I'm trying to figure out your system. I take it the water is pushed through the heads/block by the water pump to the water rail at the back and then down the pipe in the centre back to the rad. I see the pipe is connected to the pump but I assume this is straight through the pump body to the rad.

Correct me please if I'm being thick but I notice on my tintops (both Zetecs) that the hose coming off the thermostat goes to the top hose on the rad and the pump is fed from the bottom hose. Yours appears to be the other way round.

I've been wondering about the tank, the water level is higher than the top of the heads, albeit marginally. I was wondering if raising it some more would give a head of water above the engine which may help?

The fan isn't coming on as I'm not getting any waterflow through the rad as the (NEW) stat is apparently remaining closed.

the pump draws water from the block, and pushes it through 2 external pipes in the vee between the heads to the rear water rail where it flows back into the rear of the heads and round again. The rail also has 2 ports for the donor's heater matrix. The return from the matrix was a Y-pipe witht he expansion bottle on one end, I have attached the expansion bottle directly to this port and blanked the other.

At the front, the pipes from the pump are arranged as per the donor, with the thermostat side going to the bottom of the rad.

Check that you have flow returning to header tank otherwise you will have curculaition problems and it will boil.

The Ginetta I have stripped to make a decent car from (Roadster)has a feed to bottom hose from lowest part of header and returns to top of header from top hose.

What do you mean? My header tank has only one pipe, rather than an inlet and outlet.

Usually a cooling system feeds water to the bottom hose from the base of the tank and returns through a pipe in the top hose to the header tank that is again usually seperate to the rad.

Beemers have a vent in the rad that must be bled otherwise you get problems with airlocks and overheating.

I have not checked the zetec from the Ginetta donor but suspect it has no stat in the back of the head but it used to run at about 70/75 deg at race speed and no more.

In my years as a mechanic I've done more than my fair share of Rover head gaskets and changed the stat and put two small holes in them to allow the water to flow easier and stop airlocks everytime I did one,this may help.

I looked at your pics,if that hose at the rear of the header is meant to be conected to a water rail somewhere that is your problem as you have no flow return.
Alternatively get a VW/Audi tank and fit a tee in the top hose somwhere and feed it to the top of the tank,use the lower to feed as normal in you blog pics.

here's a few diagrams from the donor, provided from the bmw parts catalogue, hopefully this will help.

overview showing pump, rad and pipes. What isn't shown are the 2 aluminium pipes which run from the back of the pump to the rear water rail. These are shown in the second drawing, marked 4 and 6.



detail of the rear water rail. the port near bolt marked 3, is the one I have blocked up. The expansion tank is connected to the port marked 1.



and the original setup of the expansion/header tank.

the rad is lower than the pump, i don't seem to have any air in it. unfortuatelt the rad is of unknown origin, i bought it at stoneleight last year, as it was the exact size i needed and it was only a tenner. it doesn't have a bleed screw.

the stat has a small steel ball fitted loosely in a hole at the top of the stat, i'm guessing it's air bleed device, but it wouldn't be difficult to pull the stat out and drill it, might try that, thanks.

i think this is the same problem i had with my Saab engine. i blocked off the heater circuit and it kept doing the same thing. on some engines the heater circuit has to have a constant flow or it overheats before the stat opens. unblock 3 and either take it to the top of the header tank or splice it into the top rad hose.

a good tell tell sign of the system flowing properly is that you should see water returning to the header tank through the top pipe. if that is not happening then there is something wrong.