Q: Car stays cool while idling but once you start driving it it starts to overheat.

asked by on

Barely rebuilt the stock 305 in my car had a mechanic install it & everything car ran good for two weeks & then it started to overheat. I've replaced two thermostats, a jet temp cooling fan switch which kicks on at 190-195 & thats when I replaced the 1st one for one that opens at 195. Put in a brand new radiator flushed the system checked for air & inserted more coolant it seems to get not as hot anymore but it still is. Maybe should I try to replace the water pump? Thanks
My car has a manual transmission.

If the cooling fan is too small for the engine, then it may be enough to cool it at idle but not at higher engine speeds. Make sure you are not running under drive pulleys. You can check the coolant temperature difference between the top radiator hose to the bottom one using a laser type temperature tester.

This will tell you the temperature going in the radiator through the top hose and the temperature going in the engine through the bottom hose. If the temperature going in and out of the radiator with the fan on is more than a 20 degree difference, then the cooling system working okay and you may have a worn water pump causing reduced flow through engine. If you do not see the radiator temperature drop but by 5 or 10 degrees then you have a weak fan or clogged radiator. To have this issue inspected before making a repair, consider YourMechanic. They will be able to diagnose your overheating issue and let you know what should be done.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Car stays cool while idling but once you start driving it it starts to overheat.

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: steering wheel is locked but car turns on

The problem sounds like you have a broken engine serpentine belt. This would account for loss of steering, charge light on and overheat light all on at same time. Check engine drive belt and see if it broke or is...

Q: Car surges and wants to die while driving

This may be a sign of a dirty or failing mass air flow sensor. The mass air flow sensor is a unit in the intake system that monitors air intake as it is mixed with fuel prior to being injected...

Q: My left front turn signal and right rear turn signal don't flash and my right rear brake light doesn't light on my 2014 camaro. Th

Hi Dustin. Thanks for sending your question to us tonight. The blinker on the dash blinks fast when there is a light bulb on that side is burned out in most cases. This is likely the source of the turn...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
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...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...