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MG MGA - Exhaust smell/leak in the passenger compartment.

Can I take my car to a regular "exhaust" shop to get a diagnosis or do I need an MG expert?
gerard hutchinson

Put it up on a hoist, run it up on ramps, or just get your head under, get someone to hold a bunch of rags over the exhaust end with the motor running at idle, and look, listen and feel where the leak is coming from. Do your own diagnosis. Save some money!
Barry Gannon

Shine a torch onto all the grommets on the bulkhead (firewall) from the engine side. Any light showing through shows leakage points.

Colin Manley


After you have done Colin's check on grommet holes have a look up in the top corner between the firewall and the body skin. There is usually a significant gap there, up to 1/4" wide. I plugged both corners and all my fume issues disappeared.

Steve Gyles

They leak between the manifold and the exhaust pipe.

Use a 3 ft long piece of hose to locate the leak. Seal it with silicone sealant.

Rinse and repeat.
A Bowie

@ A Bowie - Thanks for the advice, but please explain how does the 3 ft hose help me locate the leak?!

@ Steve Gyles - what did you use to plug the corners?
gerard hutchinson


I cannot remember now, too long ago. But some sort of mastic sealant would probably do. If I was doing mine again right now I would have a look round my garage to see what I had at hand - probably Plumbers Mate. Over here in the UK it's a sanitary jointing mastic that adheres to metal, paint, porcelain etc.

Steve Gyles

Gerard. Use the hose like a stethoscope. Listen at one end, poke around with the other.

I have had my car for over 7 years and I still havent managed to find all the gaps and holes in the bulkhead yet.
I recall using something called "Dumdum" paste (it has nothing at all to do with ammunition) to seal up the holes.
It is a very thick non-setting black paste that you just push it into the gaps and holes to fill them and it worked really well.

The biggest gap to that I found was along the entire top edge of the bulkhead, there was a 1/8" gap.

Even this week, I have just now found even more gaps at each corner of the heater unit where it goes through the scuttle.

I am so used the the MGAs fumes that, probably, if I manage to stop all the gaps and actually prevent all the engine fumes from getting into the cockpit, I won't like it! :-)


Colyn Firth

The fumes used to be very nasty in my car until I found those massive gaps in the curved corners of the firewall. I would have put my gaps at over a quarter of an inch at the widest. Sealing them totally cured all my fumes. IMO they were the greatest single source of fumes over and above all the firewall drilled holes.

Steve Gyles

Gerald, if I recall correctly, there was also the issue as to which direction the tailpipe is pointed.
If the tail pipe points upwards the exhaust fumes would come back into the cockpit more than if the tailpipe points towards the ground.
A clean running engine (not a oil burner,nor running too rich) will put out less smelly exhaust fumes.

Ray Ammeter

Thanks again gentleman.

Feeling around this weekend, I agree the gap at the top edge of the bulkhead must be the main problem. I used a "thermo" sheet material for the firewall, so many of the normal openings seem to be sealed. But the top edge clearly is not. And I am not at all sure what to use or how to reach the area. I'm not really looking forward to folding myself up to get under the dash. As always your suggestions are much appreciated!!
gerard hutchinson


The MGA exhaust *should* point upward, with the tip between one and two o'clock seen from the back of the car. Pointing it downwards causes all sorts of undesigned stresses in the exhaust system and leads to joint / mounting failures and fumes!

dominic clancy

Yes, it is very odd, but if you point the exhaust tip down and outward (7-o'clock) it will sometimes waft exhaust fumes up and over the rear body into the cockpit (when top is down). Pointing the exhaust tip toward 2-o'clock is correct and works well (just under the bumper facebar inboard of the overrider).

Correct orientation for the muffler (silencer) is with pipe at the bottom, main body straight up centered between leaf spring and fuel tank, and the outlet tip around 2-o'clock position. See attached picture.

Barney Gaylord

Dominic and Barney,
I just went out and looked at the tailpipe. On my car the tailpipe does point at the seven o'clock position. I recall I did this so the muffler would clear the gas tank by as much distance as possible. I will rotate it to the 2 o'clock position and enjoy a bit more fresh air.
I thought after a ride in an MG, one is supposed to smell like exhaust fumes. That was the experience I was after. Not really...Ha Ha.
Ray Ammeter

This thread was discussed between 28/02/2016 and 09/03/2016

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