water pump bypass pipe

[davew1949]

I'm replacing the water pump on Boris and on removal I noticed that the bypass pipe attached to the head under the thermostat housing seems to have corroded and broken off and is now only about 1/2 inch long. I'm a bit worried about renewing everything and then finding this leaks.
I've followed the 2004 link by Fweddy and it seems it is possible, with a bit of luck, to get the old pipe out, but does anyone know where I can get a new pipe from?

Cheers,
Dave

[chrisryder]

Any minor or mini parts supplier should stock them.

I was able to get mine out by welding a T-bar into it. The heat helps to un-seize the thread.
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[bmcecosse]

Good idea - then PLUG it to eliminate the ghastly hose........ http://www.minispares.com/shop/classic/ ... ng.aspx?07

[davew1949]

Well I managed to get it out. Tried the "hammer in a screwdriver" solution, but that unfortunately didn't work for me. It needed lots of chiseling and I finally broke it out with a sharp centre punch working round the outside. Unfortunately the inner thread on the head looks a little bit damaged in one place from the corrosion. I've now got a new pipe which I would like to fit (I hear the recommendation about blocking it off completely, but I know there is some debate so I'll take the original route).

What would be the best compound for sealing the thread do you think? I have ordinary blue gasket goo, some silicon type plumbing compound called LS-X which says it is good for over boiling point temps, or ordinary plumbing compound. Or is there something better?

All thoughts very welcome.
Many Thanks,
Dave

[David53]

I'm curious - if the bypass is so useless why was it included in the original design?

[bmcecosse]

It's only useless when the hose bursts - must have caused more ruined engines/breakdowns/missed appointments - maybe even deaths (car being run in to when stopped at roadside) - then anything else on the Minor over the years. Eventually MG Rover wakened up to the fact and eliminated it. Either follow their method (spacer under the thermostat cover) - or just drill a couple of small holes in the rim of the thermostat - AND keep the heater tap open all year round. As for sealing this - I would wrap well with PTFE tape and keep my fingers crossed.

[MarkyB]

It's only useless when the hose bursts"

If that's the only time, then use straight hose and the heater as intended!

[les]

'burst bypass hose could causes death'---Roy you've gone over the top!!

[bmcecosse]

Sadly - I suspect it's likely - but of course I have no evidence for that. But it is amazing how often cars stopped on the hard shoulder/side of road are run into by other vehicles.

[davew1949]

However, returning from the compelling and enjoyable subject of sudden death, to the somewhat more pedestrian topic of sealing the bypass pipe, I am not really a great fan of PTFE tape. Even when I have used it on domestic water pipes I often have to re-do it several times before the drip finally gets cured. So the idea of using it on this difficult to replace pipe isn't very appealing. I was wondering if anyone had found an ideal gunk of some kind for this type of joint. Not sure if it makes any difference, but the new pipe is brass rather than steel.

Dave

[bmcecosse]

Loctite sell a sealant that you wipe on the thread - supposedly instead of ptfe tape. You could try that - although the tape applied correctly will be fine.

[David53]

I guess my question really is - if the pipe can be blocked off without any effect on the operation of the cooling system, why was it included in the original design? Surely there must be reason it's there?

[IslipMinor]

if the pipe can be blocked off without any effect on the operation of the cooling system, why was it included in the original design?

Two parts to the question and taking the second part first:

It is included to provide effecive circulation around the front of the head and block during the 'warm-up' phase, before the thermostat opens, otherwise there is little circulation around the front of the engine. Removing it has been done on many occasions, and you may get away with it on a standard engine, but on a well modified engine running on unleaded fuel the cooling becomes more marginal and from very bad personal experiences needs the by-pass system in place. Unleaded fuel burns hotter and slower than leaded and the combination of this and restricted front of engine water flow with no by-pass hose, caused all sorts of problems, which disappeared as soon as I restored the by-pass hose.

The development of the A-series engine never simply blocked off the by-pass hose; the design used a different way of achieving the same result and put a sandwich plate between the thermostat housing and the block so that the water can still circulate when the thermostat is closed.

As has been said earlier, it is there for a purpose and I believe should be left as designed. Replacing the hose once every 5 years or so is not particularly onerous and makes sure that the engine cooling is complete, will no possibility of storing up problems for the future.

[David53]

Thanks, I thought the engineers must have had a good reason. Just a question on thermostats - if and when they fail do they stay open or closed? And either way what is the damage that can be caused?

[bmcecosse]

I've only ever seen them fail open. Overcooled engine will sludge the oil - and not give best fuel economy.
I'll just point out again that Richard's valve problem which he attributes to having no bypass hose - is the ONLY known case in the world.........

[MarkyB]

The interesting thing about Richards problem is that reinstating the bypass hose cured it thus proving that the bypass hose does make a difference in that area.
"Overcooled engine will sludge the oil - and not give best fuel economy."
True enough but overcooling won't happen with a working thermostat in place.

[bmcecosse]

The overcooled comment is in respect of a thermostat which has failed open. As I remember - and I'm sure Richard will be along to verify - refitting the bypass was not the only 'change' made at that point. I'm not sure that 'unleaded' valves should be run in bronze guides either........ But in any case - most high power A series engines are run with a blanking sleeve fitted - instead of a stat.

[IslipMinor]

which he attributes to having no bypass hose

Sequence (again) is:

Unleaded conversion + removed by-pass hose at the same time, immediate (<1/2 mile from home on first run) misfire under only very moderate load going uphill. Replaced all the fuel system and tested replacements for distributor and even the coil! Always got very slightly better with each change/test, but the 'misfire under load' never went away. I even bought a 'blanking sleeve' to try without a thermostat, but never fitted it as then No.1 exhaust valve burnt out and close examination showed 'yellowing' on the stem, which was the first indication of the real cause - local overheating and valve pickup between the stem and guide. Rebuilt the head, replaced the by-pass hose and bingo!

What is so difficult in recognising the root cause to the problem!! That was all 3-4 years ago and no more valve problems or misfiring since.

is the ONLY known case in the world

The question is , who's world?

[bmcecosse]

Really - it was just a tight valve/guide that was picking up. I honestly don't believe the missing bypass had anything to do with it - but I appreciate you do. If anything - the limited flow occurs at the other end of the head - and is the reason for the 'dry deck' conversions that some folks carry out.

[les]

To conclusively prove a point the experiment should be repeated and the same results obtained.