New thermostat issues, engine running at 108°C

[mn94]

Hi all, that's my first post on the blog, happy to participate.
The thermostat related issue for which I'm seeking help is the following.
I own a Peugeot partner tepee petrol 72kw 1.6 from 2011.
The car had worked fine for years with engine temperature between 80 and 90°C.
Recently I got it to an authorised Peugeot workshop for checking some issues with the air conditioning (which were always present since i got it used). They found that the old thermostat needed to be changed due to a leak, so they did.
After this, the engine changed its working temperature. Checking with an obd reader now the engine runs at 108°C, even on the highway.
After a bit of serching, I think to have found the issue. The workshop installed a new thermostat version with a wax element which opens at that temperature.
However, this seems to be a piloted thermostat since it has both the temperature sensor and another plug at the place of the heater element. The heater element is connected with a two wire plug to a four wire plug and then to the electric system of the car.
I was convinced, also from other posts on this forum, that the ECU should control the heater element to keep the engine temperature between something like 85 and 105 °C. However the car runs continuously at 108°C.
I aslo tried to monitor the voltage at the heater element connector while the engine temperature was rising, disconnecting the connector and measuring with a multimeter. What i saw is a voltage of about 4 V all the way up to 105°C then a slight drop in voltage, something like -0.5 V between 105 and 108°C (maybe not significant). Also, without the heater plug connected the engine temperature rised as always.
Last info, since now the engine runs at this temperature the fan is very/too often on, starting only at 108-110°C and not before, but i do not know the fan start thresholds.
So the questions are:
1. Is this temperature dangerous for the engine?
2. Is the heater element non working? Or better, is the ECU not controlling it properly given those voltage measurements?
3. It seems impossible to find compatible thermostats with lower opening temperature. Are they not produced any more?
4. Possible solutions?

I checked the forum and found interesting discussions on the thermostat topic but none was answering this issue.
Any help will be greatly appreciated

[xantia_v6]

108° is not dangerous for the engine, but it does leave less margin for safety if something else goes wrong.

My understanding of these thermostats, based on our THP 156 engine is that the temperature control is mostly done by the wax element and the electric heater is mainly there to sharpen up the response by opening the thermostat a couple of degrees earlier when the engine is under heavy load. I would be surprised if it is capable of dropping the temperature by more than a handful of degrees. On our car, unplugging the heater connector makes no noticeable difference to the temperature gauge (or anything else), except that the ECU detects that the heater is open circuit and disables the A/C compressor.

How did you work out that the design temperature of the new thermostat is 108°?

[mn94]

108° is not dangerous for the engine, but it does leave less margin for safety if something else goes wrong.

My understanding of these thermostats, based on our THP 156 engine is that the temperature control is mostly done by the wax element and the electric heater is mainly there to sharpen up the response by opening the thermostat a couple of degrees earlier when the engine is under heavy load. I would be surprised if it is capable of dropping the temperature by more than a handful of degrees. On our car, unplugging the heater connector makes no noticeable difference to the temperature gauge (or anything else), except that the ECU detects that the heater is open circuit and disables the A/C compressor.

How did you work out that the design temperature of the new thermostat is 108°?

Hi, thanks for the reply.
I got the 108°C threshold because that is the temperature were the engine stabilise olus looking for a thermostat replacement i was finding only 105 or 108°C opening temperature, so i gussed it was the second case.
I agree that disconnecting the heater element did not cause any appreciable chnge, plus on my car, no fault lights went on.

[PaulC5]

If you post your vin it might help admin if they are able to look up information on your van.

[mn94]

SOLVED. So I eventually came around a solution for the issue. I'm still not sure if the heater element in the thermostat was not working because some failure in my car or because the car is an old model and thus it does not support that component.
However the fix I adopted was quite simple. I simply connected the heater element to the ground and to a positive 12V of the left headlight. The positive 12V goes on only when the car is turned on and it is off viceversa so it doesn't drain the battery. So, turning on the car will turn on also the heater which inputs an extra bit of thermal energy in the thermostat causing the valve to open before the cooling liquid reaches the 108°C.
Now the car runs on a fresh 80-90°C also while driving uphill.

[wurlycorner]

Interesting solution - though working around the problem.
Is it that they fitted the wrong thermostat?

[mn94]

Hi, surly the workshop installed a thermostat that is not the original version. Looking online, also on this forum, I understood that there should be at least 3 version of this part. However, searching for the substitution on different sites where you inser the car model and year, the cooler thermostat I was able to find for my car is a 105°C. Maybe the old and cooler thermostat was just discontinued.

[StefanoCola]

Hello mn94,
As I am having a similar issue - just posted here: viewtopic.php?t=86594
I wanted to ask you about more details about your solution
1. After starting the car cold, does it take longer to reach the operating temperature 80-90C ?
2. If you run with your lights off, does the heating core stop working and the temperature goes back up from 80-90C to 108C ?

Thanks a lot,
Stefano.