Two catch tanks
- Thread starter bune
- Start date
These are normally part of the coolant system. One of the two tanks is almost always a surge, or expansion tank and has a pressure relief cap, usually 12-16 lbs/in2 This allows the engine coolant fluid to expand as it heats. If the volume when hot exceeds the capacity of the tank, the cap opens as the rated pressure is reached and dumps, or transfers, fluid to the other tank which is a catch, or overflow tank. This tank has a non-pressurized cap or some sort of vent to outside air. When the engine cools down, the coolant contracts and the "excess" fluid that was dumped into the catch tank is sucked back into the surge tank and system. The "in" port to the catch tank is at the bottom of the tank so it is covered by fluid, allowing suction to pull the fluid back. The surge or expansion tank has it's overflow port positioned outside , or after, the pressure cap so it feeds to the catch tank only when it is full and the pressure has exceeded the cap rating. Check the photos. Right side (viewed from rear facing forward) is the expansion tank, left side is the overflow.
Other uses for tanks mounted thusly are for transaxle oil reservoirs or swirl pots for engines using fuel injection but these applications will be mounted much lower in the chassis.
Any vaporized oil from the engine is caught by the baffles in the oil breather caps, usually mounted on the rocker arm covers. It drains back into the cover. If your engine was pumping out so much oil vapor that you needed at least a quart or liter size tank to catch it, you would have a SERIOUS blow-by problem. Some engines will use a PCV valve connected to the rocker cover to recycle that vapor into the intake system, usually at the base of the carburetor.
Other uses for tanks mounted thusly are for transaxle oil reservoirs or swirl pots for engines using fuel injection but these applications will be mounted much lower in the chassis.
Any vaporized oil from the engine is caught by the baffles in the oil breather caps, usually mounted on the rocker arm covers. It drains back into the cover. If your engine was pumping out so much oil vapor that you needed at least a quart or liter size tank to catch it, you would have a SERIOUS blow-by problem. Some engines will use a PCV valve connected to the rocker cover to recycle that vapor into the intake system, usually at the base of the carburetor.
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Rune
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Thanks for the answer, but when looking on pictures from original cars there are already one tank for the coolant + the two tanks high up on wall on each side. So there must be some other function for at least one of the tanks . And these tanks have no cap so I assume that they are a kind of catch tanks , one for oil and one for coolant fluid.
Rune
Rune
