Electrical water temp thermostat.

discv · Unread post by **discv** » 11 May 2021, 13:12

1.4 petrol 8v 2007

The simple solution to my problem would be to replace the electrically operated thermostat with a conventional type. I've seen a couple of old posts that seem to suggest this is possible.

Any ideas please.

discv · Unread post by **discv** » 11 May 2021, 17:08

A bit more info.- I replaced the thermostat housing complete with a new temp. sensor. I also replaced the thermostat assy. complete with a new yellow connector, which I think is the heater.
I have the fault code P0598- Thermostat heater control circuit low.
The stat makes no attempt to open. The cabin heater works ok but things start getting hot!
I have forced the old stat into the open position, refitted it and the engine runs ok but obviously somewhat colder

white exec · Unread post by **white exec** » 11 May 2021, 19:37

Unusual for a new thermostat not to function.
The opening of the 'stat does depend on it being properly surrounded (on both sides) by coolant.
Is it possible that the system wasn't properly bled after fitting, and there's an air pocket trapped in this high-point of the system?
If you've now got the new one off the car, test it in some hot water - it should open around 90degC (haven't checked the precise figure for your car).

discv · Unread post by **discv** » 12 May 2021, 11:00

If my understanding is correct, the option to test the stat in hot water is not on. Some form of electrical signal is required for the stat to operate.
Now if I could find out what sort of voltage this signal is- then maybe I could 'hot wire' the stat.
P0598 seems to indicate that there is a problem a problem with this signal.
Your comment about trapped air is interesting- the system was fully and carefully bled, but the stat remaining closed seems to cause an airlock.
All of which is taking me back to square 1. My initial port of call was head gasket- which I replaced, skimming the head at the same time.

I really need all the help I can get on this one!

white exec · Unread post by **white exec** » 12 May 2021, 13:58

" 1.4 petrol 8v 2007 "
Can you confirm what car we're talking about here, and its VIN number, so we can look out some details?
Thanks.

discv · Unread post by **discv** » 12 May 2021, 14:24

VF3**************[VIN obfuscated, can be read by forum staff]. Thanks for hanging in with me!

wheeler · Unread post by **wheeler** » 12 May 2021, 17:54

Many 'electrical' Thermostats are actually just normal thermostats with a little built in heater element that can be activated to make the wax melt faster to control the opening of the thermostat. Not sure if your car has this type or not.
Have you tried operating the start with diagbox? You can connect a noid light in the electrical connector in place of the stat to see if the signal is being sent to it when you activate it as you wont know it is activating because its silent.

GiveMeABreak · Unread post by **GiveMeABreak** » 12 May 2021, 18:20

So you have the TU3A Engine.
Moderator edit:
and a 207 5 DOOR SALOON 1.4 i 75 (TU3A) Manual gearbox 5

This has a thermostat at the front which is available separately:

Item (6) Part: 1336Z2, £72.54

discv · Unread post by **discv** » 12 May 2021, 18:44

"Have you tried operating the stat with diagbox?"- quote
Diagbox reports a fault with the heater circuit. I am certain that that stat is receiving no signal.

"Many 'electrical' Thermostats are actually just normal thermostats-----Not sure if your car has this type or not."-quote
I'll chuck it in hot water tomorrow and see what happen!

The stat part no. that Marc quotes is indeed the item that I cannot get to function.

I'm going to try and fit a standard mechanical stat. tomorrow meant for an earlier engine. Part no. 1336Q2. If it works I think the trade off will be a constant MIL

GiveMeABreak · Unread post by **GiveMeABreak** » 12 May 2021, 20:32

Until your next MOT! I don’t think they allow any engine warning lights on for a pass - will have to check...

Unread post by **xantia_v6** » 12 May 2021, 22:13

On the EP engines, you can disconnect the thermostat heating element and replace it with a 50? 5W resistor to keep the ECU happy. Maybe it would also work with your engine.

discv · Unread post by **discv** » 13 May 2021, 13:09

So, the stat does not open on being plunged into very hot water.
The heater in the stat housing shows continuity- so no chance of cheating the ECU with a resistor. Good tip though!
I have yet to try and fit the mechanical stat.

Meantime- could anyone find me a diagram so that I can look for a wiring fault between the ECU and the stat heater element.

Unread post by **xantia_v6** » 13 May 2021, 20:39

discv wrote: 13 May 2021, 13:09 So, the stat does not open on being plunged into very hot water.

That sounds like a faulty thermostat.

white exec · Unread post by **white exec** » 13 May 2021, 22:26

It does. Temp must be near 90degC though.

discv · Unread post by **discv** » 14 May 2021, 17:14

So the electrical stat has been replaced with a mechanical one [part no. as noted above] and it is opening in the expected way.
I believe the electrical stat is not working because it has no/low electrical supply.
However, in my bones, I have a nagging suspicion that I am dancing around with a hairline crack in the cylinder head. This may be causing problems with the temperature sensor

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Electrical water temp thermostat.

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