Why does a car overheat?

Answer 1

no coolant or you have a bad thermostat and or bad water pump .

Coolant could be low. Thermostat could be broken. Water pump or fan may not be working.

I had a 2002 Vauxhall Corsa which was running hot and it turned out to be the water pump which needed replacing.

Causes for an overheat: low coolant, failed water pump, plugged radiator, failed headgasket, inoperative radiator fan, stuck thermostat, missing belt, etc

First confirm that the engine IS actually overheating - steam, no heat to the interior etc. Sometimes a temperature sensor will fail and give a misleading 'overheat' reading on gauge. For that matter sometimes the gauge can fail and give the same misleading reading. Check that the cooling fan comes on when the engine temperature starts to rise above 'normal'. If not check (in order) fan fuse, fan relay, fan sensor, fan. Real overheating is caused by a lack of coolant AND/OR lack of coolant flow. Modern cooling systems are 'closed'. In other words there should be little or no loss of coolant. If the level is significantly low you have a leak....either external or internal. With the coolant topped up to the correct level and the radiator cap on, run the engine and look for visible leaks...hoses, valves, radiator etc. Internal leaks, eg. head gasket will usually be accompanied by white exhaust smoke (steam), hard starting, rough running and bubbles in the expansion tank. Sometimes, though NOT always, you will find the engine oil has a milky look and/or engine oil will be mixed in with the coolant. == == Lack of coolant flow can be caused by anything in the system that causes an obstruction......in order of common occurance......thermostat stuck closed, radiator blockage, heater core blockage, water pump failure. One last point. because of design considerations many vehicles have the radiator mounted at a different level than the uppermost coolant passages in the engine thus trapping air in the coolant passages. In short the system must be bled of air in order to properly fill with coolant. Such systems will incorporate bleed screws usually in either the top/side of the radiator, the top hose, the thermostat housing and sometimes in all of these points. To bleed out the air do NOT run the engine as you fill the radiator. Instead, open all bleed screws. As you fill the radiator coolant will run out of one or more bleed points. Close this bleed point(s). Continue to fill until coolant escapes from the next bleed point then close that one. Proceed until coolant has escaped from ALL bleed points then continue to fill to the correct level. The expansion tank will have minimum and maximum level markings. Fill only to the minimum level mark with the engine cold. Explaining how to check each of the individual components would take up more space than I have so if the above doesn't help email me at seahog@btinternet.com.

AnswerHere's a list of 7 items to check. It's pretty much standard for all engines.

Check the oil level add as needed. Check the water (and antifreez) add as needed Check the rediator cap. re-place if it's old or missing the seal gasket Check the thermostat. replace if old or not working See that the belt to the water pump is adjusted properly Check to see if the water pump is working. Check the radiator. Make sure it isn't clogged

It's a good idea to visually check the oil, water, belts and hoses everytime you fill up. It takes less than 2 minuites and could save you large amounts of money and headaches.

Answermake shure that the seal on the cap are not cracked Answer1 insufficient coolant in the system. 2 water pump drivebelt defective or not adjusted properly. 3 radiator core blocked or radiator grille dirty and restricted. 4 thermostat faulty. 5 fan blades broken or cracked. 6 radiator cap not maintaining proper pressure, have the cap presure tested. AnswerCheck fuses for the electronic fan. AnswerOne other thing to add o this good information. If after changing coolant or any time you have worked on the system, you must bleed all air out of the cooling system. Trapped air can cause an air pocket which will cause a hot spot and overheating. Some cars have bleeder screws and some don't. Check your owner's manual. If there is no bleeder valves and you suspect trapped air, park the car uphill or jack up the front, start the engine with the radiator cap removed and run until it reaches operating temp. This will allow trapped air to escape. Also make sure when replacing the thermostat and radiator cap you install the correct ones. AnswerLot of good answers here. I have found evaporating cooling fluid to be a problem when everything else is working correctly. Common cause for this is too much water, not enough antifreeze. Evaporation is called "boil over". Adding antifreeze to water increases its boiling point. Since water boils at 212 degrees, and (my car) optimal operating temperature is 190 degrees - there is a thin line from running normal to "boiling over". Solution - the mix in the radiator should be 50% antifreeze and 50% water. To get the correct ratio antifreeze to water, buy a coolant test kit or buy your coolant in pre-mixed bottle. a different situationwhat if the electric fans are not coming on? Answer

In that case, (Fans not running), it may be a blown fuse, bad fan motor, or a bad thermal sensor.

Answer. If fans are not coming on, check coolant temp switch. I ahd same problem with my car. I had my cooling fan direct. Had a bad coolant temp switch

Answer:

I experienced one time an engine that was overheating due to a slipping overheating transmission. Although some diagnostics can be obvious, sometimes there is a curve ball.

If the fuel economy has dropped also?

We've seen a few older cars with cracked head gaskets - the combustion stroke, gasse are 100's of PSI. And that pressure blasts into the water jacket during operation, causing the coolant to stop circulating - normally due to extreme over-pressuring.

This should show itself as bubbling through the radiator cap - but to diagnose properly, you need a small test kit to check. (Eric the carguy and Scotty Kilmer have a video about it on ewe toob) Being that I've rebuilt only three engines in my life, it's safe to say that all the answers above are more likely - especially for a japanese car, but the septic-tank-mobiles and our aussie rubbish - this is pretty comon.

Also, check to see if the fan shroud or parts of it are missing.

Bad thermostat, water pump, heater core, or radiator blockage. Usually in that order of likelihood.
Possible causes: 1) loss of coolant 2) something clogging the coolant lines or radiator 3) stuck thermostat 4) wrong thermostat installed (wrong temp rating) 5) damaged or improper radiator cap Also, forgot to mention poor coolant circulation (water pump)
thermostat?
numerous reasons...thermostat,water pump could be going bad, no anti-freeze in radiator, no water in reserve tank...this should be checked out by a professional or you could be stuck somewhere.
It depends on the engine type:

For a normal radiator cooled engine:

Lack of coolant

Punctured radiator

Radiator fins clocked with debris

Corrosion inside radiator that leads to blocked galleries in the radiator

Lack of engine oil

Lack of airflow around the engine block (contributory)

Cracked Head(s)

Head gasket failure

Warped engine block

Old coolant

Water pump failure

Oil pump failure

Blocked cooling galleries in engine block and head(s)

Thermostat failure

Cooling fan failure

Air cooled engine:

It depends on the cooling design. Mostly it's due to lack of airflow, or in some cases oil, cracked head/gasket failure.
When you drive too long.