by-pass hose

[ampwhu]

can we live without it? what does it actually do?

[Jefftav]

You can do a way with the by pass hose but you will have to blank off the outlets from the water pump and thermostat housing. You can buy a Marina water pump without the outlet.

I ran my 1098 minor like this for long enough with no problems

[ampwhu]

i'm thinking of screwing a temp sender into the bypass stud in the head.

[bmcecosse]

After many many years of untold misery caused by that wretched hose (just think of the appointments missed/accidents caused and money wasted with roasted engines........) MG Rover finally saw the light and eliminated the ghastly bypass hose. Just blank off the holes - or even just fill the hose with silicon sealer. Then drill 1 x 1/8" hole in the rim of the thermostat to allow a small amount of water to circulate (actually - if there is a little bobble valve in the thermostat - just rip that out instead of drilling!) - and your engine will warm up much more quickly - the heater will start working almost immediately - and the heater will work much better too! It's a win-win-win situation. To run a temp gauge - use a thermostat cover with the sender take off tapping in it.

[ampwhu]

After many many years of untold misery caused by that wretched hose (just think of the appointments missed/accidents caused and money wasted with roasted engines........) MG Rover finally saw the light and eliminated the ghastly bypass hose. Just blank off the holes - or even just fill the hose with silicon sealer. Then drill 1 x 1/8" hole in the rim of the thermostat to allow a small amount of water to circulate (actually - if there is a little bobble valve in the thermostat - just rip that out instead of drilling!) - and your engine will warm up much more quickly - the heater will start working almost immediately - and the heater will work much better too! It's a win-win-win situation. To run a temp gauge - use a thermostat cover with the sender take off tapping in it.

i have a thermo housing with a threaded hole under the hose connection. seems to me that if i put a thermo in, then the sensor pocket wouldn't fit as the thermo would be in the way. hence the reason why i could just screw it in where the bypass stud was. then just blank off the waterpump.

make sense?

[bmcecosse]

It should go in there ok - that's what the tapping in the cover is for. Yes - IF and that's a BIG IF - you can get the stub out of the head - it is the same thread I believe as the thermo sensor. And there's not much room to work there - so head off job I suspect.

[ampwhu]

It should go in there ok - that's what the tapping in the cover is for. Yes - IF and that's a BIG IF - you can get the stub out of the head - it is the same thread I believe as the thermo sensor. And there's not much room to work there - so head off job I suspect.

heads off and the stud is removed. so if thats the case, i shall look into it.

[bmcecosse]

Oh well! Just need a pump without the stub - and do drill that 1 x 1/8" hole.

[IslipMinor]

MG Rover finally saw the light and eliminated the ghastly bypass hose

Yes, they did eliminate the the head to water pump hose, but they did NOT eliminate the bypass system, just did it differently. Look at the Metro where the thermostat is mounted on top of a housing that is part of the revised bypass system.

It seems that with a standard (ish) engine you can get away without a bypass, but with a well modified engine and bronze guides in an unleaded head, you are very likely to get the No.1 exhaust valve nipping under load, and quite quickly burning out. Been there!!

[bmcecosse]

Pretty sure we 'proved' that can't have been the cause a while back ! A hole in the stat acts as the bypass! And as soon as any temperature develops - the stat opens allowing full flow. So there is no stress on the head or valve guides.
QED

[IslipMinor]

Roy,

As I said, for standardish engines, it may well work OK, but BMC/Rover never followed that route, so I presume they had good reason.

There has certainly been a lot of discussion, but a small hole in the thermostat does not provide anything like the same level of water flow as the original or other Rover by-pass designs do.

I am convinced that eliminating the by-pass was much of the problem I had a few years ago during the initial warm up phase, before the stat (82°C) opened. After about 1/2 - 1 mile, I would see the temperature start climbing (my bulb is in the standard 'side of head' postion), a misfire, clouds of white smoke from the exhaust, followed by a levelling off in temperature as the stat opened, and no more smoke or misfire. The problem could sometimes reappear with a sudden opening of the throttle, from a light cruising level, when the rapid heat build-up in the combustion chamber and valves could not be carried away quickly enough by water flow through the partially opened stat (including the little hole in it). Again, I would see a temperature increase, misfire and smoke, and then the stat would fully open and back to normal again. This all took place over a 20/30 second timespan.

Another factor in all of this is that unleaded fuel burns slower and hotter than the old unleaded, so contributes to heat build up. The A-Series for ever has been known to have slightly limited cooling capability - look at the standard requirements from Special Tuning - leave the heater valve open, and if removing the stat, their 'blanking sleeve' must be used instead. This didn't truly 'blank' anything, it made sure that the water circulated around the head properly, by preventing it taking a short circuit though the empty stat hole! ST also said that the by-pass could be removed; not really surprising as there was a huge permanently open hole where the stat used to be!

Going back to the standard 'head to pump' bypass has elminated the problem on our 1380, as it provides a permanent circulation around the front of the head to accomodate any heat build-up that occurs before the stat has time to react (it's not a switch, it takes a finite amount time to open, and it was during this opening time that many of the problems I had occurred). Without the by-pass in place the cooling system relies on the opening speed of the stat to increase the water flow around the front of the head, which does not happen quickly enough to prevent a local hotpsot around No. 1 cylinder and overheated valve stem, which then can be 'nipped' by the bronze guide. With the original or other by-pass system in place there is more reserve in the system. A standard engine may not require this reserve, so all 'appears' to be well. Not good engineering in my book.

If people want to remove the bypass system completely, they should be aware that it is not what BMC or Rover ever did and I have experienced serious problems on a highly modified engine as a direct result of removing it.

I expect we will disagree about the need for the by-pass, but that does not mean that it is not there for a good reason, or that removing it is risk-free.

[bmcecosse]

I note what you say Richard - and you are obviously convinced! But many Minis run without the bypass -and none have reported anything like this problem. It is of course possible to have many holes in the stat rim - I found 1 to give rapid heater warm-up and good heater performance. I would say - an 82 stat is a bit too high for a performance engine - preferring 74 myself - or no stat - blanking sleeve for my 'race' engines.

[IslipMinor]

Roy,

Would like it all ways round - reliable cooling and a good heater!!! At the moment all looks fine.

[Kevin]

I am convinced that eliminating the by-pass was much of the problem I had a few years ago during the initial warm up phase, before the stat (82°C) opened. After about 1/2 - 1 mile, I would see the temperature start climbing (my bulb is in the standard 'side of head' postion), a misfire, clouds of white smoke from the exhaust, followed by a levelling off in temperature as the stat opened, and no more smoke or misfire. The problem could sometimes reappear with a sudden opening of the throttle, from a light cruising level, when the rapid heat build-up in the combustion chamber and valves could not be carried away quickly enough by water flow through the partially opened stat (including the little hole in it). Again, I would see a temperature increase, misfire and smoke, and then the stat would fully open and back to normal again. This all took place over a 20/30 second timespan.

Well that's got me thinking Richard as I blanked off the bypass and fitted a metro pump without the outlet on my 1275 Midget engine.
Sometimes like yourself and after a similar distance I get an oily smell shortly followed by some smoke for a very short period, it doesn't happen when the car is warm only from a cold start and on cooler day's. I in the end put it down to a split gaiter dripping onto my exhaust system which has now been replaced but I have had it happen a couple of times since so I may restore it if it happens when the weather cools down again and it reappears.

Roy as a matter of interest do you still have a bypass hose fitted to your Traveller.

[bmcecosse]

No - it's blocked off. The 940 head had no tapping - the pump does - so a blocked off hose fills the space! My 1340 Mini engine didn't have one either - although the Mini was swapped for a TR7 3 years ago now.