Just returning to a previous topic, bonnet vents for the KJ, particularly the CRD. I ran across this photo on the KJCountry forum in the US, and the guy that posted it is from Russia!
Love the look of this work:
It just so happens that Whitworths Boating shops and their website carry these stainless steel vents and they are just $24 each here. Tempting, but I think he should have moved them forward a little. The stainless steel would look good on a silver KJ.
They seem to be right over the cross bracing in the bonnet, and you can't cut through that without risking the bonnet distorting. There are a number of threads on the LOST forum in the US about installing vents in the kJ bonnet (or hood to them). I would move them forward to avoid the cross bracing.
I'm curious, I might look into this further. I've been meaning to sort out excess heat for a while now. Got the tranny cooler but bonnet venting may also help. Anyone got it sorted yet?
I removed the insulation blanket today to get a look at the bracing. The insulation weighs abit. There are nine plastic rivets to remove to get it off but it's pretty easy, just use some sidecutters to lever up the centre circle of the rivet and the plastic post slides up and the whole thing can be removed. Leave the centre one to last so it will hold there while you remove the rest.
I have attached a photo of the underside of the bonnet, with the rear (firewall end) of the bonnet at the bottom of the photo. You can see by the cross bracing that there is very little space for vent installation that is not affected by the bracing. The longest open (unbraced) spaces are over the wheel bulges but these are compound curves and a hard place to put a vent and probably less effective than one perhaps just behind the fan shroud.
The yellow lines represent the outline of the Whitworths vents that the guy from Russia used. I now have a set of those as well. The base cutout required is 90mm by 300mm. The rear of the fan shroud is 39cm from the front edge of the bonnet. Using that as a reference point the yellow rectangle represents the logical place for the Whitworths vent to go, but as you can see it needs to cross the centre brace. The vent has a flange on it so cutting into the brace would be required to install it. The brace is only held to the bonnet metal there with urethane adhesive blobs, so it is feasible that the vent and flange could be bonded in that fashion as well with little or no loss of strength - a good metal bonding epoxy system might work better.
I have made up some cuttting templates and used my laser line drawer to grid up the underside of the bonnet in preparation for marking it out. I should point out I haven't cut anything yet and may not at all. A ran the KJ today without the insulation blanket and it resulted in a temperature drop when warm to just two notches above the 1/4 mark, a whole notch less than the usual operating temperature for today's sort of weather (24C).
So Glen If taking the thermal insulation dropped it that much, I wonder if a thinner insulation type material (possible a alloy heat tape) would protect the paintwork on the bonnet enough but allow a cooling effect.
Might save some holes cut in the bonnet
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Yeah Scotty I am going to leave the insulation off for the time being. After talking to another KJ owner tonight, who is trying to solve his heat when towing problem, I have decided to return the Whitworths vents. They are too deep and can't really be modified to clear the bracing; and importantly they are not easily painted (need to sand blast them at the very least, and that will cost as well). I need a surface vent where I can leave the brace as is and just cut out the skin. In the mean time I'll enjoy the sound of the engine.
Hi Glen..is that the only size vent they make? I was thinking that maybe a 200mm long vent would fit if you utilized the flat area between the cross brace and the windscreen end of the bonnet. Because of the upward sloping nature of the bonnet and placing the vents closer to the windscreen there would be no pocket of hot air trapped in the highest spot...and to my mind the blast from the fan would be removing heat from more of the motor than if they were further to the front[like the Ruski has his.
Yes they do make a 200mm long vent that has only three of the large lovers but same look. The problem with the location of the vent is that you want them to be in a relatively low pressure area of the bonnent so that air actually gets sucked out at speed. My mate Phil taped lengths of wool all over his KJ bonnent and went for a run to get an idea of the high and low pressure areas. There are several good articles on this subject, and you might find this an interesting read:
Placement nearer to the front (but behind the front leading edge) is actually in the low pressure area, so the higher pressure air hitting the front of the intercooler/radiator etc will exit the under bonnent area more effectively if the pressure differential is greatest, ie it will go out the lower pressure path. One of the articles above show a Chrysler design with pressure hitting the vehicle as different colours, and the area near the windscreen is the worst possible place for a vent as the air would actuallly be forced into the vent and engine compartment and may make the cooling system less effective than it is now.
In the photo below (taken from the last article listed above) the Red represents the highest pressure and the Purple represents the lowest. In terms of the pressure scale the highest to lowest pressure designation colours are: Red, orange, yellow, yellow/green, green, blue, purple. So the area in the first one-third of the bonnet is a desirable louver vent location for exhausting the high pressure air going into the front of the vehicle.
Those that remember my previous thread on this subject may recall that I bought a differential air pressure gauge (the Magnahelic shown) but I have not been able to plot the KJ yet because it's stuck in a storage unit in Sydney until I can get my shed to lock up state, but I still intend to do it someday.
Yes, I remember the posts from back then and what you show with the diagram is correct...for the outer skin of a moving vehicle. It's very much like the theory of lift, as applied to an aircraft wing, however it doesn't take into account the pressure under the bonnet caused by flow through the grill, plus what the fan creates. Years ago, I had a Fiat 124 Sports which had a bonnet profile very similar in shape to the KJ, but it was hinged at the front. On more than one occasion, the latch let go and that bonnet would ride up about30 cms and stay up until I slowed down and stopped...it would then settle back to its proper position.
I don't know about the fan on your machine, but mine blows like a hurricane and I suspect that all the moving air is forced towards the firewall and then deflected downwards because it has nowhere else to go.
Just thinking out loud.
What about that corrugated tubing they use for brake cooling.
Mount a length from the top of the engine bay to exit below the footwell, flattened out to create a venturi. This might suck out the hot air and send it under the car.
__________________ 2002 KJ 2.5Lt CRD minor mods sofar.
I had previously removed the rear engine bay / bonnet seal. It pushed warm air into the internal vent pickups so it wasn't going to be successful. I have recently repositioned it to be off centred toward the driver's side. This leaves a gap on the passenger side which doesn't coincide with internal vent pick ups. I know this is a high pressure air space. There may though be a small increase in airflow by finding gaps that won't cause internal issues and as well as reducing the bonnet insulation as Glen has done may in combination reduce engine bay heat sufficiently.
I returned the boat vents in the photos above, the collar was just too deep to enable mounting and there was no flex in them.
I have now received my new vents from Quadratec. These are made for the Wranglers but I thought they would work on the KJ. The photos below show them laid out on the KJ bonnent and I think they look good and suit the KJ. These vents are slightly curved so they follow the bonnent lines really well.
I have retrieved my differential air pressure gauge and will be doing the pressure measurements later this week once I have the hoses and fittings. More soon.
Hmmm...I do actually like the black but I will check the feasibility of painting them, anyone know where I can get spray cans of the KJ Silver (PS2 I think is the paint code ..but I could be mistaken)?
Yes, I remember the posts from back then and what you show with the diagram is correct...for the outer skin of a moving vehicle. It's very much like the theory of lift, as applied to an aircraft wing, however it doesn't take into account the pressure under the bonnet caused by flow through the grill, plus what the fan creates. Years ago, I had a Fiat 124 Sports which had a bonnet profile very similar in shape to the KJ, but it was hinged at the front. On more than one occasion, the latch let go and that bonnet would ride up about30 cms and stay up until I slowed down and stopped...it would then settle back to its proper position.
I don't know about the fan on your machine, but mine blows like a hurricane and I suspect that all the moving air is forced towards the firewall and then deflected downwards because it has nowhere else to go.
Coupla good considerations in the above post .... when contemplating the whole ... where do I rape my bonnet ... process.
Both - inner and outer pressures need to be taken into consideration. Its a bit pointless chopping holes where theres a high pressure zone on the underneath of the bonnet .... If theres a high pressure zone at the same location on the outside.
.... and outside pressures at some points change, depending on vehicle speed .... such as the rear, centre area of the bonnet e.g. where the two square vents are in the pics above by glend
Airflow under the vehicle assists with gearbox cooling. Losing flow volume via great big holes in the bonnet may not be an issue in environments where the gearbox is getting dragged thru 2" of snow .... but its something to consider in hotter climates.
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Hmmm...I do actually like the black but I will check the feasibility of painting them, anyone know where I can get spray cans of the KJ Silver (PS2 I think is the paint code ..but I could be mistaken)?
I know some paint wolesalers (who sell to the public) will mix colors and put into a spray can. BODYSHOP PAINT SUPPLIES GEELONG is the local, however they have stores elsewhere. Might be worth the Google.
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Bonnet Venting
2002 KJ 2.5Lt CRD minor mods sofar.
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