Join Date: Dec 1999
Location: Cincinnati Ohio,USA
Your engine will overheat for a few reasons:
1. Lack of coolant. This is created by a leak and the symptoms are typically the same each time it overheats. You fill up the radiator, everything is OK for awhile (20 miles maybe) then it overheats. It overheats because the leak creates a shortage of water or coolant.
The repair is to simply pressure test the cooling system and find and fix the leak. We have hand held pumps which we attached to the neck of the radiator after we remove the radiator cap. We look at the pressure limit of the cap. It might say 13 psi. We then pump air into the radiator and cooling system until the gauge reads 13+ psi. The newer the system, the higher over the cap pressure you can go. Likewise, if you have a 15 year old cooling system, you better not pump the system to 20 psi with a 12 pound cap or you will pop it like a balloon. This cooling system pressure test is typically $25-40 dollars.
2. Lack of circulation. This is caused by a closed thermostat, a plugged radiator or a bad waterpump belt or a bad waterpump.
If the engine seems to overheat more around town and seems to be fine on the highway, that is a clear indication that the air flow across the radiator has been effected. This typically means a bad fan clutch or a bad electric fan or relay or the sensor that is supposed to trigger the fan relay that turns the fan on.
If the engine seems to be fine while driven slowly (35-45 mph) and overheats quickly on the highway (55+) and takes forever to cool down, you should suspect a plugged radiator.
3. The engine is consuming the coolant. This is created by a bad head gasket or a broken engine block and has some very specific symptoms. And water in the oil is only one of the many symptoms we look for. For the record, a head gasket can be bad and we wonít find a drop of coolant in the oil Ďcause all the coolant that is leaking into the cylinder is being sent out the exhaust and is not going into the engine oil system.
The first thing you may notice is the engine misses when it is restarted after it has sat for between 15 minutes up to 3 or more hours. When the engine is shut off, coolant is forced by pressure into one of the cylinders and when the engine is restarted, the coolant causes a miss until all the coolant is forced out into the exhaust. You may or may not see steam come from the tailpipe. STEAM FROM THE TAILPIPE ALONE IS NEVER ENOUGH TO CONDEMN THE HEAD GASKET. All cars have to deal with moisture in the exhaust on a cold morning start up, so steam from the tailpipe is very normal as the catalytic converter heats up and boils the water sent to it by the cold engine.
There are three tests we use to find a bad head gasket or being more precise, a coolant leak into the combustion chamber.
1. We use a dye and suck the fumes out of the radiator and run them through this blue dye. If the dye turns yellow, that means the presence of exhaust gases in the cooling system.
I must tell you I donít think much of this test. The positive results of this test mean nothing ALL BY THEMSELVES.
2. Apply pressure to the cooling system and watch the pressure gauge as you rev the engine. If the pressure rises quickly, that is a very good indication there is a combustion leak.
3. Fill the cooling system up with coolant, drive the engine till it gets good and warm. Park the car and shut off the engine. Make sure the upper hose is stiff and hard which indicates good cooling system pressure. Apply external pressure if needed via a cooling system pressure pump. After allowing the engine to cool for about 30 minutes, pull the plugs and crank the engine over. If any coolant comes blasting out of any cylinder spark plug hole, there is no doubt the engine has a combustion leak.
The coolant and water mix is pumped through the engine by the water pump. The job of the liquid is to pick up the heat and carry it to the radiator so it can be dissipated. The water pump can't pump foam, so they put anti-foaming agents in the coolant. We know that every car that overheats, does so because of the lack of coolant (because of a leak) or because of a restriction of the flow (closed thermostat, plugged radiator, or a water pump that's not pumping because of a drive belt that broke or an impeller that's come loose).
The thermostat's job is to open when the coolant gets too hot and let the coolant travel faster into the radiator. If it senses the coolant is too cold, it closes to slow down the flow to keep the coolant in the engine longer.
We all know that water boils at 212 degrees Fahrenheit. For every pound of pressure you put water under, it will raise the boiling point approximately 2 degrees. So a good 15 pound radiator cap will raise the water's boiling point 30 degrees from 212 to 242 degrees Fahrenheit. Add 50 % of coolant and the boiling point of the mixture is well over 260 degrees Fahrenheit.
We know that steam can't be pumped by the water pump, that's why we need the coolant to stay in a liquid form. It's important to know we want today's cars to operate at 220 degrees Fahrenheit . So if the coolant turns to steam too early because of a bad radiator cap or a weak mix of coolant and water, the car will overheat at 230 degrees or so, which leaves little room for an extended stop at a traffic light on a hot summer day.
Very few overheated cars are fixed with just a radiator cap and I've never seen a car fixed with a flush. Flushing a car to fix an overheat is like rinsing out your mouth with mouthwash to kill cavities. A flush is done after the repair, not as the repair.