[FIXED] 1.9 DW8 dasboard temperature cool. Checked and replaced thermostat, and coolant definitely hot. Temp sensor?

[kenbw2]

Within the last couple of weeks I've noticed my dashboard temperature gauge is often quite low - way below the 70 degree mark.

Thermostat:

- I've tested and replaced the thermostat: boiled it in a pan and it definitely opens and closes as it should
- With the engine warm-but-not-hot I disconnected the pipe at the thermostat housing that leads to the top of the radiator. There was a slight trickle coming from the thermostat
- I've filled the radiator by pouring water into the expansion tank until coolant came out of the same pipe. I then reconnected to the thermostat housing

I then took it for a blast (as much as you can take a DW8 for a blast) up a hill to ensure the engine was hot.

I disconnected that pipe, and coolant gushed out from the thermostat housing. The burns on my hand demostrate that the coolant was definitely hot and was flowing through the radiator, with the bottom hose being warm-to-hot too.

Temperature Gauge:

But still my temperature gauge sits well below the 70 degree mark - barely above minimum.

- The temperature gauge does fluctuate - sometimes visibly
- It never gets even close to 70 degrees
- It's not reliably at any position eg under load or at idle

Temperature Sensor

So my next suspect is temperature sensor. Where is this and is there a way I can test it?

There's these two plugs on top of the thermostat. (Un)plugging the green one clicks a relay on the left of the engine bay. (Un)plugging the blue one has no noticeable impact without the engine running.

[kenbw2]

Update for anyone finding this in the future.

I've replaced the blue one and all is well - dash telling me the engine's around 80°C, exactly where it should be.

My research online (including Peugeot ServiceBox) tells me:

- The green one is rated at 48°C - I *think* this is for the glow plug relay to control how long they stay on for.
- The blue one is rated at 118°C which controls the dashboard and *possibly* the injection timing, but don't quote me on that.

Swapping them out is an easy job. Just unplug and unscrew with a 19mm spanner. Keep the expansion tank closed or else coolant will spew out, and don't do it when the engine's hot.

One other thing I found was that newer DW8s don't have the blue one at all - they have a square green one that probably does the job of both. I checked scrap Berlingos between Y reg and 55 reg. The 52 plate Dispatch didn't have it either. I only found one on another T reg Dispatch.

I think the XUDs have both - even when searching against the DW8 Peugeot ServiceBox showed me a diagram with the characteristic XUD fuel filter.

For reference, prices I found for a replacement were £50ish from Citroen, £5 for the one from the scrappy. EuroCarParts doesn't list a blue one, but they do have the XUD one for £21, although I haven't confirmed that they're the same.