Pre 2002 MG Thermostat replacement.

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. :broon:

Excellent!:yesnod: No more leaks?

David Aiketgate wrote: Excellent!:yesnod: No more leaks?

I bled the air out and let her run for an hour. After 40 minutes the fans came on then went off. It didn't overheat, the rad was hot and the heaters stayed hot too. I haven't done a run yet. I'll do that tomorrow. No leaks apparrent at this time David. So far, so good. :broon:

After it had cooled I topped up the coolant an inch and noticed a 'pssst' as I undid the new cap.

In the pic above you can see the crud I dragged from the coolant rail. I can only describe it as little lumps of 'red clay'. Anybody seen that before?

I've seen that in many engines, although generally you find more in cast iron engines. It is a mix of rust from ferrous components, deteriorated anti-freeze, and silt and crud from water. It could also be the remains of K-Seal or a similar product used by a previous owner or mechanic. With the amount visible in your engine I wouldn't be surprised if that is what it is.
In the old B-series that have the cooling tap in the block it is common to find the tap plugged with similar brown crud. Once you unscrew the tap you often have to take a screwdriver and dig out the waterway behind. It can get so bad it effects the cooling, usually in areas where the water passages are narrow (and cooling is most critical!) like the head. :pinch: