Skip the auto shop - Our mechanics make house calls

Q: Top radiator hose is cold while the lower is hot

asked by on

I believe it may be the new thermostat that installed

My car has 107000 miles.
My car has an automatic transmission.

You may be correct that the thermostat is stuck closed. One way to test a thermostat is to put it in a pot of water and bring the water temperature up to the thermostat opening temperature. This is imprinted on the thermostat. If the thermostat does not open or opens more than 5 degrees late, then have the thermostat replaced. If the thermostat is open as it should, then you have another issue of no or low circulation in the system.

This can be a restricted radiator or a water pump with worn off impeller fins. If you remove and test the thermostat to be okay, then flush the radiator with both hoses disconnected to see if a lot of scale or debris is blocking it using a garden hose. It is harder to test the water pump. You will need to remove it to check it, at which point you may as well replace the pump. The radiator can be checked for hot and cold spots when it is running to see if it has plugged passages and needs replacement. If you want to have this issue diagnosed before moving forward with any repairs, a technician from YourMechanic can come to your home or office to inspect your car and let you know what adjustments should be made.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: I have a slight wobble in crank shaft pulley will replacing it fix my problem? Its a 2000 lumina with 76,000 miles. thank you

Hello. The crankshaft pulley and harmonic balancer is one unit on your vehicle. There is a strip of rubber that separates the two components, that will perish over time. This is typically why it begins to wobble. You will need...

Q: Temperature guage fluctuates between mid temp (normal running) and cold at higher speeds

This may cause other engine problems relating to the engine not warming up properly to run at normal operating temperature. There are many other systems that run based upon engine temperature and coolant temperature. Fuel injection and timing for example,...

Q: Dash pad curled up

Once plastic warps like you described, there is not much you can do. You can have an interior specialist look at it, maybe they can repair it. The only other way would be to replace the dashpad.

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.