You would come to a set of lights and have to wait for a Granny to Pass and its to late then

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Stop Licking the Dog...I Don't Care Who Started It

Because if the air temperature got two degrees hotter you'd overheat again. If you're relying on the colour of your radiator to prevent overheating you need a bigger radiator.

Tim

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1951 Morris Commercial J Type Van
1955 BSA C11G
1961 Morris Mini Traveller
1969 Triumph TR6R
1977 Leyland Moke Californian

Why do they paint them all black? Is it tradition? Or is there something in it?

All other things being equal, if it gets two degrees hotter the car with the black radiator will still be a couple degrees cooler than the car with the white radiator.

ha ha ha ha ha Dam good one Gaf, dam good

Ok,,, lets look at the std aussie 3 core rad,,, there`s ABSOLUTELY no problem with that radiator what-so-ever!!!!!!!!!!!!!!!!!!, the dam things cool both my 1510cc road rocket & my 1415cc full race engine, & a host of 30 plus years of building & repairing & maintaining minis in my life time so far,,, """IF""" a couple of degrees temp difference caused by a different colour paint on your rad is actually the difference between running too hot on your mini, then you`re running too dam hot anyway & there`s OBVIOUSLY another problem somewhere

YES!!! Black is better because!!!!! it helps draw the heat through the metal rad, away from the water, it attracts (for want of a better description) the heat, just as it does wearing a black shirt in the hot sun comparted to a white shirt.

Yes,,, it`s simple physics

BUT!!!!!!!!!!!!!!!!!!!!! for sh!ts sake, this mini radiator argument/mith has been going on for years & years & it`s not a new conversation, it`s not something weired, there`s no Black majic or black art, there`s nothing special about making a mini run @ the right temp... just fix the problem(S) that/are causing any over heating & paint your rad what ever colour you like, the difference will only be a couple of degrees when all else is in good working order

I have a Pirometre (infra red temp sensor,,, digital "point & shoot" type, tell me what temp things are running type thing) & i can assure you that it doesn`t lie

If your mini runs hot, then there is a reason & it won`t be "BECAUSE" of what colour the rad is painted!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

(Just don`t chrome it,,, THAT sh!t does tend to hold the heat ,,,but i`d still has at a guess that it probably still wouldn`t "CAUSE" your mini to run "TOO" Hot,,, Not that i`ve tried it tho, so i can`t say "That" from experience, but i have seen some pretty dam fast minis that have had Chrome rads (or chrome tanks if we all want to get picky, "Little Thumper" is one example if any of you are old skool Brisbane mini people) & they hav`nt run hot.

For Farks sake!!! i`ve actually got to run an 88deg thermostat to get the temp "UP" on my bimmer twinky donk with the ally rad... So, a difference of 2 or even 5 deg isn`t going to make a mini donk run "TOO" hot,,, "UNLESS" it`s running "TOO DAM HOT" allready, & as previously stated & as everyone allready knows,(or should know) the paint on the rad isn`t going to "CAUSE" an issue.

\For farks sake , check your temp guage for acuracy tho, i`ve seen heaps & heaps fo them read way over & the customers have chased & chased an overheating issue , only for me to say that it`s just their temp guage over reading

crickey, there`s lots of worms in this can

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

OK, Matt is absolutely correct. If your mini is overheating, it has something wrong with it that the radiator colour isn't going to cause or fix.

But, some people might like a bit of heat transfer theory without reading that boring text book I referred to. So, here goes:

There are the following types of heat transfer:
Conductive and radiative.

Conductive heat transfer is when the heat energy transfers from one location through a material and into another material through physical contact. The important parameters are the temperature difference, the area of contact, the thickness of the materials and the resitance of the materials to heat transfer (heat transfer coefficient). In transient conditions (as opposed to steady state), the specific heat of the materials is also important. This is the energy required to raise the temperatue of 1 kg of the material by 1 degree. Conductive heat transfer cannot happen across an empty gap (a vacuum).

Radiative heat transfer is when one material loses energy from its surface through radiation. The radiation is in the form of infra red wavelength waves. These waves don't have to be absorbed by something else for the hot material to cool down. Having nothing to absorb the IR is best. Another material may just reflect the heat back. Different materials and different colours radiate and absorb IR at different rates. The vast majority of materials radiate IR in correlation to their visible colour. Black is most efficient. White is poor and a mirror reflective surface is worst. The variables of interest here are surface area, the transmittance value of the material and the absolute temperature of the surface. Note that the transmittance of the surface heavily affects the way those IR temperature measuring devices work. The cheap ones are just calibrated for black, typically mill-scale black of mild steel. Others can be adjusted for the material of interest. So, just because you have an IR thermometer, don't think you can point it at your tyres, then your shiny brake discs and accurately read the temp of both.

What about Convective heat transfer?? Well, it is just a sub-set of conductive where one of the materials being heated is a liquid or a gas. Under this condition the fluid becomes bouyant as it is heated (hot air rises). This moves the hot fluid from the surface and presents new, cooler fluid. Now the heat transfer is faster because the heat is physically moved, not just transmitted through the fluid. This type of heat transfer only works where there is gravity to drive the bouyancy.

So, if you want to keep heat from moving, you need a vacuum gap and mirror reflective surfaces. Take a look at the humble vacuum flask. Inside is a chamber isolated from the outside by a vacuum. The surfaces of the chamber are mirror coated. The only way for conductive heat transfer to occur is the neck where the two parts join and the lid. Radiative heat transfer is retarded by the mirror finishes.

Now, the heat transfer methods work at different rates. Conductive is linear with temperature difference, radiative goes up with absolute temperature (I can't remember the acutal relationship but it becomes dominant when the material becomes glowing-hot. Convective heat transfer goes up with the square of the temperature difference.

We can now answer these questions:
Q1: You are making two cups of tea. You have poured the boiling water into both but only poured the milk into one when the phone rings. After a while you come back and pour the milk into the second one. Which cup is hotter when they are both ready?
A1: The hotter one is the one that had the milk in before you got the phone call. The reason is the temp was lower when you walked away. As we know the convective heat transfer is much faster with hotter materials (squared with delta T) so the un-milked tea lost more energy. All other heat transfer rates were linear and not different between cups.

Q2: What is the black-body temperature quoted by the BOM?
A2: It is the temperature that a "black" object will reach in direct sunlight on a sunny day. It is hotter than the air temperature of the day because a black object will absorb solar IR radiation faster than it can lose the heat through conduction or convection. A black piece of steel will easily reach 70 degrees C in Qld on a sunny day.

Q3: It's not below freezing but we get frost, why?
A3: Surfaces with unshaded exposure to the sky will radiate heat without it being reflected back. These surfaces can become a few degrees cooler than the air around them before the conductive heat transfer from the air replaces heat energy and equilibrium is established. If the air is nearly zero C, then the surfaces can be less allowing ice to form.


Onto car radiators.
The primary steady-state heat transfer mode is conduction to air (sometimes called forced convection). The heat travels from the coolant, through the radiator core, into the fins and then into the air. The heat transfer rate is determined by the difference in temperature between the coolant and the air, the resistance to heat tranfer of the core material/s, the surface area and the rate at which the heated air is replaced by cool air. So, hotter coolant will tranfer heat more efficiently. Cooler air same.

A less resistive core is better. The resistance of two materials in series is the same as two electrical resistors in series. So copper, then paint or alloy then aluminium oxide passivated layer. Better heat transfer properties and thinner materials are better.

Bigger surface area is better, but so is higher rate of air exchange. There is a trade-off here. Higher number of fins gives better surface area but makes the air flow more restrictive.

Getting the hottest coolant to meet the coolest air is the best. Air has a poor specific heat. It heats up quickly without absorbing much energy. So, thick radiator cores are poor because the air heats early in its travel through the core, doing little in the rest. Thin, large-area cores are much better. Most car radiators are large, single core devices these days. We need the air to touch the surface of the fins. Therefore we want a turbulant air flow through the fins so we make the fins wobbly and maybe even put some little jagged cuts in them. Any talk of the air needing to hang-around for a bit to soak up the heat is incorrect.

If we are just trying to dump heat and not aiming for the lowest final water temperature (engine radiator situation) then there is little benefit in multi-pass radiators. On the other hand, if we are making a water to air intercooler we are concerned with the final water temp. This needs to be the lowest it can be so it is more efficient in the inlet heat exchanger. In this application, multi-pass or cores travelling on the long axis of the radiator may be best.

That was a lot of reading about conductive, radiative and convective heat transfer. I haven't gone into chemical reactions (eg absorbtion refrigeration) or change of state (eg vapour compression refrig or those "heat-pipes" you can get for your PC chip or even intercooler water sprays). I also haven't talked about transient state effects of thermal mass and specific heat, which are important to peaky loads like intercoolers. There is also the humidity of the air to consider and I haven't gone there.

Let me know if you want more or you think I'm wrong or should shut up and piss off

Very clear and well put

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David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!

now common Mokesta, how`s about some detailed info then? You`ve barely touched the surface

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

so what are you trying to say?

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Your probably going to get better heat dissipation from making a tight seal so full air passes through the rad and out of the engine bay. You could maybe flex all the grill slats up to allow more air to flow in. Paint sounds like such a thermal barrier but testing will prove either way.

When I did Thermodynamics at uni It was clear air flow over the surface was a major factor in transfer of energy given the material "u" stayed constant.

OK, now you've posted the info you were referring to, don't think this might have been a little outta' line? Considering most of what it says agrees with the early posts! Certainly didn't warrant the "oh dear"....

Anyway there are a couple of points of difference - one that air speed matters. I have done hours of testing on water cooled PC's with radiators and air most definitely DOES make a difference with the heat dumping via conduction. Too higher speed is detrimental to heat transfer....so is too low a speed.

The other point is colour effecting transfer via radiation. All the info I've seen would indicate the colour of the radiator is 'invisible' to the infra-red energy being emmitted. Would be keen to see any other references. It certainly does effect things when it comes to absorbing energy...as anyone leaning on a black car roof knows. It gets hotter than the white car because of it's colour - however if you were to artificially heat that white surface to the same as the dark one, it would burn your hand just the same. Have a think about what colour oil heaters air....water radiators in homes.....


Lastly Matt - don't get us wrong here: we're pointlessly debating the effect of colour on heat loss from a radiator. I don't think anyone is actually suggesting it will make enough of a difference to matter in a car! It's the 'how' not the 'how much'. Kinda like holes in cam followers [/i]

On the topic of testing the effects of cooling mods:
Has any one tried soldering baffles in the rad tanks to make a "triple flow" type rad?

Any good? Seems like a relatively simple way of trying to lower the water temp, especially if you're already pulling the tanks off to clean the core.


http://www.aussiedesertcooler.com.au/triple_flow.htm

desert coolers do some bad ass radiators..

Set your face to stunned when you ring for a quote!

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haha yeah I'm sure, but the idea would be pretty simple to apply to a standard radiator.

Me thinks anyway.

They also seem to have a great affection to the 'can o' matt black' paint job.

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T