Q. I have a serious issue with my E36 328i Convertible. I bought the car at the beginning of the year, and after two months, the cooling system started to pressurise (a month prior to this I had fitted a metal impeller water pump and thermostat).

The company I bought it from took it back, fitted a radiator and it was fine for two weeks... then went again, chucking water out of the rad cap, with pipes rock hard etc. They had it back again and fitted a viscous fan to it. It was fine for two weeks and then went again.

I then started to look into it myself, and found my thermostat had jammed and there was gunk in the housing, indicating stop leak had been added. I fitted a new thermostat and it was still faulty. So I took it to my local garage that sniff tested it, and said it couldn’t be related to a cracked head or gasket. They found the thermostat I fitted had jammed again (probably because of stop leak being in the system). It was okay for about a week, then went again.

I put a vast amount of cooling system cleaner through it, and no rubbish came out (I thought maybe a blocked waterway). I also replaced the heater control valve at the bulkhead as this was suggested to me.

Since August it’s been in storage and since then I have had the head off. Gasket looked okay, head pressure tested, not cracked, skimmed (only 3-thou out), and all the water galleries looked okay, so I put it all back together. It’s still pressurising once up to temperature, chucking the water out the cap and pipes get rock hard. Now it’s also steaming a lot out of the exhaust (but runs fine; I torqued everything down accordingly when rebuilding. I’m a mechanic myself by trade). It’s a Nikasil block engine. The bores look fine, I’ve never had trouble starting it, no oil use, no poor idling. I had another mechanic look at the bores and he said they looked fine too. The water is circulating around the engine okay as I checked this with the top hose off, running water into the rad, with the engine running. The only thing I can think of now is if the block’s gone porous or cracked.

I’ve now spent in excess of £500 to no avail. Problem is, the car’s only done 52,000 miles so I don’t want to be putting in a secondhand engine with twice as many miles.

Mark Wearing, email

A. This is a tricky one. Because it’s still the original Nikasil block, the bogey of alloy sinking between the steel liners won’t be happening. Is the heater blowing hot? If it isn’t, then you have a massive air lock. The best way to refill a BMW cooling system is via the top hose. Disconnect the top hose from the rad, slacken the thermostat end, turn the hose through 90 degrees so it points upwards and tighten the hose clip. Add coolant through the top hose with the rad cap off. As soon as the level in the expansion bottle gets to just over half way, refit the cap and tighten by hand. Continue filling slowly - you can do this with the ignition on and the heater set to hot, but the valve should be open anyway without power. When coolant starts to dribble from the top radiator elbow, you know the engine and radiator are full. Refit the hose, fire up the engine and hold it at 2,500 rpm until the heater starts to blow warm air.

In the past I’ve had a couple of problem cars and I’ve drilled a 3mm hole in the thermostat outer ring, refitting the stat with the hole at the top.