Coolant boils before fan turns on
 

Hello!

I have a 2001 V70 XC.

A while ago, the fan started running non stop on full speed, even with the engine off and key removed. It did this for about a week (I had to unplug the fan when I parked.) and then it stopped turning on at all, and overheated. At this point, I had no antifreeze, so I refilled the cooling system with water to get me home.

Research pointed me to a bad control module, so I replaced the fan & module and flushed the system, refilling it with 50/50 mix.

Now, the fan turns on when I turn on the A/C. But it doesn't seem to be on a very high speed. As I let the car idle, I'm watching the coolant temperature on my OBDII scanner. Once it reaches 103°C, the coolant starts boiling. When it reaches 105°C, the fan turns on, but it still seems to run at a slow speed. At this point the fan will run until the temperature drops to around 102°C, then the fan turns back off.

Any ideas what I should do next? A friend of mine suggested it could be the temperature sensor. Does this seem like the kind of thing a failing temp sensor would cause? Any other ideas?

Thanks!

Did you replace the thermostat when you did the coolant change? ECT sensors do fail, particularly when corrosion builds up on the sensor's surface - a common issue. Keep in mind your OBD reader is using the sensor to report the temperature so if the sensor is off, so are your reading. The low fan speed should kick on around 90C (195F or so) and the high speed around 100C so you may have an issue with the fan assembly, relay or the ECT.

I'd probably start by replacing the ECT ( about $50 US), the thermostat ($15 US), the overflow reservoir cap (another $20 US) to baseline the car, then start doing some diagnostics on what controls the fan speed. (separate from the AC, which I believe is its own signal).


https://volvoforums.com/forum/volvo-...estions-60553/

Sorry for taking so long to reply. I've really been struggling with bills and haven't been able to work on the car much...

I did not replace the thermostat. I replaced the Temperature Sensor, and that didn't seem to make any difference.

However, I tried starting the engine without the temp sensor plugged in and the fan started running. I plugged the sensor back in while idling, and the fan continued to run. I turned off the engine, and the fan turned off a minute later. Now, the fan is running whenever the engine is on, and the coolant temperature is not going above 82°C. (Before the fan was not turning on until the coolant started boiling at around 105°C.)

Also, the temp gauge on my dash isn't moving, but I suspect that 82°C just isn't hot enough to move the gauge...? Before, it would stay right in the center of the normal range, even when the coolant was boiling.
Seeing as the temperature is now staying too low, I suspect it's the thermostat. I've ordered one, and it should be here later this week.

But I don't understand how that would affect when the fan turns on/off. Shouldn't the fan turn on when the coolant is around 95°C, regardless of what the thermostat is doing?