The 75 and ZT Owners Club Forums - CDTi Thermostats - Why they fail, how to diagnose yours and how to fix.

If you have a 75 or ZT CDTi, you may have noticed your temperature gauge never reaches the middle of the dial.

It should do this during normal driving - 3-5 miles of normal driving should see you have a healthy 9 o'clock reading on your gauge. If not, read on!

Why do they fail?
It seems the BMW thermostat fitted to the M47R suffers with sticking open - it's reported widely on BMW owner's clubs, on Land Rover forums (the Freelander TD4 shares this engine) and of course on this forum in the many threads discussing the issue.

When your thermostat is stuck open, the engine will be over-cooled and you'll suffer with low running temperature - reducing fuel economy. Normal operating temperature for the M47R (when driving) is usually around 85-90 degrees Celcius, with this increasing when sat in traffic or idling with no movement. The fan will cut in to prevent overheating if this is the case, however when on the move the CDTi won't make enough heat to make this a necessity.

9 o'clock on the temperature gauge is 75 to 115 degrees C - the chances are if you reach 9 o'clock and this doesn't change when driving your thermostat is OK. You can test the exact running temperature by going into the integrated diagnostic mode built into the Instrument Pack - T-Cut has made an excellent guide on this subject: https://www.the75andztclub.co.uk/for...38&postcount=1

How do I fix this?
Luckily, fixing this issue isn't as hard or complicated as it used to be.
If you're after restoring normal functionality with the minimum of fuss, you can fit the thermostat from a Renault 5 into the top radiator hose (at the engine end). This is a simple affair, as detailed below:
- Cut through steel band securing top radiator hose to engine coolant outlet
- Fit thermostat into top hose, with the copper bulb facing the engine (You'll need to grind the collar of a standard Renault thermostat down a little, however the kits I supply are already ground ready to fit)
- Secure the thermostat with a Jubilee clip, and use another Jubilee clip to re-attach the pipe to the coolant outlet
- Fill the header tank back to the 'maximum' position, and run the engine for a couple of minutes to circulate coolant. Check coolant level and top up if needed.
- When using the car for the first time after this job, check the coolant level once a warm-up cycle is completed (make sure your coolant is cold again though, hot coolant can scald if the cap is removed when the system is under pressure).

I supply both the OEM thermostats, and the Renault 5 items.
Renault 5 Thermostat Kit, including pre-ground thermostat and 2x Jubilee clips: http://www.dmgrs.co.uk/collections/t...tat-89-degrees
OEM Thermostat (BMW): https://www.dmgrs.co.uk/products/r75...evised-version

*NEW SOLUTION AVAILABLE - V3 ORIGINAL STYLE THERMOSTAT*

We've worked with a major thermostat manufacturer in China to have a revised OEM-style thermostat made - this has been dubbed the 'V3' item (early diesels used V1, which didn't suffer with many problems - then V2 replaced it, which suffers with opening early).
This item shouldn't suffer with opening early as the V2 items do.

This item is a bargain at just £29.99 - available here: V3 Thermostat - CDTi 75/ZT/Freelander

I've also written a How To about changing the original thermostat:
https://the75andztclub.co.uk/forum/s...d.php?t=245051