Bonnet Vents

[Guest robinj66]

I'm probably wrong but i think it's the fact that once the air has come through the rad and into the engine compartment, it has to get out again or it will fight against the "new" flow of air coming through the rad. Effectively it will slow down the flow of air through the radiator which doesn'thelp to maximise cooling. vents in the bonnet and sidewall allow the air to escape from the engine compartment, making room for new air to come in.

[Guest chris brown]

I've been following this thread with interest, because I don't understand how bonnet vents can make such a difference to cooling. By cooling, I guess we mean airflow through the radiator. Given that any air through the rad has to come through the grille, and this has a much smaller area than the open bottom of the engine bay, isn't it the inlet grille area that limits airflow, rather than 'outlet' away from engine compartment? Couldn't bottom of engine bay be partially covered to use venturi effect of higher speed/lower pressure air under car to aid cooling? Brian

You would be surprised how much pressure builds up in the engine bay just try driving with the gear stick gaiter off and see how much hot air blasts up the hole. Extra vents really do make a difference.

[Guest salty_monk]

Made a big difference on mine.

The black one I have now has the front infill panels behind the wishbones flared on the back edge to allow air to escape once past the rad.

 

I cut mine by drilling a big hole & running a hacksaw blade in a single ended holder along it & then used a file on the final bits....

 

Dan

[Guest charlie]

I've been following this thread with interest, because I don't understand how bonnet vents can make such a difference to cooling. By cooling, I guess we mean airflow through the radiator. Given that any air through the rad has to come through the grille, and this has a much smaller area than the open bottom of the engine bay, isn't it the inlet grille area that limits airflow, rather than 'outlet' away from engine compartment? Couldn't bottom of engine bay be partially covered to use venturi effect of higher speed/lower pressure air under car to aid cooling? Brian

 

I have just arranged for 2x vent pannels 10 vents in each out of alluminium one for each side of the bonnet to

match the Hood variety on the top of the bonnet, my reasoning is that good airflow past the rad/engine is important what goes in must get out,

and if you saw your temp gauge going rapidly north in heavy traffic on the M25 as i did, you will use any means available to keep the temp down inc 2x electric fans.which at tick over has dropped by 20 deg.so i hope i`m on a winner!

Charlie,

[Guest keith12]

I've been following this thread with interest, because I don't understand how bonnet vents can make such a difference to cooling. By cooling, I guess we mean airflow through the radiator. Given that any air through the rad has to come through the grille, and this has a much smaller area than the open bottom of the engine bay, isn't it the inlet grille area that limits airflow, rather than 'outlet' away from engine compartment? Couldn't bottom of engine bay be partially covered to use venturi effect of higher speed/lower pressure air under car to aid cooling? Brian

As with all the comments made about this issue the reason behind me venting is to release heat from under the bonnet after it has been pushed through the rad.

I have blocked off the gaps between the bonnet and the bulkhead as much as i can to try and keep the heat out of the cockpit during the summer LOL so creating more pressure under the bonnet, going back to a previous comment my gearstick gaiter is not fixed down at the moment and the heat blowing through from the engine bay is amazing but quite nice in the colder weather and when the 16 inch electric fan kicks in its like turning on a large hot hair dryer.