Tip & How-To about Cars & Trucks

Engine Overheating even after you have changed the Thermostat?

So you flush the radiator, you change the thermostat in your vehicle and it still overheats. Or perhaps your heater doesn't blow hot air in the winter when you really need it?

You need to make sure the radiator and heater matrix (a small radiator made of plastic) is full of coolant with no air pockets. People get confused with filling the radiator and filling the overflow reservoir. There is a cap on the radiator, remove it and top it up, run the engine and keep topping it up. Also make sure that your HEATING in the car is on FULL heat and FULL fan. Squeezing the radiator hoses will help to dislodge air. The level will rise and fall when the thermostat opens up. Rev the engine a bit, top up one last time and when there are no bubbles and the opening is full, replace the radiator cap. Turn the engine off and then top up the overflow reservoir. Use antifreeze mixed to the manufacturers specs, usually 50/50. Please remember antifreeze is poisonous to humans, children and animals so wear gloves, don't ingest it and store it safely.

There is also a gadget that you can screw into the radiator cap to keep a head of coolant as the bubbles are coming out and stops spillage onto your garage floor or driveway.

Have a look at some of these videos.
https://www.google.ca/?gws_rd=ssl#q=burping+a+radiator&tbm=vid

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2 Answers

Heater doesn't get hot on 96 chevy truck. Blows good, just cold. Replaced thermostat, flushed radiator. Any ideas?


Air Temperature Control Blend Door Failure No Heat or no AC (dependes on where door sticks)

In all modern cars there is a tiny DC electric motor driven gear drive that moves a plastic door that blends heated and cooled air from the AC and the heater core, this is called (interestedly enough) the air temperature control blend door actuator. The motor that moves this door fails because the door starts sticking from warping, most common complaint is no heat but it can be no AC as well. To replace these parts (blend door and blend door actuator) you must remove the entire dash from the car. Always have this problem confirmed by a dealer or qualified repair shop as it is a very expensive repair.

Other causes of no heat in the cabin are engine thermostats that are stuck open (engine runs cold) or air bubbles in the cooling system.

Dec 06, 2012 | Cars & Trucks

1 Answer

temp sensor silverado


Yes it would overheat without circulation, but the coolant doesn't circulate through the overflow tank. That reservoir only gets coolant into it when the coolant gets hot and expands and pushes the radiator cap seal up to let coolant into the reservoir. When the vehicle cools down, the coolant contracts and the lower level in the radiator will siphon the coolant out of the reservoir back into the radiator. Coolant circulation is from the engine to the radiator and back into the engine...and also through the heater core.
You may have an air block in the heater core. Check by taking off the outlet hose at the firewall or at the engine and see if you have a slow steady stream of coolant, with the engine running and heater controls on high heat. If it was an air block, a steady stream should quickly start. If you get little or no flow, the core may be plugged and need flushing backward or replaced.

Nov 14, 2012 | Cars & Trucks

2 Answers

why would my heater blow out cool air when sitting still and then hot air when going down the road and then it's not all that hot


Try flushing or blowing high pressure air through the heater core lines. its sludge build up and need to be flushed through heater core only. check antifreeze fluid level. only put in straight antifreeze, do not mix. most people do not know what mixture should be, so be safe and add straight, it will not hurt it, i run 100% straight antifreeze and never had a problem or worry about it ever freezing and cracking my block, heads or radiator cracking.

Jan 29, 2012 | 2001 Daewoo Nubira

1 Answer

i put a new thermostat in my 1994 ford escort,and still dont have warm heat while my heater is on. How do I test to see if I have a bad waterpump?


If it where your water pump isthe vehicle would overheat. After you replaced the thermostat do you run the engine at idle with the radiator cap removed until the radiator fan came one? This will help push the air out of the system. There are two other possibilities. 1. The heater core is plugged. Back flushing the heater core may help remove the built up debris and get you heat again. 2. The blend door may not be fully transitioning from cold to hot. You should be ale to hear a district change in how the air sounds when switching from full hot to full cold. Let me know if you have any questions and I'll do my best to answer them. Thank you for using FixYa.com!

Jan 25, 2012 | Cars & Trucks

2 Answers

I have a 2004 chevy impala and i am having problems with it overheating. When it overheats the heater starts to blow cold air. Replaced the thermostat and had the coolants flushed. The car does not always overheat but the temperature is constantly changing from normal to above normal and heat is always changing back and fourth between hot and cold. Any suggestions?


Hello and welcome to FixYa! If you have overheating problem, it can lead to multipleissues. You may be running on low coolant that's why the vehicle overheats. Ifthat's the case, please add coolant and make sure that it sits on the rightlevel, too much coolant can cause overheating too for coolant will overflow. The vehicle may have a faulty or worn out radiator blowermotor that's why it overheats. If that's the case then you will need a blowermotor replacement to resolve the issue. If the radiator is clogged with dirt and rusts this issueoccurs too. The coolant doesn't flow normally on the cooling system if it'sclogged. If that's the case, I strongly suggest that you have the radiatorflushed to drain out dirt and rusts. If you think that the radiator served youenough then it's better to have it replaced. Please do check the radiator hoses, If you have worn outhoses it can cause coolant leakage which can result to overheating. A tiny holeis good enough for the vehicle to overheat. A faulty thermostat sensor can cause the issue too. If youhave worn out thermostat, the fan may not trigger that's why the fan won't workwhen under stressed conditions. A blown radiator blower fuse can cause thisissue too so I suggest that you check the radiator blower fuse and replace itwhen necessary. What causes the radiator blower fan fuse to blow? It's becauseof a failing radiator blower motor, If that's the case have the radiator blowerfan motor replaced. If the fluid in radiator doesn't circulate then it meansthat you have a blown head gasket or a faulty water pump. I suggest that you gofor the water pump replacement first specially if you think that it's near theend of it's service life. Usually, water pops out the radiator when engine isreved (a sign of faulty water pump and possible blown head gasket). Hope you find this information helpful enough and thank youfor using FixYa! Have a good one!

Jan 16, 2011 | 2004 Chevrolet Impala

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