26 replies to this topic

[nicklouse]

Ok leaving the A series as they have the bypass hose in most cases lets look at how the cooling/heating system works most do not have a bypass if the heater valve is closed.

 

the MPI does as it has an extra pipe for when the heater valve is closed.  the metro had no heater valve as the heat distribution was done by the flaps and the heater ran hot water though it all the time so that was the bypass.

 

lets look at the Mini A+ motors  they either had the take off on the head or the sandwich below the thermostat and then went to the heater matrix with a valve in the hose to the heater and then returns the bottom hose. no bypass hose. No heat in the cab equals no bypass system.

 

the mini thermostat should have a small hole in the edge with a wiggly thing to do a few things. let air past and also allow some warmer water past to help heat up the thermostat so it can do what it needs to do.

 

also note as hot water is pushed through the block it pulls the cold water out of the head until it warms up.

 

if i have missed something please point it out.

[Readers14]

Good explanation Nick!

[nicklouse]

some further coolant reading I just don't agree about all the extra holes being required in the thermostat.

https://www.calverst...g-how-it-works/

 plus lots more useful infos

[nicklouse]

opps

Edited by nicklouse, 26 October 2018 - 02:12 PM.

[Readers14]

some further coolant reading I just don't agree about all the extra holes being required in the thermostat.
https://www.calverst...g-how-it-works/
 plus lots more useful infos

I’m under the same opinion.
That’s why I want to delete the bypass hose. I already have the sandwich place with outlet to the bottom rad hose. So bypass is not required for me.

[nicklouse]

 

some further coolant reading I just don't agree about all the extra holes being required in the thermostat.
https://www.calverst...g-how-it-works/
 plus lots more useful infos

I’m under the same opinion.
That’s why I want to delete the bypass hose. I already have the sandwich place with outlet to the bottom rad hose. So bypass is not required for me.

 

ahhh that brings about another issue. bottom hose or top hose.

[Readers14]

some further coolant reading I just don't agree about all the extra holes being required in the thermostat.
https://www.calverst...g-how-it-works/
 plus lots more useful infos

I’m under the same opinion.
That’s why I want to delete the bypass hose. I already have the sandwich place with outlet to the bottom rad hose. So bypass is not required for me.

ahhh that brings about another issue. bottom hose or top hose.

Sandwich plate to bottom hose (I think!)

Top hose is only thermostat housing to rad.

[nicklouse]

 

 

 

some further coolant reading I just don't agree about all the extra holes being required in the thermostat.
https://www.calverst...g-how-it-works/
 plus lots more useful infos

I’m under the same opinion.
That’s why I want to delete the bypass hose. I already have the sandwich place with outlet to the bottom rad hose. So bypass is not required for me.

ahhh that brings about another issue. bottom hose or top hose.

Sandwich plate to bottom hose (I think!)

Top hose is only thermostat housing to rad.

 

there is a big discussion if you should feed the hot water from the head into the bottom hose or the top hose.

[KTS]

if i read the Calver article correctly he suggests coolant should always be drawn through the heater tap of the cylinder head to avoid heat build up around no 4 combustion chamber.

 

if that coolant is then drawn through some form of heat exchanger, and so being cooled, then it should be plumbed into the bottom hose.  if it's not being cooled, then it should be fed back to the top hose so it's drawn through the radiator to be cooled before re-entering the block

 

what might work would be a three-way valve in place of the standard heater tap setup so that if the heater is not selected hot water would be diverted back to the radiator, otherwise it flows through the heater matrix and then back to the bottom hose and into the block

 

take-off from the sandwich plate should go to the bottom hose.  the take off should be below the thermostat, so should only really have any significant flow when the thermostat is shut.  there will be some circulation of hot coolant straight back to the pump when it's up to temperature, but the smaller bore of the pipe should minimise this.  the only way to stop it completely would be to fit some kind of reverse thermostat (i.e. one closes at 82degrees) into that line 

Edited by KTS, 26 October 2018 - 08:24 PM.

[timmy850]

The coolant will always take the easiest path. If you don’t have a heater takeoff on the opposite side of the head the coolant will favour the first few cylinders and #4 would be hotter. How much hotter I don’t know.

Another alternative is a dry deck or semi dry deck, as it forces all the coolant through the block from #1 to #4 cylinders, then through the whole head the opposite direction.

I previously had the heater takeoff going straight into the bottom hose. On hot days it made the engine run much hotter till I figured out my mistake.

[Spider]

So what exactly is the purpose of the bypass hose?

 

To drive us bonkers.

 

Supposedly, it's purpose is to circulate coolant in a closed loop around the block, by-passing the Radiator,when the Thermostat is closed.

 

That may sound fine, but it will continue to do this when the Thermostat opens !! Circulating Very hot coolant back in to hot coolant,,,,,

 

As a 'bonus' side effect, with the location of the By-pass on the Pump, they are help bring on the onset of cavitation much soon, while also leading to overheating in itself, also 'aids' the rusting of the cooling jacket bringing on longer term issues,,,,,,

 

It only took Leyland about 34 years to wake up to this and modify the system, though they only went 1/2 way,,,,,,

 

 

 

The Pump is a Centrifugal type of design. The correct way to close these off (to stop or reduce flow) is to block off the Outlet of the Pump. The standard Thermostat will do this quite well. So, circulation through the block via some kinda By-pass, for these reasons is not needed.

But I hear some say all the Hot coolant will go to the top of the head and go no further (when the Thermostat is closed). Yes, it will go up to the top of the head, right up to and including the Thermostat, which will open the Thermostat but before that happens, it will displace the cooler coolant to the lower parts of the block, which in turn will heat and rise, by which time, the Thermostat will have begun to open,,,,

 

The by-pass in what ever form is not desirable. I've been blocking mine off for longer than I care to remember and doing nothing else, not even drilling the Thermostat plate (let the Thermostat do it's job !!!), however, as Nick pointed out elsewhere, the Thermostat should include the 'loose wiggly' in it, though these will float up and block that hole it's in when the coolant level gets up to that point when filling from dry.

 

As for no. 4 cylinder not getting enough coolant flow around it - it does well enough in stock form. Maybe if the engine is really modified AND you like to use all the power it can make very often, then some additional flow maybe needed, however, it's really not wise to start introducing colder flows hapazardly in to already hot flow paths.

 

The Blocks are quite well designed already in this regards. If you ever have a block on the bench, look in through the water pump opening, there's a really good and well designed taper in the cooling jack in the front of block from the pump right down to No. 4 cylinder, giving even-ish flow throughout the block.

 

I've written much in many pages on the forum here about the cooling systems in these cars, take it for what you like, but do a search

[skoughi]

I read Calver's stuff regarding bypass's and all the coolant issues, as a result I ended up removing the heater valve on the head and put on a straight through pipe that leads to a pipe set up before the heater (later heater with the cut off valve next to the heater box) that once the heater matrix can take no more flow it then lets water go into the bottom hose and back into the pump. In my (small) mind this should create a constant flow of coolant right through the block and head when the thermostat is closed. The engine warms up quite quickly, the heater puts out plenty of hot air and the electric fan on the front mounted rad only comes on when the car has been idling for a while. I'm not saying my way is the best or in fact that it actually improves anything as the far more experienced guys are saying there's no need for the bypass, but it does seem to work fine!