19 replies to this topic

[Hpal]

Hi, I’m in Australia and I’ve recently bought a 1968 Mini Deluxe (a re-bodied mk1 Cooper S) with a pretty warm 1330 in it. My question relates to coolant hose routing. It has a hose on the heater tap take off point which currently goes down to the bottom radiator hose. I realise this may be detrimental to the engine temp in very hot conditions which we see here. I have heard that routing this hose into the top of the thermostat will help this slightly. Looks like a MG Metro style sandwich plate is a good solution. But I’m not sure which one I need eg temp hole drilled or not (might be an option for running an electric fan one day), which way does the outlet point? And will having one affect the radiator bracket or will it need modifications? There is one with a stud hole for the radiator bracket or one with the threaded sender hole, but not both.
If I require more cooling, I thought about running the bypass hose round the front of the engine and through a small heat exchanger and back to the top radiator hose.
Cheers everyone ☺️

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Edited by Hpal, 31 October 2025 - 05:37 AM.

[imack]

Alternatively, there's the Swiftune take on it. Never seen the hoses listed on their website though.

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[nicklouse]

I would refit the interior heater. Just the extra water volume will help.

 

and those are all designed to go under the thermostat.

 

there is always a big debate about returning the water back into the top “hose” or the bottom hose.

cleanlyness of the block and the cooling system is way way more important. As is the correct coolant and its mix.

[KTS]

another alternative is to create another entry point into the radiator (ally radiator gives the option of getting something welded in place)

 

https://www.theminif...ckup/?p=3752490

[Spider]

As Nick alluded to, the system was designed, if coolant is to be taken from the back end of the head, to run through a heater core, thus dissipating heat there, before being returned to the lower hose. If you 'return' it through a sandwich plate as you are thinking, there's a restriction in the radiator outlet of the sandwich plate that will actually cause the hot coolant on the opposite direction, when there's medium to higher flow rates, so taking hot coolant from the main outlet of the head (at the thermostat) and sending it back to the other end of the head.

If you want to plumb it up in the way you are wanting to, it really needs to be returned to the top tank of the radiator;-

 

.

 

But this pic also brings me to pass on some advice;- toss your Aluminum Radiator on the scrap bin. They kill these engines.

 

Here's the inside of the thermostat housing from the engine to which that radiator was fitted;-

 

 

The brown is rust from the block and head.

Thermostat Housings are made from a particular alloy blend, they are designed to be a sacrificial anode. If there's any reaction between the coolant and the cast irom block and head, the Thermostat Housing should corrode, thus saving the block and head.

With the mix of reacting materials in the car that this was taken from, that included the radiator here ^, it caused the block and head to rust out in a big way. The Head was a write off and the block, while being able to be saved at some considerable cost, isn't brilliant. You can see in this photo, that the sacrificial anode, (the thermostat housing), apart from the rust stain, is in perfect condition, no corrosion at all. Coolant supposedly suitable for this set up was being used, when I drained it, it came out perfectly clean and looked very good. I know many people run these radiators and like them, but I doubt they are aware of the longer term damage they do. They have two things going for them;- They are cheap to buy and they look bling, after that, they are very much a backward step, their cooling capacity too, is no were near as good as a cooper / brass radiator.

 

[Hpal]

Thanks Moke and others for your insight :)

I may refit a heater one day but that's not on the cards just yet, I think I'll scrap the sandwich plate idea as tasty as that sounds  and go for either a small heat exchanger in line behind the grill from heater take-off back to bottom hose, maybe with a fan of some sort, or fit a big electric fan on a thermostat on the main radiator.

[Ethel]

If you fit a sandwich plate, you'll raise the outlet for the top hose too. So you might also find yourself wanting a Metro or SPI style 'stat housing. Note that the Metty & later Minis also used 5/8" heater hoses instead of 1/2".

 

 

The only way you'd lose cooling capacity is if feeding in to the bottom hose reduces flow through the radiator enough to decrease the exit temperature. I can't see it doing that very easily, as the pump was intended to pull on a heater as well as the radiator. You could always play about with a restrictor valve in the heater line & see if the cooling improves the closer it gets to closing

[Hpal]

So, I've had another think and I'm leaning towards using an auxiliary cooler (small radiator) and fan to pre-cool the head water from the heater takeoff point before returning it to the bottom hose, it will be turned on and off with the 10" electric fan I will fit in the wheel well. Then, I thought, what's stopping me putting a standard (kevlar) hose on the lower hose with no tee in it, and using a tee'd bottom hose on the top by trimming it to length and then I can put the water from the head straight into that, which will then also get cooled by the radiator. The mini is really not liking our Aussie summer right now and needs some extra help.  Should I consider a cooler themostat?

Edited by Hpal, 22 December 2025 - 06:20 PM.

[Steam]

I would suggest that if you are having cooling issues now then you have other problems underlying in your cooling system.
A fairly warm 1275 running a standard rad, clean, an 82C thermostat, a small aux rad from the heater takeoff in summer or heater in winter and I run the fan backwards to "lose" a little bit, gives mid on the gauge which measures 92C at the top hose. Yours should be somewhere near the same if your cooling system is not compromised.

[68+86auto]

Get rid of the aluminium radiator.

 

What temperature is it actually getting to and has it been verified with a second gauge.

 

IF it is in fact running too hot (like above 95 degrees), the first thing I'd do is check the timing and fuel mixture throughout the RPM range. The advance curve is important. New distributors can be wrong and old ones are usually worn but can be fixed.

Edited by 68+86auto, 23 December 2025 - 01:25 AM.

[nicklouse]

One thing that has not Ben mentioned about the Metro set up. The heater (in car) is a constant flow item unlike the Mini.

 

i would not be blocking off the opening at the number 4 end of the head as that is the hottest part of the head with the worse flow.

 

Putting the hose form the head into the top or the bottom hose makes little difference. The rad can only cool a fluid by so much. Adding the hot to the hot or the cooled will result in the same temp entering the engine. The only way to get the temps down it to increase the ability to exchange the heat out of the system or have a greater ability to hold the heat. So more cooling surface/more airflow or more liquid. The first part can, to a degree, can be aided with a water wetter this improves the heat transfer from the coolant to the metal. Also do not use a coolant mix of over 50% as that reduces the heat transfer ability of the system as glycol is a poor heat transfer fluid. Never use the waterless coolant. As that is pure glycol and will just reduce the ability of your cooling system.

[panky]

Not sure if this will be helpful as it wasn't on a Mini but on my Sunbeam Rapier engined Commer camper - but the set up should work on any engine.

To draw a few more horses out of the engine I fitted a Davies Craig water pump and a temperature controlled electric cooling fan which worked well but the coolant temp hovered around the fan setting causing it to cut in and out constantly. After a good think I fitted a small motor bike rad (KTM 125) into the heater return piped into the bottom hose (pump inlet) of the main rad. This had the effect of dropping the coolant temperature about five degrees so now the fan only cuts in after a motorway thrash or sitting in traffic for a while.

[Hpal]

That is helpful and relevant, i've purchased online a small radiator and electric fan which i will run my heater take-off point coolant from the head before sending it back to the lower hose. This coupled with a 10" fan on a temp switch in the bottom of the radiator will help I think. Some other ideas are, check the thermostat, and throw a new water pump on with a higher capacity. And i've got the 11 blade plastic fan to go on to replace the 4 blade steel fan. So i've got a few things to try anyway 

[Spider]

The volume of air that a fan can push is pretty much proportional to the input power it takes..

 

The standard cooling fan takes between 3 and 5 HP and as there's little pressure drop between the engine bay and the wheel arch, the standard fan is needed all the time. Cars that have a North / South engine arrangement with a radiator in the front are different in that when moving, there is a natural movement of air here (a pressure drop).

 

The best electric therm fan I have ever found is 450 watts or just over 1/2 HP, though there maybe some bigger ones around now. Even if you found one that was 750 Watts (1 HP), it's still only going to push well short of the volume of air that's needed and only be a restriction to the air flow from the standard fan (if it's still fitted). A 750 Watt fan would draw somewhere north of 60 Amps, so you need a big alternator and wiring for it.

 

They can be helpful in start - stop traffic though.

The best factory fan is the 6 blade type.

[Hpal]

Moke, what are your thoughts on a higher flow thermostat, can pick up one at Supercheap with allegedly 30% more flow, couldn't hurt to try one i guess.