Exhaust fumes again

[Jens Munk]

Hey there...

I am again working on exhaust fumes getting into the passenger compartment when the windows are rolled down. It has been addressed here before, roverp5.proboards.com/thread/10338/exhaust-fumes , and I did get it fixed then. The problem is that the open windows creates a vacuum and fumes gets via leaks into the boot and from there into the rest of the car. I had already replaced the boot seal and the problem proved to be the seal on the battery box.

Well, the problem has slowly but steadily come back, but a look at the boot lid after driving some dusty roads revealed the culprit, which was also confirmed with a strip of paper.

It appeared that the glue had lost its grip on this section of the seal allowing it to tilt enough to leave a small gap. Applying some super glue fixed it - almost. It is almost there, but high speeds and windows rolled half down can still leave a hint in my sensitive nose.

So all the above and past posts have been about fumes getting into the boot, but another issue is how it gets from the booth and into the passenger compartment. Here I note that there is essentially free access over the wheel arches. A lot of rust repairs have been made on my car in the past, and in one side there is a piece of metal spot welded in, but not sealed, and in the other side this is missing completely.

Any suggestions on these openings between the boot and passenger area?

[enigmas]

Jens the boot lid by virtue of it's shape (P5s aren't exactly aerodynamic) creates a low pressure area at the rear of the car when moving forward. If the boot seal is compromised or there are open holes in the boot floor (missing grommets) then exhaust fumes will naturally be drawn in. The battery clamp down lid can be fitted with a thin adhesive rubber strip seal where it meets the lower portion of the case it locks onto. Note that the battery box is fitted with a large vent tube underneath. This is to vent any hydrogen gas that may be released by the battery whilst charging.

* If you can pull a strip of computer paper from between the closed boot lid and the boot seal at any point it's obvious that the seal is ineffective.

On both of my classic cars (P5 & MG Magnette) I fit a 3 ply panel tailored to cover the full area where the rear seat backrest fits. I also use duct tape to seal any openings the panel won't conform to. Similarly the rear parcel shelf is virtually hermetically sealed. This also assists in noise reduction and insulation to the interior. Opening any of the interior windows front or rear does not induce fumes to enter the interior.

If your car has no obvious exhaust leaks underneath and you pay attention to any openings you may have missed at the rear of the car, it should be exhaust fume clear.

[Phil Nottingham]

There is open access to both sides of the boot above the arches to the area behind the D post trims, You can see the from inside the boot behind the boot back board

[lagain]

I think that they are drawn back over the car. If you look at a light coloured P5 with older paint the area of the boot lid above the exhaust pipes has yellowed. I clean that area of my car and the bumper every time I get home from a run, but it is still slightly noticeable. You would think that as you went along the fumes would just wizz out behind you and disappear, but presumably not.

[joffa]

Jens, although it does not directly address your question My P5B Coupe has the same issues (at least when my car was on the road as is I have been delayed putting the engine back together).  Mine has rust repairs above the wheel arch as well that has left air gaps and the rear parcel shelf is also pretty much open.  Something I have wondered about when trying to fix this is how far behind the car does the exhaust gas swirl before being sucked forward into the boot area due to the low pressure zone that exists from the boot surface to some distance extending out from it.  I also assume that distance changes depending on the speed.  I was wondering if I extended my exhaust pipe that at some point the exhaust would swirl and curve up behind the car but not be sucked into it?  My exhaust is currently about 2" towards the front of the car from the bumper so I think is a bit shorter than factory but I think extending the exhaust tips would have to go some way to fix or reduce the issue. To fix it completely, would it be a few inches past the bumper or a few feet? - be a good experiment.  When mine is running again I might jam on a pipe and see what lengths reduce the smell at certain speeds but I wish I could afford a few hours in a wind tunnel to test it.  Perhaps even one of those American style pointy down style exhaust tips may deflect the gas down and before it gets a chance to be sucked back into the boot lip?