Coolant Mystery

[Mr. V]

I've not used the heater for quite some time. When I did it worked well, as I recall. The tap on the rear of the block has been closed since then. The return from the heater goes through the inlet manifold, so when it's turned off the manifold isn't heated.

The fan belt used to slip, and it is since replacing the head gasket and properly tensioning the belt that this problem seems to have started (however I can't see that as anything other than a coincidence). Anyway, I'm going to take the water pump off and have a good look at it.

[Mr. V]

Having read different threads on achieving even coolant distribution to all parts of the block, it seems that the conventional wisdom advises that I should be running the car with the heater on all year round. Is that correct?

[rocco]

Do you have any idea how old the pump is? If it's looking a bit tired and you're taking it off anyway, maybe consider replacing it regardless of whether it is fault or not. They are only about 20 quid.

https://www.morrisminorspares.com/cooli ... er-p829649

To save the hassle though, you could just take off the fan belt and the hose and turn it by hand to see/hear if it's turning the propeller. There is nothing more to it than that as far as I know.

[myoldjalopy]

Having read different threads on achieving even coolant distribution to all parts of the block, it seems that the conventional wisdom advises that I should be running the car with the heater on all year round. Is that correct?

The theory is that leaving the heater tap permanently on allows better circulation of the coolant at the rear of the engine. I leave my tap on for this reason but also I can't be bothered to turn it on and off again as the seasons pass!

[oliver90owner]

Having read different threads on achieving even coolant distribution to all parts of the block, it seems that the conventional wisdom advises that I should be running the car with the heater on all year round. Is that correct?

That makes me wonder why the valve was fitted in the first place. It was included for a good reason.

[philthehill]

Later 'A' Series engines had coolant circulating out of the rear of the head at all times. The heater was controlled by a remote valve that allowed uncontrolled coolant to circulate through it and back to the head via the sandwich plate fitted between the head and the thermostat cover. When the heater was required the control valve directed water through the heater element.
Because of the constant circulation of coolant there was no requirement for the bypass hose. Later heads fitted with the constant flow system did not have the bypass hose facility. The head was just a solid casting in that area.

[win]

I presume this was to give better cooling around number 4 cylinder, did it work?
I think I have one. Is it a big advantage.
Regards Win

[philthehill]

The 'A' Series has always suffered with poor coolant circulation around the rear of the head.
I suspect that the reason for adopting the constant flow circulation was to overcome the poor head circulation.
The performance classic Mini people have overcome the poor circulation problem by blocking all the block to head transfer passages and fitting a large dia transfer hose between the rear of the block and the rear of the head. This does require machining of the head but it does ensure that all coolant is forced to the rear of the head.
Unfortunately I cannot do that mod on my Minor because of the close proximity of the damper mount cross member. What has been done is to put an additional transfer hole in the block at the rear and have a constant flow out of the heater take off stubb and back to the bottom hose via a oil/coolant intercooler. I have also retro fitted the thermostat so that coolant is directed to the rear of the head.
As regards does it work - the constant flow factory system works very well. The classic Mini mod exceptionally well and the mods to my Minor keep the engine within the correct temp range.

[Mr. V]

I've had the water pump off (it's the cast impeller type) and all seems well, so there we are:
Thermostat OK
Water pump OK.

I still can't understand why no mixing and no overheating!

I shall flush out the radiator and block/head and see what happens. It all seems rather pointless if it's not overheating.

Thanks everyone for your contributions.

[Mr. V]

Oh, by the way, and apparently contrary to what I've read in some threads, in order to remove the water pump you don't have to remove the front panel or even the grille. Once you've taken out the radiator there's plenty of space to work on the front of the engine.

Someone might appreciate this, possibly.

[kevin s]

One way to maiintain flow to the back of the head would be to fit one of these in the hoses instead of the original tap, diverts the flow rather than blocking it.

https://www.ebay.co.uk/itm/174479166499.

hoses are probably a bit bigger (5/8 rather than 1/2") but thats pretty easy to overcome.

[Mr. V]

Interesting. I had thought of some sort of valve that could apportion the flow from the rear of the head to the heater, and/or direct to the radiator bottom hose in variable proportion.

That would fit the bill as far as maintaining coolant flow round the back of the head is concerned.

I suppose, ideally, the output from the heater should pass to the bottom hose and the direct return to the top of the rad.

Hmmmmmm.

[philthehill]

The valve in the link above is similar to that fitted to later BL cars.
Allowing a constant flow to and through the back of the head and return to the bottom hose should be the aim.

[Mr. V]

Thanks, Kevin. Sorry to question one of vastly more experience, Phil,but wouldn't the best arrangement be to have the direct return (heater off) routed to an A+ sandwich plate (where, admittedly, it looks like there will be a problem with the top hose alignment with the Morris radiator) and have the heater return to the bottom hose? And if that is a legitimate arrangement would that render the by-pass hose redundant?

[philthehill]

Mr V
Basically that is what happens with the later 'A' Series which has a return to both the sandwich plate and the bottom hose dependent upon which way the heater control is switched. I went some of the way to describe the arrangement in my post of the 30th Aug 2024.
There is no need for a bypass hose with the latter arrangement. The bypass hose was fitted to allow some circulation through the head before the thermostat opened. There have been reported occurrences of valve sticking in the guide if the bypass hose is deleted due to localised hot spots then being formed. I have to say that I have never experienced valves sticking when the bypass hose is deleted.

[Mr. V]

Thanks for the comprehensive reply. You have confirmed my rather shaky suspicions! As may be apparent I'm slowly learning my way around the (peculiar)cooling system.