I'm struggling to get my thermostat housing off at the 'mo due to the original bolts being seized (I'm pretty sure my 'stat is duff) Do I really need the lower of the 2 parts or can I just put the top bit back a la Mini?

Or would I need the bypass hose to the pump if this was the case?

Also, what are your thoughts on opeing up the heater takeoff at the other end of the head (Mine is still blanked) and if I did, where would it be best to route it to?

ta

You do need a bypass of some sort until the stat opens. Obviously in the Mini this is done with the silly little hose. In the Metro it's done with the heater matrix as the matrix isn't actually in the car so as long as you can block the air-flow you don't get too hot in the summer. On my Mini I've used a Metro bottom hose which gives me two "outlets" in the bottom hose. One is connected to an expansion tank and the other via the heater matrix to the outlet at the far end of the head (a straight outlet and not a tap as I need the flow so never want it to be closed). I don't run a sandwich plate or bypass hose. In the warmer parts of the year I disconnect the matrix (flush it and drain it too) and "short" the two ends together in the engine bay to keep the heat out of the interior. This might be a bit much messing around for some people. In theory if I ran a tap I could simply close it once the stat opened to keep the matrix cool but I'd have to remember to open the tap again when I next started the engine from cold.
I have considered running a sandwich-plate too and connecting it to the pipe that goes to the expansion bottle at the moment. This would effectively give me two parallel bypass paths. An inline tap in each would allow me to select whether the bypass went through the matrix or the straight tube so 30 seconds under the bonnet could give me a warm or cold matrix depending on the weather.

The things I don't like about this are that I'd loose the expansion bottle and I don't like running without flow via the heater tap outlet as it can make for hotspots in at the far end of the head (I know the Metros ran like that for years but the engine was designed a long time before the Metro came along.....).

Some people also do away with the bypass by drilling a number of holes in the stat flange - in some cases people will argue that they've done it and it's worked for years and in some cases people can't get it to work at all. I don't like the idea so I've never tried it.

Iain

Iain,

Thanks for that.

One thing i'm looking to avoid is yet another pipe or pipes running down the centre tunnel as it's getting very congested in there, so I was hoping to tap off the main cooling pipes at the front for the heater.

Has anyone got that diag of how water flows through the a-series to hand?

Basically you need to arrange for the coolant to get from the top of the engine to the water pump. I'd be concerned about a couple of points in Ken's diagram. Coolant will always follow the path of least resistance which generally means the biggest hose. The heater matrix is in parallel with the radiator and the main hoses so I'd expect to see very little flow through it as it's much easier for the coolant to flow through the main hoses and the rad. The same goes for the hose from the heater tap to the top hose with the additional problem that both ends of it are effectively connected to the same thing so there is likely to be very little pressure differential to drive any flow.

Iain

The reason for the heater circuit being in red, is it isn't fitted yet. So I can't say how it works. I'm not too worried about the heat part, more just as a demister for the screen.



It used to be common practice, in my Mini days, to do this when you removed the heater, it's better than blocking off the outlet. As the head can develop hot spots. My guess there is enough flow to do the job.

I guess you could hook up a small heater matrix in the engine bay and then plumb it back to the bottom hose, as additional cooling.

I had the exact same system to my race mini as shown in Ken's diagram minus the heater of course, however I had twin radiators and did not have the header tank as mine was a standard style mini radiator. I had a 'Y' seperating the sat hose and the old heater take off, this line went to the 1st radiator which then flowed to the 2nd radiator then back to the pump, I could run all day in 30+ deg heat with the engine staying around 165-170 deg F. I however had bored out the heater outlet to it maximum size to increase the flow capabilities. I don't have a photo on my computer at the mo but I check my records at home and try and upload something. I have ditched the heater in my coupe and have installed an electric one from CBS to do the window demisting. The cockpit in a coupe is so small that a heater seems a waste of effort, space and of course weight.

http://www.cbsonline.co.uk/electric-demist-heater--demst-309-p.asp

One of these ?

I'm not advocating blocking off the heater tap outlet but I think it should be connected to the "bottom" hose rather than the top one i.e. to the low pressure side of the rad. The thermostat will give a restriction in flow between the head and the stat housing/top hose which isn't present in the smaller pipe from the heater outlet so thinking about it a little more you probably will see a flow from there to the top hose which varies as the stat opens and closes as the hose side of the stat will be at a lower pressure than the head. You'd still see more flow if that pipe was connected to the other side of the radiator though.

On a different note and for a heater idea - why run a matrix? It would be possible to run an air-duct from the heater intake to immediately behind the radiator. You would pick up warm air and I can't see it cooling off that much between there and the interior. You'd want some sort of funnel pressed against the rear of the radiator and you'd need to make a reasonable seal between the duct and the heater intake so that it draws the air that's passed through the rad.

Iain

Then you are pulling hot water into the engine, as it will bypass the radiator and never get cooled.

Yes Ken one of those, it seems to work well as the Coupe is so small, I haven't had it working in a real life situation yet but I can't see why it wouldn't work. I don't intend to use my Coupe as a daily driverr more a Sunday fun car so I would be very surprised if it ever gets used.

This is the circuit I am using.



The two circuits are basically separate.

The main cooling circuit flows from the thermostat to the radiator and back to the water pump via 28mm copper pipes and silicone hoses.

The bypass circuit flows from the sandwich plate through the heater and the inlet manifold to the water pump via 15mm copper pipes and silicone hoses. The filler cap is in this circuit at the highest point. The heater works fine.

As with all the later A and A+ series engines there is no bypass hose and no take off by No. 4 cylinder. In fact on later cylinder heads the 'heater' take off is not even drilled. This is exactly the same situation as occurred on the old heads when you closed the heater tap anyway.

The Craig Davies electric water pump was fitted at the same time as the Laminova Oil/Water heat exchanger. I was worried that the extra heat input from the oil cooler may be too much for the cooling circuit.

In fact the system works so well in practice that the pump never switches on whilst driving. It only switches on if the engine is left idling in traffic or if the engine is turned off shortly after a hard run, when the heat soak triggers the pump.

I use to run one of those Craig & Davies pumps on my race mini as the std mini pumps would cavitate at about 5500-6000 RPM, have you put a speed controller on it as we found that they spin far to fast for a mini's small cooling system therefore speeding the flow of the water through the radiators and not allowing enough time to cool the water. I didn't use the mechanical one at all and fabricated a plate to suit just the input from the electric pump. They are fantastic at cooling and also allow the engine to cool down once stopped. I made a speed controller out of an 240v electric heater resistor coil effectively dropping the voltage to the pump to approximatley 6v.

Another thing is that if you are worried about different pressures in the top hoses i.e main vs heater then just remove the thermostate and replace it with a blanking plate. It will just take a little longer to heat up but nothing major. An easy way to do this is by cutting the centre out of the thermostate, don't remove the thermostate all together as you will create cavitation in the housing.

I've kept the innards of my standard water pump and I don't run a speed controller but I do have a thermostatic switch so that the pump can't switch on untill after the thermostat has opened. If it fired up with the stat closed it would be pumping against a closed system and could do itself damage.

It's not intended to be cooled. It's intended to allow coolant to circulate around the block before the stat opens to avoid hot-spots and promote an even warm-up. Follow the red line on gtmdriver's diagram. That's almost precisely the system I run on the Mini but I've connected the heater circuit to the other end of the head where the tap would go on a Mini and I don't run a sandwich plate.

On my Mini it's a late Cooper head so both the heater take-off and the temp sender hole were not drilled. The holes for the bolts that hold the tap in were tapped so it was just a case of drilling the centre hole. I then made a take-off from a piece of plate shaped and drilled to match the gasket with a short length of copper braised into the centre hole.

Iain