Air suction and exhaust gas leakage in cooling system..

[Fernando Mendes]

Air circulating through the cooling system,as well as exhaust gas leaking into the system,causes rapid corrosion and rust formation which will eventually clog the system and cause overheating and loss of cooling liquid.The air may be drawn into the system due to low liquid level in the radiator,leaky water pump,or loose fitting connections.Exhaust gas may be blown into the cooling system past the cylinder head gasket or through cracks in the cylinder head and block.

AIR SUCTION TEST: Adjust level of cooling liquid in radiator,allowing room for expansion so as to avoid any overflow loss during test.Replace radiator cap with a plain type cap.Be sure cap gasket an airtight seal.Attach a length of rubber tube to lower end of overflow tube(this connection must be airtight).Run engine with transmission in neutral gear at a safe high speed until temperature gage stops rising  and remains stationary.Without changing engine speed,put end of rubber tube in a bottle of water,avoiding kinks and sharp bends that might block flow of air.Watch for bubbles in bottle of water.The continuous appearance of bubbles indicates that air is being sucked into the cooling system.Correct conditions by tightening cylinder head bolts,water pump mounting bolts,hose clamps and fitting connections.Also examine all hose carefully and if cracked,swollen or deteriorated in any way,replace with a new part.

EXHAUST GAS LEAKAGE TEST: Start test with engine cold.Remove drive belt to prevent pump operation.Drain cooling system until cooling liquid level is at top of thermostat housing,but no lower.This can be determined by loosening up cylinder head outlet from thermostat housing to check level of liquid.If liquid leaks from this connection,continue to drain system until liquid no longer leaks.Remove thermostat.Make sure thermostat housing is full of liquid(add if necessary),then with transmission in neutral gear start engine and accelerate it several times.Watch for bubbles in water in thermostat housing while accelerating engine,also when engine speed drops back to normal.The appearance of bubbles or a sudden rise of cooling liquid indicates exhaust gas leakage into cooling system.Make test quickly before boiling starts as steam bubbles will give misleading results.If exhaust gas leakage is evident replace cylinder head gasket,then test again.If leaks are still evident,it indicates cylinder head or block is cracked.Report to  higher authority.Install thermostat,install and adjust drive belt,then fill radiator.