Coolant Recovery System
Page created by T Aug 10th 2007:
 Coolant Recovery System:
 Pressure and Temperature are Related:Boyle's Law states that Pressure, Volume and Temperature are related. A high Temperature means a high Pressure inside the Cooling System because the Volume remains the same. A low Temperature means a low Pressure inside the Cooling System also because the volume remains the same.
When a car is cooled by a Radiator the Radiator has to have provision for expansion when the engine heats up and provision for contraction when the Engine cools down.
 Expansion:Holdens have had a pressurised Radiator Cap from FX on. The Radiator Cap keeps the coolant under pressure when the Engine is hot. Being under pressure raises the boiling point of the Coolant and prevents the Coolant from being boiled away.
The pressure is kept from becoming excessive by the spring tension above the rubber valve in the Radiator Cap which allows the releasing of Coolant out of the overflow pipe when the pressure exceeded the pressure stamped on the Cap. This keeps the cooling system from blowing hoses.
When the Engine is at normal operating temperature the Radiator is full.
A disadvantage of the system is that every time the engine gets hotter than average some extra Coolant is lost out of the Overflow Pipe
which drips onto the road.
When the Engine is cooler than average an airspace exists at the top of the Radiator which reduces the efficiency of the Radiator.
 Contraction:When the engine stops and the cooling system cools down, the Radiator Pressure falls due to the lower temperature surrounding the Car.
At this point the Coolant itself contracts and creates a vacuum. The vacuum draws air back into the Radiator.
Another disadvantage of the system is that when the Engine is cold an air space is left in the top of the Radiator between the coolant and the Radiator Top Tank. The air space was responsible for permitting the presence of deposits within the Radiator.
In the centre of the Radiator Cap there is a smaller valve which allows Air to flow back into the Radiator when the Engine cools down.
 Overflow Bottle:Later model Holdens came with a Coolant Recovery System. Without the Recovery Bottle the Radiator needed periodic topping up with Coolant to replace that which was lost when the Engine temperature exceeded the average. The Coolant Recovery System means that Coolant rarely needs to be added. When it does it usually means there is a problem with the Cooling System.
The Coolant Recovery System uses a special Radiator Cap which ensures that Coolant can only flow into the Recovery Bottle when the Radiator Pressure is high enough and can only flow back into the Radiator when the pressure is low enough.
The cap also ensures that no Coolant can spill out onto the ground by having an extra seal in the top.
The Coolant Recovery System keeps the Radiator full at all times reducing the buildup of scale by ensuring there is no airspace in the top tank.
A pipe is connected from the Radiator Overflow pipe to an Overflow Bottle. It's important that the Overflow Bottle be placed close the to Radiator and close to the level of the top of the Radiator. This is important, because when the Engine is cold the recovery vacuum can stress the Radiator and Hoses. When the Overflow Bottle is at the appropriate level the recovery vacuum is kept to a minumum and the Cooling system is less stressed.
The Overflow Bottle must have provision for expansion so a pinhole must be present.
 Fitting a Coolant Recovery System:This is easy to do. The Coolant Recovery Bottle can be bought cheaply and should be mounted in the recommended location and connected to the Radiator OverFlow pipe by a Rubber Hose. A Coolant Recovery Radiator Cap must also be used.
 Coolant Level in the Recovery Bottle:Sometimes the Coolant Level is marked on the OverFlow Bottle stated as a minimum level for when the Engine is cold and a maximum level for when the Engine is hot. Overfilling the Bottle will result in Coolant being spilled into the Engine bay when the Engine is hot. Underfilling the Bottle will result in air being drawn into the Radiator when the Engine is cold. Often the first discharge from the Radiator Cap can be intense so the extra space in the Overflow Bottle can allow for the burst of Coolant that will be thrown into it as well as condensing any steam and converting it back to coolant.
 Winter and Summer:During Winter the Engine will cool more when shut down. This will mean more Coolant will be drawn into the Engine. Checking the Coolant Level in the Overflow Bottle will show that the level has gone down further than in Summer.
During Summer the Engine will not cool down as much as in Winter so the Coolant level in the Overflow Bottle will not be as low when the Engine is cold.
 Contaminants:Contaminants such as rust and crystalised Coolant can collect in the Recovery Bottle. When the Engine cools down these can be drawn back into the Cooling System. They can lodge under the Return Valve in the Radiator Cap, prevent it from sealing and holding pressure.
Periodically the Radiator Cap will need to be removed and be cleaned in addition to replacement when the rubber seals wear out.
Periodic flushing of the Recovery Bottle may become necessary if an excessive amount of contaminant collects in there.
Crystalised Coolant will likely dissolve back into solution again if drawn back into the Radiator.
 Coolant Recovery Bottle - Low Level:If the level in the Coolant Recovery Bottle goes right down or it is empty it means that the Radiator has a leak somewhere. Even a pin leak will cause the level to go down. To fix, check that the Radiator Cap is clean and that the rubber seals are in good condition. If in doubt replace the Radiator Cap with a new Recovery type one. Next tighten all the hose clamps. Check for signs of Coolant leaking from anywhere. Check that the Waterpump Seal is intact. Giveaway signs are Coolant trails on the Fan Belt Pulleys and/or Belt or on the Harmonic Balancer. Sometimes a Dental Mirror is invaluable for viewing the leak hole drilled into the underside of the Waterpump. A dentist's mirror is about the only way you can see it short of taking the Waterpump off the Engine.
 Coolant Recovery Bottle - High Level:This occurs when the engine is hot and can be caused if the radiator cap is not holding pressure. Contaminant in the centre valve is a likely cause. Clean out the centre valve with a clean rag, purge all the air out of the radiator by hand priming, then refit the radiator cap When full of coolant, it must not be possible to squeeze the top hose flat, even when the engine is cold. A leaking radiator cap will allow the hose to squash fully flat meaning that the system will not hold pressure.
 Hand Priming:This a way of filling the radiator right to the top. With the radiator cap removed, seal the hole by covering it with the palm of one hand, then squeeze the top hose hard and flat. You will see coolant and any air appear in the recovery bottle. Keep the palm of your hand in place and release the hose, coolant will be drawn back into the radiator. Top up the recovery bottle if the level goes down then repeat this process until the radiator is completely full.
 Checking The Recovery System Works - Engine Cold:With the radiator cap removed, seal the top of the radiator with one hand and squeeze the top hose. You will see coolant and any air appear in the recovery bottle. When you release the hose, coolant will be drawn back into the radiator.
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