"Over Heating"
It's no fun breaking down on the side of a interstate stranded 100miles from home or even locally with your temperature gauge pegged and steam blowing out the hood, so what causes this to happen.
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Thermostat
A thermostat controls the flow of coolant leaving the radiator entering the block threw the water pump and then reaches the thermostat, if the thermostat doesn't open enough or at all it can deprive the cylinder head of cool antifreeze cause it to over heat and possible warp the head and blown the head gasket, then it a down hill battle from there and the head need to be pulled, decked and head gasket replaced,in some severe case the block can be warped and then it's a complete over haul. Common symptoms would be foam coming out the radiator cap or antifreeze over flowing out the over fill tank.

Clogged Radiator
A clogged radiator can slow down or completely prevent the entire engine from cooling down, small ports inside a radiator allow coolant to flow thru, each port outside has small cooling fins that extract the heat chilling the coolant. If they get clogged your engine begins to over heat, sometimes simply pulling the radiator out and flushing both coolant flow ports out can get rid of build up, even a little dish soap added can help.

Collapsing Bottom Radiator Hose
The bottom radiator hose is the starting point of the flow direction & also the vacuum part, sometimes the hose can weaken and collapse preventing the water pump from pulling coolant which will cause your engine to over heat..so make sure to check it.

Low Coolant Levels
Having low coolant levels may seem like a no brainier but there's more to it then running empty. When your coolant is low it leaves big air pockets, the temperature of those air pockets far exceed the temperature of what the thermostat might be telling you depending on where the air pocket/pockets are. Always keep your coolant levels topped off to prevent this from happening.


Low Oil Levels
Yes, I know what your thinking.. "low oil levels"?!?.. and it may seem strange but oil actually removes roughly 75-85% of (waste heat)..what's waste heat you ask?? Waste he is the heat the engine produces such as bearing friction,ring friction,flywheel heat & heat soak from the head and block absorbing heat from combustion..So that extra quart your low could make your engine run 20% hotter. Always keep your engine oil between the dipstick markings.

Antifreeze To Water Ratio
This can also cause your engine to over heat and is probably one of the top common problems. Not having the correct Anti-Freeze to Water ratio can make your engine run too cool or too hot.The antifreeze to water mixture is 50% - 50%, and should never exceed more than 70% - 30%, the freezing/boiling properties of the mixture do not improve much after that point. Never put just water in the radiator,I've seen many people do this and it will cause prematurely failing water pumps and thermostats, just plain water rust out the insides of an engine, especially if your cylinder block is made of steel instead of aluminum.

Spark Plugs
Make sure your spark plugs have the correct heat rage for your engine, if you don't know you can always purchase a Haynes Manual or call up your local dealership.Too hot of plugs can cause lean conditions causing the engine to over heat and possibly detonate.

Advanced Timing
Advance timing is another thing that can cause your engine to over heat by promoting lean conditions, to find out if your timing is off simply use a timing gun by clipping it to the + &- battery terminals,then clamp the clip on #1 plug wire, press the trigger and aim the light at the crank pulleys timing mark and see if the timing line on the crank is within spec.

Water Pump
If your water pump propeller isn't spinning properly or the pump is leaking out the telltale pin hole then it's time to replace it. This can cause over heating.