Exhaust fumes

[OlafR]

Good afternoon!

Despite the fact that my 1972 P5B Coupé is in overall good shape/condition, one thing really annoys me: After some 10mins driving with the front window(s) rolled down I am presented with not only a bit of smell (which I enjoy) but rather a wave of exhaust fumes. I have had the car thoroughly examined, but my mechanic doesn't have an idea.

Now, from a logic standpoint, I don't see all too many possibilities for the fumes to make it into the car; again, this only happens when the windows are open! Which leaves me wondering as to what might be happening? Only thing I (motoring-wise clueless) can imagine is that something (carburetors?) could be leaky. But considering the fact that two mechanics were at loss - where should I start?

Cheers,
Olaf

[lagain]

I have also noticed this from time to time, perhaps the shape of the car draws fumes from the rear.
I find that my car has far less wind noise on a still day, so when it is windy any thing could be happening !

You could also check your boot seal as fumes can be drawn into the boot and then into the cabin. If the window is open there is no cabin pressure to keep the fumes out. A few years ago when I went to Scotland I had luggage in the boot, including pillows !
When my head rested on them I was overcome by the stink. A new boot seal from Scotts solved that one.

[Simon H]

With the windows open I get what I can only describe as a 'burned hydrocarbon' smell. It's not exhaust fumes, more like crank case emissions or something similar. I have fitted new flame traps and made sure the breather pipes go where they should. The joys of driving old cars...

[enigmas]

If the crankcase ventilation system is functioning correctly, any crankcase fumes are (should be) ingested within the engine during the combustion process. A proper (modern) PCV valve plumbed to the inlet manifold then to the rocker cover would cure this issue...if it is the issue? More than likely though, there's a fair probably a weeping rocker cover gasket (at the rear) is allowing oil to run onto the exhaust manifold or engine exhaust pipe. Similarly, if the rear main engine seal or the rear gearbox seal is past it's best, oil will find it's way onto an exhaust pipe.

[ray]

I think you'll find Lagain has the answer. I have noticed this over the 28 years I have had my P5b Coupe. Fumes are collected in the boot if the seal is not good. With side windows open there can be reduced air pressure in the cabin ..or swirling air and this draws fumes from the boot, which has taken fumes from the rear of the car, where the exhaust swirls behind the car. We all know how the boot lid gets a bloom, along with the rear bumper. This is all from the cars exhaust. A new boot-lid seal stopped the smells in my car. You can test the seal by sliding a stiff piece of paper along the seal line, you may find 'almost' no contact in some places with the boot-lid shut.

[Warwick]

Jul 24, 2017 10:17:51 GMT @dicky said:

... The old boy's been gone 10 years now and was 93 when he died but he could improvise/mend/sort/think about most mechanical problems. He started driving in 1931  

Sounds like my Dad, Richard. And the same age. He's been gone 3.5 years, and would have been 103 now.

[Deleted]

I love quiet cars and over the years have renewed grommets and seals all over the place to stop noise creeping into the cabin. A while back I took out the back seats to fix faulty top shock absorber mounts and replaced the foam tucked up inside the rear door posts and which are presumably there to cut down noise and stop fumes from the boot.I'm sure air can get through this into the cabin carrying fumes from the exhaust and boot area.
I do love that old car smell on opening the doors of the coupe,old leather,old wax and varnish with a hint of old oil.Anyone who could make it in aerosol form would be on to a winner.

[OlafR]

Thanks guys, your thoughts are very much appreciated!

The boot lid seals are pretty good (they look quite new). I haven't ever smelled anything in the boot either. I'll try the stiff paper test though.
The rear gearbox seal has just been replaced, so that should be fine too.

The door seals must have been replaced no all too long ago as well. The LHD back door's seal though is very stiff, I shall replace that one soon.

Now regarding checking the crankcase ventilation I'm afraid my technical knowledge won't be sufficient. :-(

I'm wondering whether I shouldn't invest some £40 for a smoke machine to check for any leaks?

Cheers,
Olaf

[ozriderp5]

I had bad exhaust fumes in mine when I got it, everything looked fine in the engine bay and underneath.

I ended up getting under the car and running my hands the length of the exhaust looking for holes, unfortunately I didn't have to go far before I had black sooty hands.


A 'new' tail section had some real dodgy welds that had holes everywhere. They were only small but still enough for fumes to be exiting under the car.

Patched them and no more fumes.

[djm16]

There is a very easy way of checking for exhaust leaks.

If you have a willing wife, just get her to block off the tailpipe with her hand (in a leather glove). The sound of exhaust escaping a hole will be very loud. In the absence of a wife, duct tape a rubber kitchen glove over the tail pipe instead.

[Eric R]

or a potato cut in half and wedged over the tail pipe which worked wonders when I was a teen and wanted to cause mischief!

[Colin McA]

Would altering the tail pipes help.

Range Rovers and land rovers angle the tail pipe rather than go straight. There are probably avoiding the rear chassis crossmember but it might help.

You can buy pipe finishers that angle down and to the side quite cheaply something I have thought about fitting.

[Warwick]

If you're really serious, you could see if these are available for hire.
(Read the last sentence of the last paragraph).
www.amprobe.com/amprobe/auen/hvac-tools/ultrasonic-leak/amp-tmuld-300.htm?pid=73418

Or, if you're not that serious, you could try the method that Land-Rover used on the production line for the Series 1, 2, and 3. Wind up the windows, close all vents, and shut the doors after releasing a canary inside. If the bird escapes, send the vehicle back down the line and check all the seals.

[OlafR]

(Sorry for responding so late, still being drowning work-load-wise!)

Yes, I am serious, the car will go to the workshop for another checkup tomorrow. I'm not all too confident that they'll find anything, but I'll be going on a little travel with my son starting September 8th (London, Goodwood, Birmingham, the rest is open - we have around 10 days worth of time), so I thought it would make sense to have the car thoroughly checked in advance. We'll see if they find anything (they haven't last time).

I suppose I'll have to take it from there, provided that they don't find anything. At least the car will come back "home" for a week, and I'll see a few people that might even come up with ideas. Seeing the car might help, that's for sure.

Cheers,
Olaf

[Warwick]

Good luck finding it.

[Jens Munk]

Mine has the same problem with exhaust fumes with windows open, and the first time I posted my grief, the answer was the boot seal. I replaced this but the problem remained. However, I have just spotted how the fumes get in. They get in through the battery box.

While the box itself is (over) made of solid British steel, there is a giant hole in the bottom they will handle an exploded battery, but also allow the fumes in if it wasn't for a proper seal. The seal is not good in mine and in addition there is a big hole for the cable. Just tried to plug the big hole with a old towel and no more fumes.

I am amazed.....

Jens.

[frans]

I am experiencing the same problem. I have replaced the boot seal without change. But I also suspect that the smell comes from the the worn bonnet rear seal. Imagine that the fumes on the engine bay comes through the rear bonnet right into the fresh air inlet of the ventilation openings just underneath the windscreen! Anyway, I will replace the Bonnet rear seal and further investigate. Jens's hint of battery tray is also very interesting! Please, everyone, stay on this topic because my wife refuses to ride with me with the Rover unless I have fixed this problem - just to make sure sure you understand my problem....

[Jens Munk]

You could let your wife drive it. My wife loves driving the Rover

In case of the V8 engine, there shouldn't be any fumes escaping under the bonnet at all. Air is drawn from the air cleaner box into the rear end of the engine block and drawn out again through the two hoses on the valve covers and into the carburettors. It's a closed system. In addition there is gale force winds through the engine compartment effective blowing any leaked fumes out under the car and away.

The fresh air inlet theory is easy to test. Just close it by putting both vent and heating controls to their topmost positions.

May 14, 2018 20:11:14 GMT frans said:

I am experiencing the same problem. I have replaced the boot seal without change. But I also suspect that the smell comes from the the worn bonnet rear seal. Imagine that the fumes on the engine bay comes through the rear bonnet right into the fresh air inlet of the ventilation openings just underneath the windscreen! Anyway, I will replace the Bonnet rear seal and further investigate. Jens's hint of battery tray is also very interesting! Please, everyone, stay on this topic because my wife refuses to ride with me with the Rover unless I have fixed this problem - just to make sure sure you understand my problem....

[frans]

My wife prefers the Moggy convertible with fresh air until we fix the smelling issue!

[enigmas]

Interestiing read about the vexed issue of exhaust fumes and what causes them to be drawn into the car's interior. Having said that I've never experienced it in my coupe. The issue can also be caused by having the rear exhaust pipe not extend far enough away from the rear of the car. The vertical drop of the boot (like any car with this configuration) causes a negative pressure area at the rear of the car (whilst moving forward) that draws fumes back. If the boot seal is 'compromised' fumes are drawn past it.

Simply moving/angling the rear exhaust outlet to a rear side exit will eliminate the issue even if the boot seal is poor.

* Jens my car has twin exhaust outlets, one on either rear corner of my coupe and no fumes are drawn into the vehicle's interior despite one exhaust outlet being in relatively close proximity to the trunk mounted battery vent.




NB.
To test the boot seal cut strips of computer paper and place them between the boot seal and the sealing surface. If the seal is effective the paper strips will not be able to be withdrawn easily. If the strips pull through with ease the seal is not effective at that point.

[frans]

Enigmas, your advice to test the gap of the boot seal is super! Even though I replaced the boot seal and adjusted the boot lock, I still smelled the exhaust fumes. So I did the paper sheet test: the paper went through without any resistance! Then I noticed the two rubber stoppers on each side of the boot bottom! I adjusted them properly and first and preliminary result is: paper sheet can only be pulled though with resistance and the first drive no exhaust fumes!

[Jens Munk]

Frans,

Very good to hear that it was the boot seal leaking and an adjustment fixed it. Hope your wife appreciates it.

Enigmas,

The battery vent itself is what it is. The problem was that the seal to the battery box was bad and that there was no seal around the cable going though the side of the box.

Jens.

[Steed]

All good advice regards an oft recanted problem. 

There are also the small holes in the front under-dash. The cable grommets and gaiter( on steering column) tend to be disintegrated, however small there is a channel here for fume entry.

Andy

[brian66]

Just been looking at my p5b and noticed the rubber seal at the back of the bonnet was not located correctly so any fumes from the engine exit the rear of the bonnet straight into the air vent!