V70 Turbo - Overheating
 

All of a sudden ...

Engine temp has started to go into the red and warning message comes saying high engine temperature and the fan comes on.

It is possible to reduce engine temperature by running the interior heating system on full blast (old skool trick) and when doing this, the engine temp gauge goes back to the regular mid temp level (12 o'clock position).

On inspecting the engine after it goes into overheat, the water reservoir and hoses do not feel too hot. There is no boiling.

When you slowly open the water reservoir cap when hot, the water fills up and overflows.

Is this a water pump issue or a thermostat?

How much does it cost for a water pump replacement?

Water pump is my guess.

Usually, if thermostat will run cool and go up and down

is the top radiator hose getting hot,it could be a stuck thermostat. If the water pump has failed the rotor part would have to detach from the shaft and volvo pumps are usually 100% reliable. It would be much easier to split the thermostat housing and check the thermostat than start replacing the water pump.

That's true ;) My thermostats have always failed open, but they can fail closed too

I have seen engines and head gaskets replaced before when all that was wrong was a stuck thermostat.It is important to rule out the most obvious and simple faults first. the best thing to do is to run the engine from cold and wait for the thermostat to open and the top radiator hose get hot to prove it is opening.

Yeah, sometimes there might be a questionable water pump installed though. :teeth_smile:
https://www.youtube.com/watch?v=I6MkBufU8yU&t=53s

After 10 minutes or so, the radiator bottom hose and the top hose and the water bottle are hot.

Does this point to the water pump?

And what happens if you run it for longer? Does the engine really overheat, or is it just a faulty temperature sensor that is thinking the engine is too hot and putting the fan on and gauge too high for no real reason?
You said earlier "the water reservoir and hoses do not feel too hot. There is no boiling." so that sounds more like an incorrect temperature reading to me rather than a real overheating fault.

Yes, thanks for that. I will check the temp sensors. I have not had boiling water.

But I do have the condition that when you put the car's interior heating on full blast, you can reduce the temperature back to normal.

That would suggest to me that the temp sensors are working.

Does that make sense?

Had the same on my sisters S80 non turbo couple months ago ... changing the coolant sensor (about £20 - get one with the plug on!) fixed it nicely ... mind you the coolant was brown so I did a full flush and popped a thermostat in as well.

Whole job was under £50 in parts and it now runs properly ... Her's would also cool down if the heaters were opened up for a bit but then still went high.

Iain