Bi pass pipe

[bmcecosse]

You know very well Richard! We've had these discussions many times - and your sticking valves. For others - The later Metro (and SPi & MPi ) had no bypass pipe - hence the heads with no by-pass stub. Yes - they had a circuit through the heater - and if you leave the Minor heater tap open - it too has a circuit to allow water to circulate. At least that way - the water moves all round the head - and not just a short-circuit round the front part of the head!

[IslipMinor]

Roy,

Yes we have had the discussion many times, and what you propose for the Minor was never adopted by Rover - they neither eliminated the by-pass circuit, nor drilled holes in the thermostat to provide a miniscule by-pass circuit. As already said in earlier responses to this post, the by-pass circuit is there for a purpose, and whilst keeping the Minor heater valve open maintains a flow through the back of the engine, which is highly recommended, it does nothing for the front, which is where local overheating can, and does, also occur - the Metro by-pass addressed this.

The Metro by-pass is from the front of the head, via the sandwich block under the thermostat, through a circuit that cannot be closed, i.e. the Minor heater valve, and runs through 5/8" bore pipes and hoses through the heater permanently and back to the water pump intake. Now that is a by-pass circuit! Flowing much more water than the original little by-pass hose, and far more than the 2 small 'unofficial' holes in the thermostat, which are not an adequate substitute for what Rover did on the Metro after many hours of R & D. The Metro plumbing also gives the same side benefit as you identify of giving a quicker heater performance, as until the thermostat opens, all the water flow is through the heater. Pity the Metro sandwich block pushes the thermostat housing outlet up too high to connect to the top hose inlet to the radiator - would be a perfect solution!!

I accept you have a different opinion, and that it may be OK on standard (ish) engines, but to give the impression that Rover simply removed the by-pass hose, which they did not, could well result in similar problems with local overheating that I and others have experienced by removing the by-pass hose and not creating an adequate alternative flow to the front of the head.

Water circulation around the front of the A-Series has been known as a limitation for a very long time - in the 60's, the BMC Competitions Department themselves would remove the thermostat to ensure maximum flow, but only in conjuction with fitting their 'blanking sleeve' to ensure proper flow around the front of the head, and no short circuits.

It may well be that the problem becomes more apparent with modified or larger (1275) engines, but it shows that the cooling system design was quite close to the limit and should only be changed with care and full knowledge of what was done by BMC/Leyland/Rover during production.

[les]

Thanks for the post Richard, which I read with interest, I've often thought there must be more to it than just being able to blank it off!

[bmcecosse]

There has never been a problem with water flow to the front of the head - there IS a well known problem with poor water circulation at the BACK of the head - which is precisely why high power A series engines are now usually 'dry decked'. Consider a standard engine starting up from cold with the little bypass in place - water short circuits around the front of the head - but what of the back of the head ? It generates just as much heat - yet is very poorly served by the 'by pass'! If anything during warm up - the front of the head is OVERCOOLED - while the back half is overheating! This 'overcooling' at the front keeps the thermostat shut - but the back end is still heating up - because it has much poorer circulation! Eventually the stat opens and flow is restored all around the head/block. Competition engines almost always have a heater element (as an additional rad if no heater in the car) in the circuit - to allow hot water to escape from the back of the head. Blocking off the bypass helps all this - by allowing the engine to heat up more evenly - and some water flows from the back of the head - through the heater - and back to the pump - then all through the head from front to back cooling gently as it flows - and out to the heater again. This is a much more even 'warming up' process - I suggest! As soon as any worthwhile heat is generated in the engine - the thermostat starts to open - and water then circulates throughout as normal. Certainly the front of the head never overheats. The Mini lads often block the bypass - to get decent/fast heater action - and to eliminate a possible source of cooling system failure. Those who worry - drill some holes in the stat rim to give a little circulation - I ran my 1340 very nicely with NO holes in the rim - the heater worked almost immediately and gave fantastic output - and not the slightest problem with the engine!
Basically - Rover did the mod to get the better heater action, realising the bypass was a non-sense - and they took the heater feed from the front of the engine to get the best possible flow from the pump - but they didn't really consider that they were simply overcooling the front end and overheating the back end of the engine!
If you consider all the engine failures/roadside breakdowns/missed appointments/burned dinners (and possibly even accidents) over all the years the A series has been used - caused by the failure of that little hose - it has a LOT to answer for!

[Stig]

I think I'll try to get hold of a 92 degree thermostat instead for the winter (it's an 88 now). It's easier to change that than mess about with the bypass hose to get a better heater. Anyone know where to get one? I just looked at BM and ESM and no joy.

[IslipMinor]

Certainly the front of the head never overheats.

That is not my experience. During the time (about 2 years) with the by-pass hose removed and no alternative flow path other than 2 small holes in the thermostat, after about 1/2 to 1 mile from cold I would sometimes watch the temperature gauge (capillary) climb rapidly up to around 195°F, then drop back as the 82°C (180°F) thermostat opened - it has the bulb in the standard 'side of head' position. As the temperature climbed I would often get a fairly predictable misfire and clouds of white smoke for a few seconds, as the No.1 exhaust valve nipped.

During the same period the No. 1 plug burnt out (NGK BP7ES) and the No. 1 exhaust valve burnt out (on separate occasions), showing clear signs of 'yellow metal' pick-up on the stem. There were no signs of pick-up on any of the other valves. The same misfire would happen occasionally with the engine under load when warm as well. It was then that I decided to restore the standard by-pass and as if by magic no rapid temperature climb on warm-up!

On the other hand yes, the heater did warm up much quicker without the by-pass in place - can't have everything!

Basic cause? A combination of local overheating and maybe bronze guides that were very very slightly undersize? After replacing the by-pass I would have said the problem had gone away completely, except that very very occasionally on track days, such as at Goodwood a few weeks ago, when I had a single instance of misfire under full load down the Lavant straight - no, I was not looking at the temperature gauge at the time! It rarely goes much over 175°F during any running conditions, except in traffic of course, when it goes up to around 195°F, before the electric fan cuts in to hold it around 190°F. So no general temperature control problems at all, just a tad too much in certain places.

The rear of the head should definitely have a permanent flow, so always leave the heater feed open. It has a Mini heater core and 5/8" hoses to and from it, so lots of flow there.

All this says to me is that for at least a modified 1380, in a Minor, the cooling system flows become a bit strained without a well flowing by-pass in place - it will be staying on ours. Changing the by-pass hose on a Minor every few years is very straightforward - the same thing cannot be said on a Mini. Also on a Mini the cooling characteristics are quite different, with the engine being transversely mounted with no radiator in the air flow from the front of car and so getting a lot more direct air cooling to the whole engine. The 'S' was known to overheat in traffic, but probably more to do with radiator capacity than anything else.

Different views, different experiences - it's what makes life and this BBS so interesting!

[katy]

IMHO, if a valve from a Ford Ka, as described in:
http://www.mmoc.org.uk/viewtopic.php?f= ... Ka#p340237
was to be used in the heater line, with it's built in bypass, that would provide circulation at the rear of the head all the time.

[MarkyB]

Just a random thought about this obviously hotly disputed issue.

Heat is being generated in the combustion chambers.

Water needs to circulate to even this out and ultimately cool it down.

The front of the head and the thermostat get cooled by the air coming through the radiator.


Without any experience of thrashing tuned Minors, my gut feeling is that the reason for dumping the bypass hose may have been taken by accountants rather than engineers.

4 less components, faster build time, one less bloke on the assembly line?
What's not to like if you are an accountant?