If it does not then there is a vacuum leak on cool down. This is easily seen by looking to see that the radiator is 100% full when cold. If it is not then there is some most of leak in the system. Weak OE spring clamps are an issue I have found with time.
If the cap is a pressure cap it is circulated if not then the old fashiond style. My Ford Taurus was the only pressurized coolant tank I had. Other than the tank not lasting and in this case the Dorman was the long lasting go to replacement I prefer that type of system.
They are nice as you never need to worry about air in the system. Usually have a small hose connected to the upper part of the motor and one to the top of the radiator. Air gets vented right there with the pressure cycles.
They are nice as you never need to worry about air in the system. Usually have a small hose connected to the upper part of the motor and one to the top of the radiator. Air gets vented right there with the pressure cycles.
That's not a universal rule either! A Saturn S-series has two hoses. One goes around to the top of the engine and its top radiator hose and is marketed as a "degas" hose. It's higher than "mean high tide" eg the "hot full" line on the pressurized reservoir. I've run these cars with the caps off and anything coming out of that hose is spittle with air.
The other hose is a 5/8" output line that goes to a tee into the heater hose circuit. Sure, coolant put in here will mix eventually. But if someone wants to add "stop leak" and have it work, they need to drain a quart from the radiator. This will put air in the heater circuit and allow new coolant, introduced to the pressurized surge tank, to directly find its way into circulation.
If one were to put Bars Leaks (recommended for these cars) powder in a normally full reservoir it will sit there and turn to sludge with the air present, and do the car little good.
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that sums it up... it depends on the design.
If there is air coming from the degas line, and you don't know where it came from, that's probably a head gasket leak. That is the purpose of it in fact.
Ford has a (very old) video explaining how the "DeGas" cooling system functions
I've had bad luck with non OEM caps
For an overflow style, yes, extremely slowly
In a degas or surge setup, also yes, frequently
I've had bad luck with non OEM caps
For an overflow style, yes, extremely slowly
In a degas or surge setup, also yes, frequently
As I said, IF you don't know where the air is coming from.
