no bypass - A+ engine

[LaughingBoy]

Can anyone offer some advice? I am concerned about the cooling system on my A+ engine. I have no bypass hose (the water pump bypass is blocked off) and I do not have any special feed to the heater from under the thermostat (as in the Metro?).

My engine has a heater tap at the back of the head which runs to the heater and then returns via the inlet manifold to the bottom hose just by the pump. So I guess this acts as a bypass when the thermostat is closed, with water happily flowing through the head. But when the thermostat opens, will the system function correctly with coolant correctly flowing through the head?

Any help greatly appreciated ...

[bmcecosse]

Of course it will! You have the ideal system for a quick warm up and best heater action. I always keep the water flowing through the heater - but it's not really necessary -and I don't 'heat' the inlet manifold since I am looking for best performance.

[LaughingBoy]

OK thanks for that. I also leave the tap open in summer but sometimes when it's very hot would like to be able to turn it off. If I did turn it off then presumably I'd no longer have coolant flowing round the engine (until the thermostat opens) and would have to drill holes in the thermostat rim to allow a small amount of flow durin engine warm-up ??

[bmcecosse]

You can drill a couple of 1/8" holes if you wish....but then you will lose the 'quick heater' effect. Perhaps do that in your 'summer' 74 deg stat, but not in the 'winter' 89 degree stat.

[philthehill]

I cannot see why there should be a problem/concern with shutting off the water flow through the heater. When you turn the tap off either by the tap on the back of the head or by the lever on the heater control inside the car the water stops flowing through the heater and that is normal whether it be Minor 948cc or 1275cc with or without bypass. The water still flows/circulates around the block, temp is controlled by the thermostat and the engine does not overheat. All perfectly normal!

[bmcecosse]

I tend to agree Phil - but when the stat is closed -with no bypass - there will be NO worthwhile circulation. A couple of 1/8" holes makes sure there is some flow around - until the stat starts to open and then everything is as normal.

[philthehill]

The above is normal; therefore BMC/BL saw no need to drill holes in the thermostat or install any other bypass system to aid circulation around the block until the thermostat opened.
A solution to a problem that is not there is being suggested!

[bmcecosse]

Not so Phil - the no-rubber -pipe bypass engines had an alternative bypass arrangement via the sandwich plate under the thermostat.

[philthehill]

Not sure that I totally agree with you!
For example:- the 1300cc Maestro which has the sandwich plate and NO bypass hose.
The normal heater take off point at the back of the head is blanked off so the sandwich plate is used as one of the heater connections. Quote from the Haynes manual:- "on the 1.3 model the coolant first passes through the water jacket on the inlet manifold before returning to the pump inlet manifold (unquote - which is below the thermostat). When the engine is cold the thermostat remains closed and the coolant circulates only through the engine and heater. When the coolant reaches a predetermined level the thermostat opens and the coolant passes through the top hose to the radiator" Therefore the initial coolant circulation is to the inlet manifold only.
There are NO other pipes/fittings identified to enable water to by pass the thermostat.
So the coolant flow can be as I described above and that how it works on the Maestro 1300cc and that is why I have no concerns regarding the water flow as described in the original post when the heater tap is switched off. That does not mean to say that BMC/BL did not subsequently modify the coolant pipework to allow a small percentage of water to bypass the thermostat but that is a different story!
I have attached a photo of the sandwich plate and the only take off is for the heater pipe immediately below the thermostat.[frame][/frame]

[irmscher]

Electric water pump very cheap job sorted

[philthehill]

Don't know about cheap!
The Davis Craig electric water pump as fitted to my Minor was £144 plus VAT and the thermostatic electronic water pump controller was about half that.
The cheaper version with controller is still £214 plus VAT.
The Bosch booster pump with 19mm inlet/outlet and which can be fitted into the heater pipe circuit is £69.99 plus VAT.
If you know of a source of cheaper electric pumps please tell us!

[bmcecosse]

On these systems the heater flow is never closed off - so there is always some circulation. I really don't believe it matters a jot - but we can be sure Richard will be on soon with his tale of woe which he attributes to having blanked off the bypass on his engine.....

[irmscher]

Phil go on any of the rally forums loads cheap you don't need to buy new

[IslipMinor]

Apologies for the tardy, predictable reply, we have been on holiday for 2 weeks.

All A-Series engines had a by-pass circuit as part of the original design. The first type was the familiar by-pass hose between the cylinder head and the water pump inlet, which allowed water circulation around the block and head at all times. The second type was the sandwich plate that was fitted between the thermostat housing and the cylinder head, and used the heater as part of the by-pass circuit before the thermostat opened.

I really don't believe it matters a jot

I'm sure if it didn't matter, BMC would not have incurred the cost or complication of providing the by-pass circuit.

Fitting the later type head, with no by-pass, on to a Minor block means there is no water flow around the block and head (unless the heater valve is open) until the thermostat opens. Drilling a couple of small holes in the thermostat will allow a small flow, but as has been well documented, this did not work on our 1380, even with the heater valve permanently open, and the local overheating at the front of the engine gave 2 years for misery, cost and No. 1 exhaust valve and plug failure. Reinstating the standard by-pass hose 4-5 years ago solved the problem completely. Maybe on a standard engine it can work, but not for us on a highly modified one.

Competition A-Series engines often run with no thermostat or by-pass, but the lack of a thermostat provides a huge permanent by-pass, so obviously no likely problems!

[bmcecosse]

I'm sure you admitted before Richard that you also fitted a new guide when you refitted the bypass - and my view is that the guide was the problem. and not the bypass. The logic doesn't stack up. Many hundreds of Minis are running around without the bypass -and no one has ever reported your misfire etc... On that basis I am SURE it doesn't matter a jot......

[IslipMinor]

It wasn't just the valve sticking, I had plugs (BP7ES) burning out as well - always on No.1 cylinder. On warm up I could watch the temperature gauge wind round to towards 200°F, the misfire would begin, white smoke pour from the exhaust and then the thermostat would open (82°C), the misfire would stop, no more smoke and normal running temperatures. It would then re-occur if under heavy load sometimes and stop immediately if the throttle was backed off.

It was only when the No.1 exhaust valve burnt out that I found that the problem was the guide nipping the valve stem (yellow sheen on the stem) and causing the misfire. The guides were checked 3 times by the supplier (a very well-known engine builder) and found to be the correct bore size.

Having no by-pass hose, but 2 small holes in the thermostat rim, was the cause of intense local overheating of No.1 cylinder, which forced the guide to expand inwards (constrained by the head from going outwards) and nipping the valve stem. I'm sure there could be other engines where this does not occur, but that does not mean it cannot happen, it did!

To repeat - BMC never removed a by-pass circuit from any A-Series installation. That is good enough for me.

[MarkyB]

this did not work on our 1380,

Does this have any relevance to standard Minors?
Or mildly modified ones for that matter.

[bmcecosse]

My very heavily modified 1340 ran very well indeed with no bypass - and excellent heater within 1/4 mile of the house! Your 82 degree stat Richard would ALWAYS keep the engine at ~ 200 degree F....so I can't see the argument. DID you have holes in the stat? I suggest the sticking valve wouldn't have done the plug any good either....

[MarkyB]

What material were your valve guides Roy?

[bmcecosse]

Just steel Marky - genuine Cooper S head air flowed with large inlets and exhaust, and a 544 camshaft, but no silly 'high ratio' rockers..... And yes - I know Cooper S heads had special phosphor bronze guides as standard, but I couldn't afford them......