If I was you I would start by removing the stat. This should make the engine warm up a lot slower (the only reason for the stat is accelerated warm up). While you are warming the car up take it easy and don't give it lots of revs for long periods.

Is your header tank at the highest point of the system? If so I would start the car with the header tank cap removed. As the engine is running, work your way all the hoses on the engine, giving each one a good hard squeeze in turn and checking for any bubbles in the expansion tank and keeping it topped up. You should be able to see some water movement in the tank depending on how you have configured it. You should be able to leave the car idling without it boiling over without the cap on.

Putting the cap on - if it is a 14psi one the the boiling temp of the water will be raised to 119C.

I wouldn't run the car without the stat on the road - as the last thing you want to do is overcool it during the early stages of warming up. If you do decide to remove the stat, put a metal disc with a hole in place of the stat as this will provide with you some flow resistance in the system.

Hi David,

yeah the header tank is a few inches higher than the engine. I'll have a look at the stat tomorrow afternoon now. I need to get it out of the garage first cos i nearly flooded it the other day fiddling with the radiator hoses!

Great advice there, davidmurray, I'm sure it will be helpful to me as well when it comes to filling the cooling system.

I would not consider a "no thermostat" option so risky. I had a stat stuck open on my daily Nissan Primera W10 for several years back in the day. Imagine my joy when having replaced the stat the heater started blowing heat after just 2 km instead of 10! No apparent damage to the engine though.

OK, earlier I removed the stat. Put it in a pan of boiling water, and it opened about 2mm, but only after a few minutes at a rolling boil.

I take that to mean it's had it, as according to BMW it should open at 85 degrees.

So anyways I cut the centre out of it (the outer ring supported the rubber seal) and refitted it. Refilled the water and ran it. After manipulating the rad hoses to make sure there were no airlocks, the rad got nice and hot, and no more boiling up.

So well done guys - stuck stat it was! Now I just have to find a replacement at a decent price.

Aerosam - glad you got it sorted - now you just need to save the pennies for a new one:p

Alga - having a stat in there that is jammed in is fine - remvoing it totally is more of an issue. The stat acts as a restriction in the coolant flowpath and as a result helps to balance the flow to different areas of the block. If you remove the stat then you give the water an 'easy' path through the engine that can result in the engine overheating becuase you don't pick up as much heat.

I had this problem with a engine on the dyno that would constantly overheat no matter how many extra water pumps we added :rolleyes: In the end we realised that the thermostat had been removed and the water was just going around the system picking up very little heat - popped a thermostat back in and it cured all the problems. :D

it effects the ballance of flow around all the cyl liners
minis used to boil 3&4 and cool 1&2 with the stat pulled out st did a flow restricter ring to replace the stat to ballance the flow
its the same reason why you dont change the size of the coolent holes in a head gasket (and yes i have seen it done :rolleyes: try it and you will find out )

Progress on this at last - but backwards :mad:

fitted a new stat and it boiled up as before.

replaced the water pump, but when i tried to refill the system from the expansion tank, it simply wouldn't flow into the engine, until i loosened the top hose at the pump end. It then flowed in niceley, i carried on filling till there were no more air bubbles coming from the loose hose then tightened it and manipulated the hoses till there were no bubbles appearing in the expansion bottle.

Ran it up, and guess what, IT EFFING BOILED UP AGAIN!!!!!:mad: :mad: :mad:

I've put a bunch of pictures of it on my blog, please have a look and tell me if you can see something obvious I've done wrong. Really, really fed up with it today.

Remember when you stuffed those paper towels in the lower radiator hose to stop the dripping, did you take them out?

The more I look at your photos, I think you motor is so freaking big it fills the engine compartment and the air can't go through the radiator cause it has nowhere to go.

Yeah there's no blockages. It is a massive motor dimensionally, the 90 degree vee makes it very wide. The photo's don't show it very well, but there is about 10" clearance bewteen the rad and the engine, and there is no bodywork within the wishbone mounts, providing large holes for the hot air to exit.

Your header tank looks lower than the engine, The tank has to be slightly higher other wise the tank becomes just like abit of pipework. No expansion. Think of it like a central heating system.
What temp is your fan starting to come on????