Thread: Will a bonnet scoop reduce heat in the engine bay?

Originally Posted by gavinwibrow

Tell us more about the "vents out in traffic/crawling. Vents in and out bottom at freeway speeds."

Sounds like you might be onto something good.

At very slow speeds the fans blow hot air out of the bonnet scoop and also out of the bonnet side vents. Even when the fans are off you can see hot air escaping from the bonnet scoop

There are two holes cut under the bonnet scoop, at high speeds the air comes in and down each side of the engine and the Venturi effect would assist hot air escaping the engine bay by in effect assisting air to be sucked through the radiator and directing air down next to the engine and where the Exhausts go down.

Originally Posted by blackrangie

At very slow speeds the fans blow hot air out of the bonnet scoop and also out of the bonnet side vents. Even when the fans are off you can see hot air escaping from the bonnet scoop

There are two holes cut under the bonnet scoop, at high speeds the air comes in and down each side of the engine and the Venturi effect would assist hot air escaping the engine bay by in effect assisting air to be sucked through the radiator and directing air down next to the engine and where the Exhausts go down.

By fans I assume you mean the radiator fans, not extra fans built in?

I'm sure any hole in the bonnet will pass air,, our D2 will need one at the very front to catch any incoming air as the whole top part is a dead air zone,, I reckon the side vents are worth a look though,,,,

Originally Posted by gavinwibrow

By fans I assume you mean the radiator fans, not extra fans built in?

Twin thermo rad fans + twin condenser fans.

Then 2 spals above twin coolers on frame a few inches behind bash plate

Originally Posted by Pedro_The_Swift

I'm sure any hole in the bonnet will pass air,, our D2 will need one at the very front to catch any incoming air as the whole top part is a dead air zone,, I reckon the side vents are worth a look though,,,,

Thesw scoops are avail to suit D2 i believe.

man, that is sexy looking vehicle

I think the idea is to cause the air to be sucked through the radiator to increase cooling. To do that you need to vent hot air from behind the engine to create a vacuum to cause the air to be sucked through the radiator. That requires a rear facing vent or vents so the air goes either towards the windscreen or out the side vents, as on Range Rovers.
A forward facing vent could prevent that happening because the air it took in would not go through the radiator, but would go into the engine bay. So a forward facing vent might not increase cooling. In fact, if the air thru the vent cooled the engine air it might reduce the venting and vacuum effect.
Better to make it easier for hot air to vent near the firewall, I think.
Anyway, I'm no expert, but that's what I've picked up from others who seem to know their stuff.

Originally Posted by DiscoMick

.... So a forward facing vent might not increase cooling. In fact, if the air thru the vent cooled the engine air it might reduce the venting and vacuum effect.
.....

It should .. depends on it's design.
I've relayed a story before where my '79RRC started running hotter once when out Uluru way, coming home ... where the temp gauge was just on the red zone(normally at half way).
After trying everything else I could(basically thermostat), it wouldn't run cool.
So as a last resort I found a strong cardboard box in a bin at a wayside stop, placed it under bonnet and ran with the bonnet half up(about 6 inches or so) tied down with some coathanger wire.

temp dropped significantly, and in fact had hardly any heat in the hoses. Ran like that to about Marla, where it started raining, and I pulled the box and closed the bonnet. Kept the box in the back .. just in case.

Popped bonnet could equate to a large forward facing vent, to direct cooler air over the engine.