Coolant bypass hose

[pandaman]

Evening All
Can the coolant bypass hose be replaced without removing the cylinder head, or is there any tricks to do this job
Regards Pandaman

[GavinL]

You can get 'concertina' hoses that you can fit without removing anything, but they are very fiddly and really only intended as a ' get you home' measure. We did it by removing the radiator and water pump, took about an hour.

[liammonty]

It depends what type of hose is fitted - if it's the concertina type, then yes, you can replace it without taking off the head. However, if it's got a piece of normal hose, then you can't get it off easily without removing the head or water pump. The thing is, even if you did manage to, the concertina ones that you can fit in situ aren't much good, and it's generally advised to fit a normal piece of hose, and that does definitely need the head or water pump taking off to do .

Are you in Plymouth, by the way? If so, greetings from Princetown!

[David W.]

And if I plug the holes and don't use a hose??????????
David

[les]

Some water pumps are blanked off, and so are some heads but unless you've got a problem with fitting a hose, would have thought that was the best way forward.

[philthehill]

The by-pass hose is there to allow some circulation of water before the thermostat opens.
As Les says some late water pumps and heads are blanked off but the water circuitry (via the heater) still allows some circulation of engine coolant before the thermostat opens.
Once the thermostat opens the by-pass hose becomes somewhat redundant.
You can block the water pump and head by-pass stubs with rubber caps available from Mini Spares etc.
I would replace the by-pass hose with the solid type.
In my opinion the easiest way is to take the water pump off but you may find that the leak is from a corroded head by-pass stub and if that is the case then you will need to take the head off to replace the stub or blank off the stub.
If you need to replace the head stub make sure that you get a stub with the right thread which is 5/8" UNS (Mini Sport Padiham). There are stubs being supplied with 5/8" UNF threads which is the wrong thread and will not fit.
http://www.minispares.com/product/Class ... ssic/water pump.aspx|Back to search
http://www.moss-europe.co.uk/hose-bypas ... soc=136577
https://www.minisport.com/12a2075-cylin ... escription
http://www.morrisminorspares.net/shop_item.php?ID=1759

[IslipMinor]

A real potential can of worms this one!

Yes, the later water systems eliminated the by-pass hose between the water pump and head, but did NOT eliminate the by-pass system itself. The by-pass system changed from a by-pass between the head and water pump, to a sandwich plate that fits between the head and the thermostat housing, to allowing a permanent flow through the front of the head.

There have been many suggestions to simply cap off the water pump and head, to make the engine 'warm up faster' - it may do, make only because there is no proper water flow around the head!

I tried it, and had very serious problems with local overheating around No. 1 cylinder, and ended up with a burnt out No. 1 exhaust valve, so reverted to the standard by-pass hose, and no more problems for ~8 years now.

With a standard (ish) engine you may get away with blocking off and eliminating the by-pass system, but I would not advise doing it.

[philthehill]

Richard
And resulting in a sticking valve in the front valve guide if I remember correctly.
One suggestion to overcome the lack of by-pass and allow some form of coolant circulation was to drill a series of small holes in the rim of the thermostat to allow water to flow whilst the engine warmed up.
I would also advise that the by-pass hose is retained unless you have incorporated alternative means of circulating the coolant around the engine/cylinder head.
Below is a photo of a typical sandwich plate of the type mentioned in the above post:-
To reiterate my post above regarding the coolant flow system on those 'A' Series that do not have a by-pass hose.
For example the 1.3 'A' Series engine Maestro:- When the engine is cold the thermostat remains closed and the coolant circulates only through the sandwich plate and heater via the heated inlet manifold and back to the pump inlet hose. That circuitry provides the same function as the by-pass hose. When the thermostat opens the coolant additionally circulates past the thermostat to the top hose.
The heater valve of the Maestro and similar does not fully close and remains open enough to allow the coolant to circulate without heating up the heater core.

Phil

[les]

I remember the sandwich plate from owning an allegro. It also had an expansion tank, I presume that doesn't necessarily have to accompany this plate?

[IslipMinor]

And resulting in a sticking valve in the front valve guide if I remember correctly.

Phil,
Yes it did. The sticking valve problem, i.e. misfire, manifested itself during the warm-up phase sometimes, and also very occasional under load when hot. Eventually No. 1 exhaust valve burnt out and on inspection you could see a very slight witness of 'yellow metal' glinting on the valve stem, which confirmed my suspicions about localised overheating at the front of the head.

As a note, there were no valve stem seals on the exhaust valves either at that time or since.

Replaced the valve AND the refitted the by-pass hose, and the rest is history, thank goodness!

[philthehill]

If after reading these posts and you have a 940 head without a by-pass facility which results in concerns about localised overheating at the front of the head the sandwich plate can be utilised. By fitting a by-pass stub screwed into the sandwich plate outlet and using a piece of shaped 1/2" heater hose connect the stub on the sandwich plate to the stub on the water pump.
By doing the above the by-pass hose function is replicated.
The only down side is that the Minor thermostat housing will sit 25mm higher than normal but I am certain that difference can be overcome.

[MikeNash]

Re Dave W 's query, I plugged the holes in the head and water-pump and have run my standard 1098 Trav for some years that way without trouble. Until recently it had 89C thermostat (now currently 82C). I drive it briskly cruising around 60mph (true) but of course, have water passing through the heater at all times. So my advice is that it can be done safely IF you keep the heater in the circuit. (My old cylinder type heater causes no problem in summer if the fan's not running.)
Regarding Mr Islip Minor's comments, aren't they applicable to a modified engine? That's a quite different kettle of fish!
Regards, MikeN.

[pandaman]

Evening All
Thanks for all the replies to my problem, on looking thro E.S.M. spares there is blue silicone pipes, would this be easier to fit.
Yes Liammonty I live in Plymouth and I if you tell me your car registration I will look out for you at local rallies and are you a member of any local clubs.
Regards Pandaman

[philthehill]

http://www.morrisminorspares.com/coolin ... ps-p829665

It may (???) be easier to fit than a straight hose without taking off either the water pump or cylinder head but I would still fit a straight hose.
http://www.minispares.com/product/Class ... sic/bypass hose.aspx|Back to search

[IslipMinor]

I did say this one is a can of worms!

We have always run the 1380 with an open feed through the heater, but the problem we had was at the other end of the engine. The original design never was without a bypass at the front of the engine, either the original bypass hose, or later sandwich.

A modified engine will always expose the weaknesses of the original design, but the original design was for the 28 hp 803cc A-Series, and that had the bypass hose.

Yes, you may well 'get away' with it, especially with a standard(ish) engine, but what are the actual benefits from doing so?

[philthehill]

The one and only benefit of removing the by-pass facility is that it is one less place to leak coolant and because it is out of sight out of mind so to speak tends to get forgotten about until it leaks.
Vizard gives no benefit for removing the by-pass facility other than that above. He quotes that two 1/4" holes should be drilled in the thermostat rim to allow some circulation of water before the main body/valve of the thermostat opens.
Vizard is most insistent that proper circulation of the coolant around the head takes place so as to alleviate localised heat spots.
The quality of the by-pass hose should always be improved if the radiator pressure is increased.

[paul 300358]

I fitted a 940 head in the summer which has a bypass plug fitted into the head, so I plugged the pump bypass and drilled a couple of holes into the thermostat. This has been fine all summer as the thermostat opens shortly after starting but I am now finding that the heater fails to get properly hot on cold mornings, this appears to be due to the reduced flow as the thermostat remains closed.
The head will be removed, the plug impact driven or drilled out and a bypass fitted when the weather warms up.

[RobThomas]

If it is a later 1275 head then it might be a good idea to add a stub pipe with a more 'normal' thread in it (Metric or even 5/8 UNF?) so it is easier to source a spare one. Someone is selling stubs incorrectly cut for 5/8 UNF so maybe that would be easier?

[philthehill]

Rob
The correct bypass stub is readily available from either Mini Sport, Padiham or Bull Motif.
The thread is already 5/8" (UNS) so fitting a 5/8" UNF threaded stub would not be possible without say putting a UNF helicoil insert in the hole.

[philthehill]

Duplicate post deleted.