Topic

Hi guy’s, my first post, let’s see if I can get this right, if I bugger it up and get it wrong it won’t be a surprise, to me anyway!
Question: can a slightly leaking head gasket cause emissions to be high, I fitted a stainless steel sport cat from Rimmer Bros last year, I’ve done 9,000 miles with it and this year it just failed (0.420)
Car is also due a service
I thought after shelling out £500 I’d be ok for a while, I’m getting on average 390 / 430 miles per tank of E5, what’s your thoughts.

G’day and welcome, as far as your posting skills go…….so far so good!
A slightly leaking head gasket is much like slightly pregnant …….. before you worry about emissions you need to fix this issue first!
Mind you a totally buggered and blown engine will produce 0% emissions
It would depend upon how and wher the head gasket failed as to if it would sffect emissions…….. an oil leak into the combustion chamber would, as would a combustion leaking into a neighbouring cylinder, water leaking in would too, to la lesser extent

Is this the first MOT since fitting the sports cat ?

After market cat's often need a good heating to get them to work, ideally a good run down a motorway then straight to the MOT tester, hopefully he will test immediately. It's a well known problem with most non OE ones not only for MGF/TF but all cars, possibly due to less precious metals in them

I would agree with that, especially if there have been contaminants through.
Earlier this year whilst doing a job which involved removing the breather pipes of the cam cover, I got them the wrong way about on reassembly.
This stupid error drew oil from the sump into the combustion chamber & I had clouds of white smoke belching out of the exhausts & that through a new cat’.
With this cat’ I was sure I would have eliminated any MOT pass chances. However I ran it really hot over several days once the fault was recognised & corrected, slowly the smoke diminished until no sign of it could be seen, then after another hot run (not easy in traffic where I live) I chucked it at the MOT station & it passed.
Take heart & run it hot for a bit but do watch your nearly pregnant gasket.
M

More importantly get a low coolant alarm if not already fitted before you drive it much more, you can buy various kits or make your own from circa £25 upwards.

180Pete,
Honestly your post causes me stress on the leaking head gasket, you have three contained systems,

Oilways, Could be leaking out or internally = medium risk leading to total failure if not backfilled with oil
Coolant, Could be leaking out or internally = high risk leading to total failure if not back filled with coolant
Combustion chamber, Could be leaking on combustion = bad and will get progressively worse

The combustion chamber leak could interfere with the emissions
The oil leak into combustion chamber could interfere with the emissions but you'd also get savage oil blow back if the engine is vent into the oil chambers
The coolant into the combustion chamber would definitely cause emissions failure but you'd see a pressurized coolant system and smoke from the exhaust.

The very knowledgeable people on here really need a bit more info to help you.

But a starting point would definitely be the head gasket

Hi notanumber, yes it’s the first mot since fitting it, have done about 9000 miles, it doesn’t use any oil and I only top the coolant occasionally 👍

P.S. Thanks to all who gave input, think we’ll just bite the bullet and strip it down 👍