How do I stop the coolant overheat message

CARL HALLIDAY

MEMBER
2003 PEUGEOT 307
1.4L
MANUAL
90,000 MILES

I have an issue, when I stuck in traffic my temperature gauge jumps from halfway to max with the stop light flashing and beeping at me and message comes up coolant temp too high.

After replacing the temperature sensor I realized this is not the cause.

However, after flushing the radiator I realized that the radiator fan is not kicking in until it is already saying stop too high,

What is causing this delay the radiator fan should kick on way before this ⚠️ warning?

I feel it is the thermostat, but as a new driver and know nothing about cars I would really like some advice.

Thanks in advance

6 Replies

CARADIODOC

MECHANIC
33,873 POSTS

I do not have access to service information for your car, but as a guess, it suggests you have a low-speed fan and a high-speed fan, and the low-speed one is not working. You may also have a single fan that runs at multiple speeds. We used to have two-speed motors, but some drivers complained about fan noise, so now a lot of manufacturers have gone to computer controls that provide continuously-variable speeds from real slow to full speed. Those computer controls cause a real lot of problems.

Do not replace the single-wire coolant temperature sensor for the dash gauge, (if your car still uses one). It is simply reporting the problem, so it is working properly. They have a very low failure rate anyway. It is the two-wire coolant temperature sensor that is for the Engine Computer. That computer is the one that looks at coolant temperature and determines when to run the radiator fan, and at what speed.

The best way to approach this is to use a scanner to view live data and see what coolant temperature the Engine Computer is seeing. That will also show at what speed the computer is commanding the fan to run at. Scanners give you a test mode to make the fan turn on so you can verify the system is working properly.