Like several others here and on the MG forums (those that have Td4s in their vehicles), I've been suffering a lazy thermostat recently. This was really brought to light this week when the temperature dropped and I had virtually no hot air, and the temperature gauge hardly got up to 1/4.
Daunted by the tales of taking the belts off, crankshaft pulley off, water pump off, bending the metal coolant rail that bolts into the thermostat housing, etc, but, knowing I had to do this job, this is what I found when I did the swap this afternoon: it can be done without removing ANY of the belts, pulleys, water pump, etc!
Firstly, get your thermostat/housing from Island 4x4. £35 delivered, which was about the best price I could find. Tis a genuine replacement too.
In addition to your normal tool kit, arm yourself with a set of Torx ratchet spanners (you actually only need an E8). A 1/4" drive E8 Torx socket is very handy too.
Jack the front up and remove the following: engine undertray, acoustic top cover, air filter cover, turbo hose that clips onto the MAF sensor housing, driver's side wheel and side splash shield.
Drain the coolant by removing the rubber hose from the solid metal pipe under/in front of the engine. Next, remove this metal pipe completely - 3 x 8mm bolts and a hose clip where it connects to the rubber elbow hose that goes into the thermostat housing.
Place a trolley jack under the engine and then undo the 15mm bolt and the 18mm nut on the O/S engine mount (the two you can easily get to by the ABS block). You can now raise the engine up and lower it down as you need to.
Working above and through the steering rack hole you should now be able to tweak the four Torx bolts out using a combination of the E8 ratchet spanner and the E8 socket. It takes a while, but the ratchet spanner is well worth the investment here. Also remove the 10mm bolt holding the metal coolant rail into the thermostat housing.
Once it's all undone, you should be able to pull the thermostat forwards a bit. It probably will get stuck on the engine mount and coolant rail, but if you raise the engine up as much as you can on the jack you will just get enough clearance to a) move the coolant rail back a bit, and b) pull the thermostat clear of the water pump. It'll ultimately only go one way: down. It can then be pulled out through the steering rack hole though.
I'd left the rubber hose on it at this point. So I swapped that over and reversed the procedure to get the new unit back in position. Once I'd juggled the engine height about a few times I got all four Torx bolts back in plus the coolant rail bolt. Then I did the engine mounting bolts, then the plumbing and the turbo pipe.
Sadly that's where I ran out of daylight. So I have about an hour's worth of work in the morning to fill the coolant up, and put the other bits back on, but, barring any leaks
it'll hopefully be OK. I'll update this post tomorrow.
I just wanted to share my experiences with this job so far (about 3hrs of work currently). I'm not playing this one down at all - it IS a pig of a job, but it CAN be done without removing too much other awkward stuff. Probably important to know if you're planning to do this at the weekend...