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Fumes in the cabin

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by Goldy » Sat Aug 26, 2017 6:41 am


noticed that my Mk3 is very fumey in the cabin to the point of giving me a headache. I can't see any obvious signs from extractor gaskets, and tends to be worse with the windows open. Im not sure if any of you have had similar issues ?

cheers - Nick
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by dinofritz » Thu Sep 14, 2017 11:12 pm

Hi Nick,

There's several areas where fumes from the engine bay can trickle in. Here are some of the more obvious ones to test one by one (through trial and error):
- in the engine bay, rear firewall, on top of the box housing the evaporator there is a small panel which is covered in closed cell neoprene rubber (heat insulation), but this also seals the zone between the engine bay and the fresh air vent at the base of the windscreen. If air can flow through this area, you'll get engine bay heat (and smells / fumes) sneaking into your fresh air system. To test, use duct tape to create a temporary seal and see if this cures the problem.
- if the bonnet seal is perishing, or your bonnet doesn't seal correctly, engine bay heat can sneak out of the leading edge near the base of your windscreen and into the fresh air vent, into the cabin again. To test, close the bonnet, then duct tape the rear edge to the body.
- final test, the footwell ducts at the front of the centre console have heatproof shielding both inside the duct itself and outside (at the base of the firewall). If these are perished, they let in a tremendous amount of heat, plus there are holes in them that can also let in fumes. I drove a Mk III where most of the firewall insulation had perished with age, and on a 40 degree day, wearing leather shoes, I thought my feet were burning. So if you're not experiencing this sensation in hot weather, this area may be okay.

Good luck troubleshooting,

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by Goldy » Fri Sep 15, 2017 1:36 am


Many thanks for your advice, I will systematically work through your suggestions this weekend.

Cheers !
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by Goldy » Wed Apr 18, 2018 9:43 pm

So the journey continues, my exhaust headers were wrapped which meant that although they were intended to keep the heat down, they also did not allow for the pipes to lose heat which over time caused them to calcify, and become brittle and crack. There was no choice but to start again, I had some new extractors custom made and then ceramic coated inside and out. It took some time but Im really happy with the result. It certainly helped but unfortunately there were still fumes there. I also noticed that there was oil coming out of the rocker breather which i initially thought was a faulty PCV but it turned out to be worse. At this stage it looks like valve stem seals, which I had a hint due to the smoke the car sometimes made at startup. The heads are off and I should find out in the next day or two...
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