My 2002 MGTF thermostat was leaking.
So, I decided to change it for a complete new one (usually they're as much as 55 pounds, but I found one on ebay for less than 20).
I was told that it was best to remove the inlet manifold and change the gasket whilst doing the job and to give it at least 3 hours timeframe to do. I managed to get lucky and do it in less than an hour. Probably because I decided not to remove the inlet manifold. Here's how I changed the stat.
I backed the car up onto some wheel ramps intending to try and do the job from underneath. In the end, I removed the expansion tank and did the job mainly from there. Other than a TF160, when you're replacing the whole thermostat unit there's only two bolts you need to remove. The 160 has an oil cooler bolted on top of the coolant rail which makes things tougher to get at.
Be prepared to lose 3 or 4 litres of coolant doing this job.
You can now lift the old stat out and compare it with the new one that you're going to fit.
The space where the old stat was.
Clean out the pipes on the coolant rail and the waterpump before inserting the new stat. The left side pushes into the coolant rail below.
The right side pushes into the waterpump below.
Bolt the stat onto the engine block like so.
Resecure the hose to the thermostat.
Resecure the 13mm coolant rail bolt.
As you can see in the pic above I only had one bolt. But there's room for two. So I improvised and added another. This held the coolant rail securely.
bleed all the air from the cooling system.