Re: The air vents on the lower rear of the front doors
Posted: 05 Jun 2013, 22:09
Too dark for me to look now, but heres my thoughts. As said, I have a Caravelle with the interior roof vents and I can only assume that the system works like this:
Behind the dash there is a horizontal piece of trunking which as well as providing strength to the front end is vented and this air enters the trunking, then the front doors through the hole between the hinges, through the door (taking some air from the door vent if slid to the open position), into the B pillar where it then goes straight upwards, along the channel in the sides of the roof (ie above sliding door inside).
On Caravelles the additional four roof vents also enter this channel. On other models the air just continues on at which point there can be nowhere else for it to go except the rear exterior grills at the back (unless it exits by some other route I have yet to discover. It would seem to add up since no exit would produce no throughflow.
Earlier Aircooled engines may well have had some benefit from those rear grills (although I suspect not much at all) but I think in the later WBX models these vents found far more use for letting hot air OUT rather than sucking cold air IN and effectively operate in reverse. How else would heat in the upper part of the engine bay escape?
VW went to great lengths to split the engine (top and bottom) using tinware and a well fitting rubber seal (on Aircooled models even the sparkplug lead holes are sealed to avoid cooling air leakage). On the WBX Most of the heat from the engine is from the exhaust and associated pipework which is underneath. When the vehicle is in motion, the heat in the top of the engine bay has nowhere to go but up and out of those rear vents. Heat from below tends to work its way under the rear arches and through the grill in the rear apron (remember that?) as I've felt around after long runs and you can feel all that heat via those points.
That would seem to be how it works. As I say, Aircooled models are somewhat different although the engine bay is (normally) just as well sealed top and bottom and does have an air ram effect above the gearbox to assist with the cool air intake through the tinware ducting.
As an aside, T25s used in hot countries also tended to have the vented rear windows to mininise the parked-oven effect as well as encourage hot air out whilst travelling.
VW seemed to have concentrated their efforts on a free flow of air rather than 'scooping' it up and were well versed in using body cavities to move hot or cold air around even in the Beetle. The T25 is after all, an extension of all that heritage.
Behind the dash there is a horizontal piece of trunking which as well as providing strength to the front end is vented and this air enters the trunking, then the front doors through the hole between the hinges, through the door (taking some air from the door vent if slid to the open position), into the B pillar where it then goes straight upwards, along the channel in the sides of the roof (ie above sliding door inside).
On Caravelles the additional four roof vents also enter this channel. On other models the air just continues on at which point there can be nowhere else for it to go except the rear exterior grills at the back (unless it exits by some other route I have yet to discover. It would seem to add up since no exit would produce no throughflow.
Earlier Aircooled engines may well have had some benefit from those rear grills (although I suspect not much at all) but I think in the later WBX models these vents found far more use for letting hot air OUT rather than sucking cold air IN and effectively operate in reverse. How else would heat in the upper part of the engine bay escape?
VW went to great lengths to split the engine (top and bottom) using tinware and a well fitting rubber seal (on Aircooled models even the sparkplug lead holes are sealed to avoid cooling air leakage). On the WBX Most of the heat from the engine is from the exhaust and associated pipework which is underneath. When the vehicle is in motion, the heat in the top of the engine bay has nowhere to go but up and out of those rear vents. Heat from below tends to work its way under the rear arches and through the grill in the rear apron (remember that?) as I've felt around after long runs and you can feel all that heat via those points.
That would seem to be how it works. As I say, Aircooled models are somewhat different although the engine bay is (normally) just as well sealed top and bottom and does have an air ram effect above the gearbox to assist with the cool air intake through the tinware ducting.
As an aside, T25s used in hot countries also tended to have the vented rear windows to mininise the parked-oven effect as well as encourage hot air out whilst travelling.
VW seemed to have concentrated their efforts on a free flow of air rather than 'scooping' it up and were well versed in using body cavities to move hot or cold air around even in the Beetle. The T25 is after all, an extension of all that heritage.
