PSA electronic thermostat operation

[gwest]

I have a 2013 Citroen DS5 turbo-petrol (THP155) that has covered 80,000 kms and I am expecting to have thermostat problems at some stage. My understanding is that the design of the thermostat has been progressively modified to overcome structural issues (cracking of the housing ) and that the wax pellet unit was replaced with an electronic one. But I have not been able to find any explanation of the workings of the unit, in particular whether the unit is controlling the temperature of the coolant entering or leaving the engine. My experience with the Rover K-series engine used in the MGF/Freelander (alloy block, steel liners) was that siting of the thermostat in the inlet, rather than the outlet side of the system provides a more stable control of the coolant temperature in the engine (http://web.tiscali.it/elise_s1/index.htm). However, the initial Rover design with the thermostat located close to the inlet to the water pump was changed to a remote position to overcome thermal cycling problems on warm up. I also have no idea of what the electronics actually do as compared with a conventional thermostat mechanism. Any enlightenment would be much appreciated.

[GiveMeABreak]

I'll need your VIN to determine the exact system fitted to your engine. Pop it up here (it will be automatically masked on post submission).

[xantia_v6]

The thermostat is not actually electronic, it is a conventional wax thermostat in a moulded plastic housing, but it has an additional heater element to heat up the wax capsule so that (at high throttle) the engine ECU can cause the thermostat to open before the coolant starts to warm up.

You cans read about my frustrations with this at viewtopic.php?p=560231#p560231 and the following page.

[GiveMeABreak]

So you have a Piloted thermostat with integral engine coolant temperature sensor:

Here is some general info:

(1) piloted thermostat.
(2) Coolant temperature sensor

The sensor is a resistive, negative temperature coefficient (CTN), sensor.

Roles:
The piloted thermostat permits:

• A faster increase in the temperature of the engine for better control of the exhaust gas pollutant emissions
• A higher engine temperature to reduce friction and obtain a reduction in fuel consumption

Coolant temperature sensor
The engine coolant temperature sensor informs the ECU of the temperature of the engine cooling fluid.

Key:
"A" Thermostat open (Piloted or non-piloted depending on the temperature).
"B" Thermostat closed.
(3) Wax.
(4) Heater element.


The wax (3) contained in the piloted thermostat (1) starts to melt from a temperature of 105°C.
During normal operation, the thermostat is not piloted, it regulates the coolant temperature at 105°C.

For full engine loads:

• The engine management ECU controls the regulation of the thermostat 85 at 105 °C
• The engine management ECU supplies the heating element (4) of the piloted thermostat (1) to add the 20°C that the coolant lacks to melt the wax (3)

The regulation of the piloted thermostat is controlled by an OCR signal of 100% at 85°C and of 0% at 105°C depending on the engine requirements.
The operation of the piloted thermostat is also determined as a function of the following parameters:

• Vehicle speed
• Engine coolant temperature
• Intake air temperature
• Ambient air temperature
• Knock detection
• Engine load
• Engine speed
• Engine management ECU temperature
• Temperature of the alternator

[gwest]

Thank you very much Marc- that is most informative. It makes the remote pressure release thermostat that MG Rover developed look simple in comparison. And can you tell me is the thermostat controlling the flow of water into or out of the engine?

[GiveMeABreak]

Some further info to explain how it is regulated:

"C" Partial load.
"D" Full load.
"T" Coolant temperature (°C).
"t" Time.

Time	Operating phase	Description of the operating phase
t0 and t1	Partial load	The engine management ECU does not activate the piloted thermostat regulation control; The regulation of the engine coolant temperature is performed at 105% to guarantee a saving in fuel consumption
t1 and t2	Full load	The engine management ECU detects a full engine load and controls the opening of the piloted thermostat by means of the internal resistor which melts the wax, simulating a temperature of 105°C. The engine coolant temperature decreases and stabilises at a temperature of 85°C
t2 and t3	Full load	The engine cooling is regulated at an engine coolant temperature of 85°C, to avoid an excessive engine operating temperature
t3	Partial load	The engine management ECU detects a partial load and no longer controls the activation of the piloted thermostat internal resistor ; The controlled thermostat again regulates the engine coolant temperature at 105 °C

Coolant temperature sensor
The NTC (Negative Temperature Coefficient) resistance value "R" changes in relation to the change in the temperature "T":
When the temperature "T" increases, the resistance value "R" decreases
When the temperature "T" decreases, the resistance value "R" increases

"R" Resistance ( ohms).
"T" Coolant temperature ( °C).

Temperature (°C)	Resistance (OHMS)	Tolerance(s) (in °C)
-30	88500	± 0,97
-25	65200	± 0,97
-20	48535	± 0,97
-15	36475	± 0,97
-10	27665	± 0,97
-5	21160	± 0,97
0	16325	± 0,73
5	12695	± 0,73
10	9950	± 0,73
15	7855	± 0,73
20	6245	± 0,73
25	5000	± 0,57
30	4028,5	± 0,57
35	3266	± 0,57
40	2663,5	± 0,57
45	2184,5	± 0,57
50	1801,5	± 0,57
55	1493	± 0,57
60	1244	± 0,57
70	876	± 0,57
80	629	± 0,34
90	458,9	± 0,34
100	340	± 0,30
110	255,6	± 0,30
120	194,6	± 0,30
130	150,5	± 0,70

[gwest]

Marc, it has me wondering what was so wrong with the software erroneously loaded into the DS5 between 2013-15 that resulted in the recall:
Overheating of the engine may occur due to a problem with the engine control software. Overheating of the engine may lead to engine failure.
The recall affects vehicles manufactured between 15. 5. 2013 – 24. 4. 2015.

[GiveMeABreak]

This recall won't affect your vehicle.

Your vehicle has an RPO code of 13255

This means it was built on 22 February 2013, so is outside of this specific recall window. Remember the warranty start date (29/11/2013) in your case is not the same as the build date at the factory. Recalls are based on the build date at the factory for a specific vehicle so that components / software implemented on each vehicle can be identified.

[gwest]

Thank you Marc. It has just occurred to me that I have been remiss in making a recent donation- this has been rectified. Anyone affected by the recall would be entitled to be really disappointed, to say the least. With electric switching of the water pump and fans I guess there is plenty of scope to overheat an engine, but I guess PSA is not going to be transparent on this issue. I can imagine that it would seriously affect vehicle values for owners with vehicles built during the offending period. My MGF suffered from softening of the cylinder head to the point that it was below acceptable hardness limits, and it would be interesting to know what sort of minimum hardness figures apply to the PSA alloy heads.

[GiveMeABreak]

Didn't the old Triumph Stags suffer with this issue - Aluminium engines or something - back in the 70s / 80s? if I recall.

There should be plenty of warning of an overheat and the fans should kick in in plenty of time with warnings and STOP messages etc., but these updated EP6CDT engines have a special low pressure die cast cylinder head as far as I can tell.

Thanks for the donation by the way - your member status has been upgraded, so if you need any current PSA part numbers or parts diagrams over the next 2 years, just shout.

[gwest]

Marc, I learnt something else about thermostats today, when I filled the newly assembled engine for the first time - all the coolant came straight out again!
I had bought a new thermostat from China, described as being suitable ("Thermostat Housing Water Outlet Fit For Citroen C4 MINI R56 R55 Peugeot 207 208 308 508 2008 3008 1.4 1.6 9808646980 V764558080 ") but instead of a blank stub 18mm diameter at 7 o'çlock, it had a patent open pipe. The only part number on it was PA66-GF30. My original thermostat had part no. V754184680-04. I have clamped on some rubber hosing with a plug at the end but am not sure if this is a sensible thing to do. I should think about fitting a coolant level alarm perhaps.

[GiveMeABreak]

HI

I just revisited this topic in light of your recent post and did a bit more research - and it seems there was a modification made to the outlet cooling housing due to various incidents linked to the engine coolant temperature sensor.

This only affected Euro 5 engines (which your is) and of course the modified housing or the repair that needs affecting will vary on the type of housing fitted, which depends on whether an Auto Box is fitted and whether there is a Turbo or if it is naturally aspirated.

Figure "A": Coolant outlet housing with removable engine coolant temperature sensor installed next to the bleed screw: Fitting correct; No operation is necessary.

Figure "B": Coolant outlet housing with integrated engine coolant temperature sensor and engine coolant temperature sensor fitted with a wire installed in place of the bleed screw: Fitting correct; No operation is necessary.

Figure "C": Coolant outlet housing with integrated engine coolant temperature sensor and bleed screw: Incorrect fitting; Carry out the repair.

I won't put up the repair procedure at this stage, but this may help you identify which version you have fitted to start with. If the repair then needs undertaking let me know. Some vehicles may have had the modification already undertaken post sale, so if you have 'A' or 'B' then the mod has been done, but if you have 'C', then it needs doing.

[gwest]

Thank you Marc, that is very helpful.
My 2007 Peugeot 207CC 1.6 VTi automatic had Type A fitted, with the removable temperature sensor and separate electrical leads for it and the heater element. There was no adaptor harness so I assume it was original? (VIN VF3**************[VIN obfuscated, can be read by forum staff]). The mistake I made was buying a new thermostat meant for the MINI R56 with an extra outlet for their expansion tank mounted on the LHS of the vehicle.

My 2013 DS5 THP1554 (VIN VF7**************[VIN obfuscated, can be read by forum staff]) puzzled me at first because I could not find the bleed screw, until I realised that it was on the same fitting as an electrical lead. Instead of a cross screw head the fitting had only a single slot, and to bleed the thermostat meant winding up the harness lead a number of turns. I thought that quite strange. So it appears to have the integrated ECT sensor AND the bleeder combined, and would match C if it had a lead connected to it?

[GiveMeABreak]

If the tank looks like 'C', then it would look like 'B' after the modification. 'B' is showing the tank after the modification was applied.

Just as an example with the DS3:

Here is the coolant tank from 2011 for the EP6CDT engine:

... and here is the coolant tank from 2018:

[Valex76x]

Searching to solve my issue I just read this thread. I have a Peugeot RCZ 1.6THP 156hp.
I have 2 issues, no idea if they are correlated.
-The OBDII app says I have an intake vacuum leak P2279, still not able to find the leak.
-Driving, the coolant temperature never reach 90°C. it stays around 60°C. Not moving the temperature goes up.

Need to mention that previously I had the check engine on and the radiator fan that was not stopping until I was not disconnecting the + of the battery and reconnecting it.

I just replaced the thermostat housing and the coolant. (Strange that I could fit only 4 liters instead of 6.2 I read should be). After replacing the thermostat and 8 hours without battery the check engine light is still not on.
I drove already 350km from the thermostat replacement.

Could be that the intake vacuum leak keep the engine in limp mode and the thermostat stays open?