Aluminium Radiators - How good ?

[Hybrid_From_Hell]

Yup, 90 heater connected to the system

Lower stat bring heat down

It did have the old racer trick of a plate with drilled hole, as racers don't like thermostats as if it jams then engine at High RPM = toast,

so they bung plate in, the trick of 3 x 3mm holes in thermostat is a well known compromise

No stat also gives caviatation which worsens cooling !

Nige

[Ash.Witty]

Also it might sound daft but have you tested the thermostat to make sure it works?

[Hybrid_From_Hell]

Yes fan wired right way around !

[Hybrid_From_Hell]

Thermostat is brand new genuine and yes it works !

[Ash.Witty]

Hmmm what dimensions and how many cores are the rad, my 4.2 was originally 3 core until my viscous fan propelled its way through it, I then had a 4 core 're-core as I planned a 4.6 TT install with a twin speed kenlowe and a set of p38 air con fans on. It would get up to temp then go down to 82'c where it would stay there all day unless I booted it say down the bypass where it would only get to 87'c.

Why not add another core?

[Boothy]

Have a looksy at Summit racing aluminium rads (thinks mine was 5.7litre 1" cored rad) for about £200 quiddies plus a bit of delivery and it took 2 days to arrive.

Faultless. Electric water-pump, no thermostat or speed controller, 16" Pacet Profan on thermo-switch blowing and opposite side 12" Spal just as a booster in times of need and covering the rest of the rad.

But also have a look at the waterless coolant as well its supposed to be the dog's.

TTFN

[TheRecklessEngineer]

But also have a look at the waterless coolant as well its supposed to be the dog's.

I will (and have done in another thread) dispute that quite strongly.

[Dave W]

Vents in the wrong place can reduce airflow through the rad, especially as you increase speed. Have you tried covering the vents ?

You need a low pressure area behind the radiator to get a decent airflow, adding vents can increase the pressure at speed, reducing airflow through the rad.

Steering guards can also cause similar problems as air leaves the trailing edge of the guard and circulates upwards onto the rear of the radiator.

[Hybrid_From_Hell]

Good point on steering guard !

Vents are on the back rear section of the sides of wings put in to help the cooling of the old 4.5

They did help many peeps talk of cutting holes on the edges of rear of the bonnet curve where they join the tops of the wing I am unconvinced and think those make air just bypass the engine ?

[Hybrid_From_Hell]

On a side note

Anyone know the optimum amount of antifreeze that gives the maximum cooling benefit ?

Also does red or blue have any benefits on cooling ?

N

[Dave W]

OK, I'll start off by saying I'm very much an "interested amateur" when it comes to all things aerodynamic, this is all based on other people's research that I've picked up over the years ! You may want to skip to the last sentence of this post if walls of text offend you

To get air flow through a radiator you need a higher pressure at the front of the radiator than at the back. It's a common misconception to assume that the "ram air" effect is enough to cause that pressure imbalance. The faster you go the more air is forced through the radiator ?, no. The only way of increasing air flow through a radiator is by increasing the difference in air pressure between the front and rear of the radiator.

Badly placed vents often improve under bonnet temps at low speed allowing convection to do it's job but as you increase speed the exterior pressure increases, causing air to move into the engine compartment through the vents, effectively increasing or balancing out the under bonnet air pressure. In simple terms every bit of air moving in through the vents reduces air through the radiator by the same amount. It is even possible to reverse the air flow through the radiator with badly placed vents at the bottom of the windscreen, even at very high speeds.

Cutting holes in the rear of the bonnet curve is probably the second worst possible place to put vent holes, second only to the trailing edge of the bonnet near the windscreen. They will work fine at low speed thanks to convection but as they are in a high pressure area the faster you go the more they will increase the under bonnet pressure, reducing air flow through the radiator.

Being at the highest points in the bonnet gives many people the misconception that they work really well because "when parked you can really feel the heat coming out of them". The reality is that that is just convection doing it's thing and bears absolutely no relation to their effect when the vehicle starts moving and you move from basic thermodynamics to aerodynamics.

Car manufacturers position fresh air vents in those positions and engine air intake scoops are often sited there too because when the vehicle is moving those points of the vehicle are high air pressure spots. Ask yourself where Land Rover sited the engine air intake for the TDi and TD5 Defenders ? I doubt they'd deliberately position an engine air intake in a low pressure area, although granted I wouldn't put it past them so maybe not the best example

Normally the lowest pressure areas are around the front of the bonnet, not the rear. The best position for a cooling vent is normally just behind the radiator with the vent having a lip at the front edge that reduces the pressure even further immediately behind it. You can see the effect when it's raining and you're travelling at highish speeds in a Land Rover, watch where the water seems to form a pool just behind the front edge of the bonnet. If you look at a lot of track saloon car designs they often have the rear of the radiator completely enclosed by a duct that exits through a slot just behind the leading edge of the bonnet. A lot of that is for handling performance reasons (avoiding hot air being routed under the car) but it also improves radiator air flow ensuring a good pressure differential at high speeds.

In short, cover up the vents, take it for a spin and see if it helps, you never know

[Bowie69]

I'd also question why run a 78C stat, then switch the fans at the temps you say....

Also,.hotter water = more efficient cooling from radiator, due to greater temperature differential.

I'd consider simplifying the hoses, on my set up, I have a large diameter to small T in bottom hose, which runs off to heater, the rest is pretty much as standard 3.9 non-serp.

[elbekko]

The viscous fan + a good cowling should be plenty, having electric ones too seems a bit silly and is probably working against you.

The tighter the tolerances on the cowling, the better. I can imagine with a custom rad setup the cowling probably isn't optimal, unless you custom made it.

The picture earlier in the thread of the radiator with two fans without a cowling is just painful, that way the fans won't be used to their full potential.

Just my opinion of course, but it should never be a case of "throw more fans at it", because at some point you're just hurting airflow.

Bowie, not sure I agree with the lower stat = lower temperature differential. If the coolant is at 90°, it shouldn't matter if the stat opened at 77 or 83.

[jad]

Is the viscous fan working correctly?

[Hybrid_From_Hell]

Lower the stat the lower the engine temp will maintain or try to

Race v8 should be around 75-85 degrees more hear than this sees drop on power and increase on wear

Some v good food for thought there Davd will have another read or 3 of that and other info in the various replies and look at if any can help

Stat us I think a early 74 degree ind too !!

Nige

[Hybrid_From_Hell]

Jad

That's an idea to check !!

How exactly do you check if a viscous fan is good / had it ?????

[jad]

Think the general method is to put a news paper into the fan when the engine is hot. If the fans not working correctly the news paper will stop it rotating.

Jad

[steve b]

.......if its working you will feel several hundred cfm of air coming out the back of it ?

of course shredding a newspaper will be more fun

cheers

Steveb

[FridgeFreezer]

needs both when slow and hard worked

Well, yes, but that doesn't mean they help each other when you're at road speeds.

Good points about aerodynamics, good point about the viscous actually working!

I have to say I think the "lower stat = better" argument is more a folklore band-aid than good practice, as said above the greater the temperature difference between the rad & the air, the more heat will get dumped. Modern engines (and every RV8 since about 1980-something) has left the factory with an 88deg or 92deg stat, modern oils are designed to work better when warm (you can run too cool for the oil to work properly).

I am almost certain that your existing rad is up to the job and the problem is in the overall setup / system.

[SeriousIIa]

Mated to my 5.7 I have an Allisport uprated V8 radiator, with 2 16 inch spal fans, and it now runs substantially cooler then before with a standard radiator. So another vote for upgrading.

[Hybrid_From_Hell]

The thermostat / running temperature issue is one I have explained to peeps on numerous occassions,

some do get it, but many don't, its one of those weird things to grasp in your mind !!

V8s have differing thermostats, some for making the various engines run at differing temps (the 4.0 / 4.6s

were made by BL to run hotter to aid emissions, and as a result ran hoter than the design really wnats,

and added to overheating / liner issues), and often for differing climates. My system SHOULD control itself

and maintain target temperature WHATEVER the weather / how hard worked, if all was right, having an electric

fan to try to get on top of the issue is wrong in all but the most extreme moments maybe - the more reliant I am

on "Extra" fan(s) the more wrong something is basically in the system

The idea of all thrmostats is to speed up warm up from cold, and then to help maintain a target

temperature via opening and closing - we will forget the mad octopus nightmare of the GEMS system, as they are a horrible

cobble up, when you understand that one of the KEY reasons they did it was to make the Interior warm and cosy faster than the

engine geting up to (too higher) temperature, a sort of typical LR Cock up

So, standard V8 thermostats come in a selection of flavours, here are the ones I have coded and squirelled away

Most V8s should aim to run between 75-80 degress to be happiest and product greatest BHP,

tricky when the lucas efi system in on enrichment until 80 degrees !! (MS WUE is 72

72 Degree Therm = Target of 75 Degrees Running

77 Degree Therm = Target of 80 Degrees Running

78 Degree Therm = Target of 81 Degrees Running

82 Degree Therm = Target of 96 Degrees Running

What you should do is have a logical choice for which thermostat above to have in your engine, prob based on the target temperature,

in this case I have either the 72 or 78 Degree Thermostat (can't rememeber now which !!) then OVERCOOL the engine via Pump / Rad / fan

etc, and the thermostat regaulate the temperature.

If it doesn't (ie in my case) then there is an issue with the cooling system not being enough, and thats where I think I am

at the moment. The 3 x 3mm holes drilled into the Therm unit is that as you are now having the thermostat control the target temperature

it will work harder than in a normal road car, so the failure of it racing = big engine over heating, so the 3 x holes is a trick

that gives some control if it jams, and some warning. Some come with one hole which is a bleed hole, but 3 x is regarded as a many / big

as you can go without upsetting the target temperatures.

Many race engines just have the thermostat chucked away and a restrictor plate put it with a selection of holes to give the traget temp,

the 5.2 had a 22mm hole, the downside is that the engine now would take an age to heat up.

From tlaks I have had with some peeps who do this sort of thing for a living is that I am at the moment doing pretty much all the things I should

(Big Rad , Antifreeze, cowling, low thermostat, fan(s) etc etc ) but vthat possibly the engine in its state of tune, and heat outputs requires

more than the system can give, so target termps only OK when its not being worked hard.

Add a hot summers day (oh yes pease ) and it will make things worse.

Seems an Ali cross flow rad, with a Made to fit perfect Cowling, and a few tweaks may be on the cards

Will defo check the viscous is working, something I had just not considered

Hope nthe above is of use to others not or in the future

Ho Bludy Hum

Nige

[David Sparkes]

Jad That's an idea to check !! How exactly do you check if a viscous fan is good / had it ?????

Based on my experience with a 38A, there can be a more precise method than shredding newspaper.

Bear in mind that a fan viscous coupling does NOT work in the same way as a transmission viscous coupling.

First a couple of static tests.

Wipe your clean fingers along a couple of the blades. Is the dirt now deposited on your fingers oily?

If the fan is covered by a cowling, wipe the inside of the cowling with your fingers. Is the dirt now deposited on your fingers oily?

Look at the underside of the bonnet. Is there a line of oily dirt running from left to right above the fan?

Any oil found in these checks is probably oil from the VC being flung outwards by centrifugal force. Obviously the VC should be oil tight. These checks may be invalidated if the fan is regularly blasted by muddy water.

Dynamic testing.

When left to stand overnight, all the oil in a fan VC settles in the bottom of the VC, effectively coupling the inner (shaft) to the outer (blades), making the coupling 'stiff'. Flick the fan round with your fingers, observing how many blades pass your finger tips after the flick. It should be a low number.

With the bonnet open, start the engine, listening for the roar of air being moved by the stiff coupling. Hold your hand, or a piece of card / stiff paper over the gap between the fan cowling and the engine block. You should see and hear the effects of a strong movement of air. Blip the throttle just once or twice, 2000 rpm max is fine, you are listening for the rise and fall of the roaring sound of the air movement. Mentally record the sight, sound, and feel. Use a video recorder (with microphone) if you want.

Leave the engine ticking over. After a minute or so you should realise the air roaring sound is diminished, and the effect on any card or paper monitor much reduced. This is because the VC oil has been centrifuged into its 'working' position, reducing the coupling between the shaft and the fan.

Stop the engine, then flick the fan round with your fingers, observing how many blades pass your finger tips after the flick. It should be a high number, compared with your earlier test.

By now, you should have been able to form a clear opinion of any VC changes between it's initial stiffness, and its free running 'cold' state. If there is minimal change the VC needs renewing.

For a final test, run the engine until the temperature is 'too high' in your judgement. Blip the throttle, in the 38A, with all its sound proofing, I could hear the enhanced air roar inside the car created by the coupling changing from soft cold to hard hot, so you should be able to hear the enhanced roar in yours. Final check is to stop the engine while hot, then flick the fan round with your fingers, observing how many blades pass your finger tips after the flick. It should equate to the low number of your first test.

Note that fan VCs for diesel engines create greater stiffness when hot (providing less slippage between shaft and fan) because the diesel engine rotates at a slower speed than the petrol engine. Coming from an overheat situation, you may be tempted to fit a diesel fan VC, but I would advise against it. You have spent a lot of money to get your engine horsepower, there seems little point in wasting it to drive a fan harder than necessary.

One last observation, the fan VC has to blow the air out of the engine bay, but if your bay is no worse than standard, that should not be a problem. With that proviso, it is the (correctly working) VC fan that provides the low pressure behind the radiator that the electric fans blow air into.

HTH, and Good Luck.

[Hybrid_From_Hell]

^^^

Superb, many thanks Dvaid

N

[Bowie69]

I have to say I think the "lower stat = better" argument is more a folklore band-aid than good practice, as said above the greater the temperature difference between the rad & the air, the more heat will get dumped. Modern engines (and every RV8 since about 1980-something) has left the factory with an 88deg or 92deg stat, modern oils are designed to work better when warm (you can run too cool for the oil to work properly).

This is what I was trying to explain, but very badly, in the wee hours last night

[rick]

OK, I'll start off by saying I'm very much an "interested amateur" when it comes to all things aerodynamic, this is all based on other people's research that I've picked up over the years ! You may want to skip to the last sentence of this post if walls of text offend you

To get air flow through a radiator you need a higher pressure at the front of the radiator than at the back. It's a common misconception to assume that the "ram air" effect is enough to cause that pressure imbalance. The faster you go the more air is forced through the radiator ?, no. The only way of increasing air flow through a radiator is by increasing the difference in air pressure between the front and rear of the radiator.

Badly placed vents often improve under bonnet temps at low speed allowing convection to do it's job but as you increase speed the exterior pressure increases, causing air to move into the engine compartment through the vents, effectively increasing or balancing out the under bonnet air pressure. In simple terms every bit of air moving in through the vents reduces air through the radiator by the same amount. It is even possible to reverse the air flow through the radiator with badly placed vents at the bottom of the windscreen, even at very high speeds.

Cutting holes in the rear of the bonnet curve is probably the second worst possible place to put vent holes, second only to the trailing edge of the bonnet near the windscreen. They will work fine at low speed thanks to convection but as they are in a high pressure area the faster you go the more they will increase the under bonnet pressure, reducing air flow through the radiator.

Being at the highest points in the bonnet gives many people the misconception that they work really well because "when parked you can really feel the heat coming out of them". The reality is that that is just convection doing it's thing and bears absolutely no relation to their effect when the vehicle starts moving and you move from basic thermodynamics to aerodynamics.

Car manufacturers position fresh air vents in those positions and engine air intake scoops are often sited there too because when the vehicle is moving those points of the vehicle are high air pressure spots. Ask yourself where Land Rover sited the engine air intake for the TDi and TD5 Defenders ? I doubt they'd deliberately position an engine air intake in a low pressure area, although granted I wouldn't put it past them so maybe not the best example

Normally the lowest pressure areas are around the front of the bonnet, not the rear. The best position for a cooling vent is normally just behind the radiator with the vent having a lip at the front edge that reduces the pressure even further immediately behind it. You can see the effect when it's raining and you're travelling at highish speeds in a Land Rover, watch where the water seems to form a pool just behind the front edge of the bonnet. If you look at a lot of track saloon car designs they often have the rear of the radiator completely enclosed by a duct that exits through a slot just behind the leading edge of the bonnet. A lot of that is for handling performance reasons (avoiding hot air being routed under the car) but it also improves radiator air flow ensuring a good pressure differential at high speeds.

In short, cover up the vents, take it for a spin and see if it helps, you never know

All true.

I've proven those high pressure regions on a Patrol and Deefer with wool tuft testing.

Lifted the trailing edge of the Patrol bonnet and all the wool tufts flew back under the bonnet (as I expected them to)

Undid the blank cover on top of the RHS wing of the Deefer and we had massive turbulence and inversion, ie. the wool tufts were going back into the hole, not going out.

A hole in the side of the mudguard behind the front wheel (where the air inlet is for the engine, but opposite side ) seems to work well at evacuating the underbonnet air.

Another observation re fin pitch, a mate of mine was one of the engineers on the Aussie Perentie 110/6x6 project for the ADF back in the eighties.

The first lot of rads they used resulted in overheating. They'd increased the fin pitch to increase the cooling capacity over standard.

They then reduced the fin pitch, ie, increased the fin spacing to cure the problem.

Goes against theory in reducing the surface area, but it worked.

The engineers felt the air was packing up in front of the rad at speed with the increased fin pitch, my theory is that the underbonnet air pressure was too high and the air wasn't escaping fast enough, reducing air flow through the core. As already mentioned, you need pressure differential for flow.

I'm wondering if the reduced fin pitch allowed more air to be forced through, (less resistance to flow) helping to push the underbonnet air out faster, much like Tdi's overheat here when travelling at speed if their viscous fan is buggered. Install a new fan clutch and problem solved.