307 1.6 overheating

[Norrbjorn]

Hi!

So I have a 2005 307 1.6 petrol (TU5JP4) on my hands that overheats. Car is sitting in a parking spot at the moment, not ideal for major mechanical work.

From a cold start, the temp gauge suddenly jumps from coldest to max temp after about 5min on idle, turning on the STOP-light. At this point the cooling fan kicks in and runs about 5min after engine shutdown. Block feels warm to the touch, hoses and radiator are cold.

I replaced the thermostat and bled the system, hoping that it might help it make it to my shed but no bueno. Guessing the pump is shot.

So I ordered a timing kit + water pump, thinking I'll have it towed to my shed and tear it down there.
Before I pay for transport and whatnot, am I missing something simple here that one could check before moving it?

Cheers

[PaulC5]

Could be the coolant temperature sensor that is faulty. These are cheap enough so worth changing to eliminate it before the timing belt/pump. If you have a code reader that does live data you can see what its values are.

[Norrbjorn]

That's a good idea. I don't have a PC set up to run diagbox at the moment, but I guess I could just probe the existing sensor with a multimeter and see what it does. Looks like it is a standard NTC sensor.

[PaulC5]

To see the temp sensor live data a lower cost code reader is good enough, as an example https://www.gendan.co.uk/product_FXNT200.html but even this is likely to cost more than a new sensor.

[Norrbjorn]

Made meself a bit of a sensor stew this evening. Sensor is shot.
Strangely enough, it had sound readings up until it reached ~70°C where it would consistently read as an open circuit. Fingers crossed that's all it is as far as the "overheating" goes.

I also had a bit of a gander in the servicebox and found that according to the schematics there may be a thermoswitch wired in, sort of in parallell with the temp sensor. If the switch activates it grounds the signal, essentially giving a max temp reading since the measuring sensor is an NTC sensor.

I could not find one of those on this car though, but there is an empty threaded hole in the cylinder head, right next to the temp sensor. Guess they stuck an extra thermoswitch there for markets with slightly hotter climates than mine, as an extra precaution.

[PaulC5]

We had a 2003 C3 with the 1.4i petrol engine (TU3) and that had 2 temp sensors so maybe some of the parts are common but only 1 sensor on the 1.6i.

[ozvtr]

I also had a bit of a gander in the servicebox and found that according to the schematics there may be a thermoswitch wired in, sort of in parallell with the temp sensor. If the switch activated it grounds the signal, essentially giving a max temp reading since it is an NTC sensor.

That's known as the "low coolant level sensor". But it doesn't measure the coolant at all!! You are right, when the cylinder head temperature gets above 120'C it causes the temperature gauge to indicate full hot.
It has a blue electrical connector and it sits in a void in the cylinder head, BUT NOT IN THE COOLANT FLOW! (so if it's removed NO coolant comes out)
It's possible the sensor failed, and instead of replacing it, someone removed it and cut the connector off. There is no "fail-safe" mode for this one. So if it's removed...nothing happens.
If there is a spare 2 pin (but only one contact) blue electrical connector floating around that area...that's where it normally goes. But if you cant find it, it's probably been cut off!

Yes, it's basically the same arrangement as the the TU3JP engine.

[Norrbjorn]

Ah thanks for the info. Yes, I guess the switch belongs schematically to the coolant circuit simply because they spliced it to the coolant temp sensor circuit, even though it actually is more of a "cylinder head temperature switch".

I don't think this car has been messed with like that, my mum has owned it since almost new and all repairs have been done by the Peugeot dealer (before I started messing with it that is).
But since it was sold new in Sweden I guess it's not impossible that this sensor was excluded because it is a cold climate market. There is no loose connector around that place where the switch should be anyway, maybe I'll trace the wiring back once I get it back to the shed, I'll be spending a bit of time on it regardless.

Aside from the timing belt job there also seems to be some shenanigans afoot with the engine cooling fan. I think it's supposed to kick on at low speed as soon as the AC is switched on? It doesn't though, maybe something is wrong with the speed control circuit.

[Norrbjorn]

The dealer had a sensor in stock, so now the thing is driveable and I can get it out to the shed.

The low speed of the engine cooling fan is definitely forked, it starts to creep towards 100 at idle and fan doesn't kick in. Guessing it would eventually start in high speed if you waited. Will have to pry around the relays for the speed control.

[ozvtr]

there also seems to be some shenanigans afoot with the engine cooling fan. I think it's supposed to kick on at low speed as soon as the AC is switched on?

No. The fan(s) are controlled by the engine ECU and react proportional the the "high side" pressure of the A/C system. The pressure has to get above a certain point before the fan(s) will kick in. The high pressure line pressure is proportional to the load on the system. The hotter the day, the higher the load, the higher the load, the higher the pressure.

However, the low speed fan should kick in a little over 90'C (maybe 95 or so). If it's getting out to 100'C then you are probably right and there is a problem. If you idle the car for long enough the fan should kick in. BUT, even a fully functional cooling system may take 15 to 20 minutes of idling before the fan kicks in!!! A lot of people think that the cooling fan should run most of the time, but in practice, the fans dont run much at all.

There are many combinations of fan numbers and speed controllers! I do not know what arrangement you have. There are some fans that are controlled by resistors and relays, and some that have electronic speed controllers.
The greater number have relays and resistors and a typical failure mode is burn out of the relay contacts.

[Norrbjorn]

That's great input, thanks!
Yes, according to the schematic the ECU controls two relays, one of which has a resistor in series to the fan motor.

If I recall correctly there is an "actuator test" you can perform in diagbox to verify the function of low- and high speed. I'll start with that I reckon.