Additional Cooling Options

[ThreePointFive]

I'm thinking through some options on increasing under-bonnet air flow. I have an Allisport radiator which is very effective but the bulkhead gets very hot as there's nowhere for the heat to go. It's been suggested I put some speed holes in the rear side edges of the bonnet, that's not happening. Any option has to be as unobtrusive and look standard externally.

I am using a 300TDi wing for the engine air intake and I have fitted a 200TDi wing as well (as have many others) to gain the additional side vent and help hot air leave but I think this could be better. I have a suspicion it's only really effective at speed when cooling isn't an issue anyway, but off road it is more appreciable that air is not moving. I also have the driver side wing top vent open.

The most obvious thing I can think of is an IP67 PC fan attached to the passenger wing vent to actively draw the air out, but the size of the vent means that will be a small fan. My thoughts - and reason for posting - is that it'll be either so small as to have no additional effect or actually become an obstruction when air flow in (at speed) exceeds its ability to move the volume of air. I welcome thoughts on that. I am unsure if that pressure on the 'in' side may stress the motor or not as it's not an expected scenario for this type of fan.

I could look at one for the top vent, but let's assume this is just the side one at this point.

There's plenty of fans available, such as:

https://uk.rs-online.com/web/p/axial-fans/2303041?cm_mmc=UK-PLA-DS3A-_-google-_-CSS_UK_EN_ePMax_Prio3-_--_-2303041&matchtype=&gad_source=1&gclsrc=ds

This is 12v DC and IP67 so should be plug and play. I could create a simple circuit to feed this whenever the ign is on, or being more elaborate, wired into the thermostat for the main rad fans. Pros and cons to both:

On ign will mean constant noise and battery drain when the engine may not be running, they will wear out faster and be on when they're not necessarily needed.

On thermostat will mean the fan will be an obstruction when not running, which may lead to a loop where they're more likely to come on sooner in the first place.

This could be urinating into the (hot) wind or a genius solution, does anyone have any thoughts?

 

[FridgeFreezer]

I'd question whether hot air is the problem - with a V8 I suspect a lot of it is being radiated directly off the exhaust into the bulkhead and cooling the air in the engine bay won't make much difference.

A shield between bulkhead & exhaust would be my 1st thought.

[ThreePointFive]

I think you're right and that's a large part of it, but with insulation on the bulkhead and heat shield material attached to the top surface of the exhaust, I've done all I can reasonably do for that. 

[elbekko]

I doubt that little fan is going to do more than what your rad fan already does.

What would probably help more is ducting the hot air away, but that's easier said than done.

[FridgeFreezer]

1 hour ago, ThreePointFive said:

I think you're right and that's a large part of it, but with insulation on the bulkhead and heat shield material attached to the top surface of the exhaust, I've done all I can reasonably do for that. 

Is it shiny foil-backed insulation?

How hot is it actually getting inside? I've got a pair of V8 trucks with no insulation and while it does get warm on a hot day off-road I would not say it's unbearable.

Is the heater actually adjusted so that it's not blowing warm air through?

I'm with Ben that a PC fan is not going to move much air, I'd be looking at things like motorbike rad fans or the cooling fan from a Mini power steering rack, or even just a 2nd Defender heater fan.

RS are quoting 40CFM for that fan, Spal quote ~300CFM for a random small fan I picked on their website.

[uninformed]

Defender engine bays are poor at flowing air. This got worse over the years with more “engine” filling the bay and power output increasing.

Aus delivered 300Tdi AC cars had an external thermo fan fitted to help the viscos fan as they had cooling issues under load in summer. 
 

Driving around in the passenger seat of my mates modified 118 special found the addition of the guard side vent was making a difference. Being on his rural property out west (out back) in summer and I could feel the hot air coming out the vent. This at low speed up to 80km/h (much faster than that and I wasn’t comfortable leaning outward etc to reach it.

 

I did this mod on my own 110 and found an improvement in coolant temps. 
No fan was required, as the engine bay is more restrictive than what’s trying to get through the frontal area. 
 

I would also strongly suggest anyone thinking about vents or scoops anywhere on the bonnet or tops of guards do some basic wool pile testing. Airflow in this area is funky at best 

[FridgeFreezer]

12 minutes ago, uninformed said:

Aus delivered 300Tdi AC cars had an external thermo fan fitted to help the viscos fan as they had cooling issues under load in summer. 

I think almost everything that got AC also got helper electric fans, Range Rovers definitely did (so I'd assume Disco did too), as did Freelanders - probably not an Aus thing as much as an AC thing as you're putting another heat exchanger in front of the stock rad.

[Daan]

Have you done any exhaust insulation yet? That's where I would start. With a V8, you have 2 exhausts, which are getting very toasty. So wrap the down pipe and ceramic coat the manifolds. You can also try to lift the bonnet at the bulkhead end to create a gap between the bonnet and wings to let more air out.

[Bowie69]

I think you went stainless y-pipe? If so a ceramic coating may well help there... A lot of the heat, as Daan points out, is the exhaust, especially as it gets pretty close to the floor/bulkhead. 

Shielding from radiant heat really helps too, just needs a bit of tin and an air gap between it and either the heat emitter or the surface you are trying to keep cool. 

To put your PC fan in context, my Spal radiator fan fitted to LGT is 2200cfm.... I doubt it would do much in all honesty. 

Your rad fan is electric too, yes? You could duct it to push the air down and out the bay, but I do wonder why you would be suffering more than an old series with no heat protection at all? 

Holes in the bonnet are, as you say not happening, but the other annoying thing about them is the steam pouring out of them onto your windscreen when you go through a puddle. I may have some experience of this 

One thing that really did improve LGT insulation was 10mm foil faced closed cell foam stuck all over the bulkhead, did noise and heat in one and is a LOT cooler, before you couldn't hold your hand on the tunnel, now it is just warm. 

[elbekko]

30 minutes ago, Bowie69 said:

You could duct it to push the air down and out the bay, but I do wonder why you would be suffering more than an old series with no heat protection at all? 

I wonder if that would actually be worse as there wouldn't be any air moving over the exhaust manifolds anymore.

[Bowie69]

14 minutes ago, elbekko said:

I wonder if that would actually be worse as there wouldn't be any air moving over the exhaust manifolds anymore.

True, though conversely it could be turbo charging the air into the bulkhead... 

[FridgeFreezer]

I know when other folks have done things like this before it can be very counter-intuitive as to what the air is going to do, adding speed holes can end up sucking air in rather than blowing it out for example... it's a job for little strands of wool and sticky tape.

I do agree with Bowie's experience though, a simple bit of bent tin over the exhaust where it gets near the bulkhead will likely give the single biggest reduction as the exhaust radiates a huge amount of heat directly at things, much more than the effect of some warm-ish air flowing around the place.

I'll also 2nd the experience with foil-backed foam, we did the transmission tunnel & under the middle of the seatbox on the ambulance and it knocked heat (and transmission noise) down significantly.

[Bowie69]

Oh, bear in mind small fans are noisy, if they aren't noisy, they aren't pushing any air, so don't get lured into the 'silent fan' offerings, they just turn really slowly and are equivalent of being coughed on by an asthmatic mouse. 

[landroversforever]

When our own Nige posted about this years back, he settled on an extra wing vent each side to help (I think it was an extra one each side, used on the wrong side).

Another vote for ceramic coating the manifolds. they'll be a big source of radiated heat.

[ThreePointFive]

This is why I'm glad we have this place. Many great ideas and people to tell you when you're wasting your time.

I did have an exhaust wrap when I had tubular headers on but I found the wrap made no difference. As I'm now using the cast manifolds, they seem like it would be a lot harder to wrap and not worth the lack of effect.

Ceramic was ridiculously expensive when I first looked at it, so perhaps it is worth another enquiry. I would look at doing the manifolds and the Y-pipe, after that it can be left plain.

I know the exhaust is the main source of under-bonnet heat but I can't help but feel the rad would be more effective if engine bay air was being actively drawn out rather than piling hot air on top of hot air, so not quite ready to rule out other ideas. It seems intuitive to me that if I'm trying to increase cooling, I need to draw in cold air and push out hot. I could put in a good size sucker fan on the top wing and pull that cold air across the engine to the passenger side vent, with a pusher fan there.

The PC fan thing is exaclty why I wanted to ask, I didn't even think of ATV/bike fans - they are far more effective for the same size. What they aren't, is cheap. But as it's not a case of a few quid to have a play (£75ish each fan) I can't justify a few degree C drop.

I'll make some calls about ceramic coating. It's good timing too, after only a year the paint on the manifolds is 90% rust.

[landroversforever]

Try Zircotec, there based in Abingdon Oxfordshire. Unless you've got somewhere closer of course.

Without cutting massive holes, I can't see any fans delivering that much in the way of engine bay heat loss. Other than when you've got it buried in mud, it will be letting heat out below. Have you got any of the temp stickers that @FridgeFreezer loves? see what the actual temps are getting to. 

[JohnnoK]

13 hours ago, ThreePointFive said:

This is why I'm glad we have this place. Many great ideas and people to tell you when you're wasting your time.

I did have an exhaust wrap when I had tubular headers on but I found the wrap made no difference. As I'm now using the cast manifolds, they seem like it would be a lot harder to wrap and not worth the lack of effect.

Ceramic was ridiculously expensive when I first looked at it, so perhaps it is worth another enquiry. I would look at doing the manifolds and the Y-pipe, after that it can be left plain.

I know the exhaust is the main source of under-bonnet heat but I can't help but feel the rad would be more effective if engine bay air was being actively drawn out rather than piling hot air on top of hot air, so not quite ready to rule out other ideas. It seems intuitive to me that if I'm trying to increase cooling, I need to draw in cold air and push out hot. I could put in a good size sucker fan on the top wing and pull that cold air across the engine to the passenger side vent, with a pusher fan there.

The PC fan thing is exaclty why I wanted to ask, I didn't even think of ATV/bike fans - they are far more effective for the same size. What they aren't, is cheap. But as it's not a case of a few quid to have a play (£75ish each fan) I can't justify a few degree C drop.

I'll make some calls about ceramic coating. It's good timing too, after only a year the paint on the manifolds is 90% rust.

Why not try a bike breaker's yard?

[ThreePointFive]

10 hours ago, landroversforever said:

Try Zircotec, there based in Abingdon Oxfordshire. Unless you've got somewhere closer of course.

Without cutting massive holes, I can't see any fans delivering that much in the way of engine bay heat loss. Other than when you've got it buried in mud, it will be letting heat out below. Have you got any of the temp stickers that @FridgeFreezer loves? see what the actual temps are getting to. 

I'll give them a shout. Yes I have got those, I need more. They're all reading around the 70-80 degree mark so not great, not terrible.

In terms of cooling, everything is doing its job, it's just about taking a few degrees out of the bulkhead so it doesn't get quite as sweaty in summer. I do think the exhaust is the next culprit but extracting hot air won't hurt.

10 minutes ago, JohnnoK said:

Why not try a bike breaker's yard?

There's a reasonable idea...

[elbekko]

14 minutes ago, ThreePointFive said:

it's just about taking a few degrees out of the bulkhead

Out of the box idea: put an offset skin over the bulkhead, a bit like a safari roof, and duct cold air through there, with a motorcycle fan.

[landroversforever]

I’d say getting rid/reducing the source should be no.1, then worry about extra fans if you still have an issue. 

Have you got any kind of shield on the bulkhead at all? The dimpled/pressed Ali shred work well for a bit of heat reflection, but cruicially an air gap. 

[Snagger]

On 5/31/2024 at 4:09 AM, FridgeFreezer said:

I think almost everything that got AC also got helper electric fans, Range Rovers definitely did (so I'd assume Disco did too), as did Freelanders - probably not an Aus thing as much as an AC thing as you're putting another heat exchanger in front of the stock rad.

Correct.  AC equipped Defenders had the twin electric fans too, hence the extended nose and grille.  I agree that an electric fan or two in front of the rad to boost the viscous fan when needed is the best bet.  Scoops on the wings are useless and PC fans won’t do a thing.

I think ceramic coating the exhaust manifolds and down pipes may help, and checking that the shroud for the viscous fan fits correctly to ensure fan efficiency is important.  Obviously, radiator condition is crucial - not just it being clean out side but referee from scale and rust internally and the fine fins not being bent and blocking airflow - that can become an increasing problem with old rads as the fins corrode and weaken.

[mat wilson]

Mines another vote for the foil backed foam on the bulkhead, I did as much of the bulkhead and tunnel I could on my 300 D1 and it made a noticeable difference to heat and noise, I just used the cheap stuff off eBay.

I would also create heat shields over the exhausts as that will make a huge difference if it doesn't have any.

The extra fans on air con models are to reject the heat from the Aircon system when stopped and idling as the viscous fan can't move enough air in that situation, Aircon systems don't create cold they remove heat.