Well, not mine but you know what I mean I have it lying on the bench at the moment and noticed that there is no hole in it at all but I seem to remember that they used to have a hole with a little float thing in them that acted as a non return valve. I have heard of people covering these with holes and am wondering what the score is here. I'm keeping the system standard and have removed the blanking plate that was in the engine when I got it. The cooling system holds a fairly impressive 8.5 litres so I think that keeping the stat might be a good idea

Are we talking K or A series here?

Assuming we're talking A-Series.

They are usually drilled when someone fits a Metro engine or head and so lose the bypass hose. You need a path for some coolant to flow before the thermostat opens.

In a standard Mini there are two paths - one is through the heater matrix however the flow through the heater matrix can be stopped by closing the heater tap so they had to add the bypass hose. In a Metro the heater matrix is in the engine bay rather than inside the car and so there was no need to stop the flow through it to keep the interior cool so they could ditch the bypass hose as the coolant could always flow through the matrix.

So in answer to the question - so long as you maintain a coolant path that can't be blocked before the stat opens no you don't have to drill it.

It was always my understanding that the single hole with the float in was to aid in bleeding the system as air would pass through the hole untilcoolant reached it and then the float would close it off.

Iain

That's right.

The hole in the stat was to bleed out air. It had nothing to do with water flow.

That's very interesting Iain. It's an A+ and I've been dithering a bit about the heater, which is the usual Mini item. I was aware that there was an issue about shutting off the flow to the heater although I have fitted a manual valve just at the heater itself. I had thought that maybe I could keep the valve open until the engine warmed up and then close it but that doesn't seem very satisfactory. From what you're saying, I could drill a few holes in the stat just to maintain a bit of circulation around the engine and close the heater valve - is that correct.

I stand corrected regarding the purpose of the little float as well. It's a marvellous educational tool this forum, innit?

Yes that's correct,3 or 4 small holes is ok. Think it tells you about in Vizards A series book.

On the first startup on a new-filled engine air can be traped under the termostat, so it will be part or fully dry, thus its operation will be much slower => You will boil your engine.

When Leyland/BMC/Rover made the Allegro they decided to blank off the small by-pass hose on the A series motor and used the heater circuit as the by-pass system instead. They blanked off the cylinder head takeoff, fitted a sandwich plate under the stat and tapped into the bottom rad hose. They deleted the valve in the plumbing so that hot water flowed constantly through the heater and mixed hot and cold air to control the temperature.

You have to have some water flow even with the stat closed or the impeller is pushing against a closed system so you need some sort of by-pass. If you run a water heated manifold too you also need a constant water flow through that too.

I plumbed my GTM like this.



The by-pass system flowed from the sandwich plate, through the car heater, back to the manifold and into the water pump through the 'T' in the bottom rad hose.

The main system flowed, as normal, through the stat to the rad and back to the pump through the bottom hose.

I used a filler T piece at the highest point in the system to avoid air locks.

That will work and as stated is pretty much the same as the Allegro or Metro ran but again the heater will always be warm. Wasn't an issue on the Allegro or Metro as the matrix is on the engine side of the bulkhead so you get little or no heat in the passenger compartment until you actually switch a fan on and start drawing air through it.

Te other advantage of this system is that the heater matrix is much less prone to silting up during the summer months when on a Mini system you would have the tap closed and never see any flow through the matrix.

Putting a tap in there and just not closing it until the engine is warm is fine but you must remember to open it as part of the startup routine so it's a bit of a faff.

I seem to remember something about a three way valve from another car which would allow you to close off the heater and feed that flow to a T-piece after the matrix. Effectively this would just bypass the matrix but keep a flow going. Micra seems to ring a bell where this is concerned.

I've also wondered in the past about using longer studs and two sandwich plates - one for the heater and one just to run a length of hose to the bottom hose to replace the bypass. Possibly a simpler alternative is to run the Mini tap on the far end of the cylinder head to the stat feeding the matrix and the return from the matrix going to a T in the bottom hose. You then also run a sandwich plate below the stat which just has a short length of hose that also goes to the bottom hose and maintains a bypass route if you leave the heater tap closed when starting a cold engine. One possible problem with this setup is that the coolant will follow the path of least resistance and flow from the sandwich through the short hose rather than going through the matrix so the heater will never get very warm - the original Mini system gets around this because the bypass is a quite narrow pipe and so more restrictive than the matrix.

My GTM runs the coolant through the matrix all the time and it can get a bit hot and sticky in the cabin on warm days whereas my Mini doesn't run a heater at all so the pipes are just connected in the engine bay to provide the bypass (late SPi engine with no bypass in the head). I do want to address it on both but it's way down the priority list at the moment so someone else can be the pioneer.

Iain

Great stuff, gents - thanks very much for our input. I was looking for a 3 way valve but didn't come up with anything and anything else I could think of involved too many valves etc and took up far too much room. I don't like having any more joins than I can help, either. So.... for the moment, I've drilled the thermostat and that will do meantime until I get everything else sorted out. I'll come back to it another day in light of all the info above (brilliant graphics, gtmdriver )

My priority at the mo' is to get the damned thing running - it starts, runs for a few secs and then stops I've checked out everything I can think of, stripped the carb twice, changed the fuel pump etc etc but no luck. I think I need a witch doctor to exorcise the bluddy thing

I've been wondering about this aswell... I have an A+ Metro engine and the heater is constantly hot with no heater control. I can't remember what sort of thermostat I put in when I assembled the engine but it was new and un drilled.
When running the engine warms up quickly and I get good heat out of the heater, but the rad barely seems to get warm at all- after prolonged idling the pipe after the thermostat starts to warm up a bit but up front nothing much. I have a small hose on the bottom of the rad which I am using to try to bleed the system and I have had fairly warm water coming out of there in the past so I guess the system sort of works.
I suspect it has some air locks in there, but would drilling a few holes in the thermostat help...?

Ed

By the way mine is plumbed up exactly the same as GTM Drivers diagram above, but without the elctric pump.

Ed

All Thermostats in past used to come with hole and “wiggle valve” that was always put at the top to help bleed air out of the system. In my Imp powered Davrian, I always drill a hole through the Thermostat, this due to the poor design of the water pump that cavities the water, so it is important to remove this air from the engine. So I now tend to drill every thermostat regardless of what car they are going in, the bit of flow you get in very small and worst case it may take longer for the engine to warm up.