A general thermostat query.....

[GiveMeABreak]

Now I'm back on the right page Some info on the thermostat for this engine:

Pressurisation	Cap with 1,4 bar rating
Opening of thermostatic regulator	83 °C
Fans 1st speed triggering threshold	96 °C
Fans 2nd speed triggering threshold	105 °C
Warning	118 °C
Post-cooling	105 °C (For 6 minutes )
Number x electrical power	2 x 150 Watts

The engine cooling circuit is subject to two operating phases:

• Temperature increase phase (Cold circuit )
• Temperature regulation phase (Hot circuit )

During the temperature increase phase (engine cold), the thermostat is closed, preventing the circulation of coolant towards the cooling radiator so as to allow the engine temperature to increase more rapidly.

Above 83°C the thermostat starts to open, the cooling circuit enlarges, the coolant fluid is cooled by the radiator, thus regulating the engine temperature.

The engine management ECU controls the fans via a relay allowing the fans to rotate at two different speeds according to the temperature of the engine.

• The engine management ECU activates the slow speed of the fans when the engine coolant temperature reaches 96 °C.
• The engine management ECU activates the fast speed of the fans when the engine coolant temperature reaches 105 °C.

This is for the DW10BTED4 engine - so what I said about the ensuring the right part number is obtained for the Engine Outlet Water Tank would be relevant Pete, given how the engine ECU manages the system depending on these values, although I appreciate it says "Above 83 °C the thermostat starts to open". So over to you, but don't forget you'll need new gaskets at 8 & 10 on refitting, as per the top diagram Pete.

Just one other thing - consider that the fault may also be with the blown air temperature sensor, which is another component associated with lack of warm air....

[milleplod]

Back at the keyboard!

The complete housing that I've already bought is part no. 1336Y9, with an 83deg thermostat inside it, so that's good! It comes with the sensor (no. 10 in the diagram) already fitted. Re the gasket at 8 Marc, the housing is complete with that stub pipe that a hose goes onto, so I'm assuming I'll not need one. My mate's hopefully doing it for me this weekend - I'll report back!

This is the part I've bought -

Pete

[GiveMeABreak]

Fingers crossed! No gasket needed if it has a new sensor included, that's a bonus and as for Gasket at 8 - it isn't actually shown on the parts diagram, so may be part of the joining hose.... I'll be interested to see if this fixes the issue.

[milleplod]

The instructions posted on my other thread refer to item 8 as the 'coolant outlet housing' when dismantling, and say to remove it......and then call it the 'thermostat with its new seal' when refitting! I wonder if there's a traditional-type thermostat behind item 8......with it having the 4 'ribs' on it, it does look as if a turn anticlockwise will give access to the main body of the unit. Intriguing!

Pete

[GiveMeABreak]

That rectangular gasket seal in your picture is referred to as Part 6: Engine Water Housing Seal.... so hopefully that is what they mean Pete!

[white exec]

Marc,

That's a reassuring set of temp figures you posted above.
Almost identical to XM 2.5...
Main stat starts opening at 85C, fully open at 100.
1st fan speed cuts in at 98C.
2nd fan speed cuts in at 101C.

The progressive opening of the main stat is obviously crucial to the engine achieving decent operating temperatures in cold conditions. Fully open (or stuck open) at 83C wouldn't be good.

[EDC5]

OK, but why such a low operating temperature?
Perhaps the large plastic thermostat housing (outlet tank) can't stand anything higher???

If I remember correctly the XUD9 had a completely metal thermostat housing, (with the fuel maze and filter atop) so I'm not sure if that's the reason. Perhaps it was a concern for warping the head or something that they had so opted for a lower temp compared to other manufacturers?

It would be interesting to see if the thermostat on the same engine but in a Ford or Volvo is also rated at 83 degrees.