Its winter.. lower mpg expected ?

[Agreeable Slick]

i looked in the vw manual in the glove box and it says that your fuel consumption is double until the cat is up to temperature and it takes approximately 4 km of driving to warm it up.

perhaps its just taking longer to get the temperature in the cat. since reading that i never accelerate hard until i can see the water temp gauge start to move. and it doesnt budge for longer during these cold morning we have been getting.

That doesn't make sense, why would the CAT have any effect on fuel economy? It would obviously have a massive difference on emissions but I can't see what the CAT would have to do with fueling?

Fuel can be used to help the light off process in the cat, and prevent too much damage to it. I.E. there is sometimes an injection of fuel on the exhaust stroke hence the increased use of fuel until it's up to temp.

[Little Legs]

i looked in the vw manual in the glove box and it says that your fuel consumption is double until the cat is up to temperature and it takes approximately 4 km of driving to warm it up.

perhaps its just taking longer to get the temperature in the cat. since reading that i never accelerate hard until i can see the water temp gauge start to move. and it doesnt budge for longer during these cold morning we have been getting.

That doesn't make sense, why would the CAT have any effect on fuel economy? It would obviously have a massive difference on emissions but I can't see what the CAT would have to do with fueling?

Fuel can be used to help the light off process in the cat, and prevent too much damage to it. I.E. there is sometimes an injection of fuel on the exhaust stroke hence the increased use of fuel until it's up to temp.

Unburnt fuel in a CAT is bad news for its health as you say, so running richer is not desirable - richer when cold yes, richer for the health of the CAT when cold - doesn't sound right to me.

[Agreeable Slick]

Sorry I worded that badly it's like this.

Running rich = higher/hotter exhaust temps, an late post injection of fuel into the exhaust cools exhaust temps, which helps cool the gases entering both the turbo and cat. This prevents temperature fatigue cracks in both the metals of the turbo and the materials in the cat until they are up to a reasonably temp in which case the post injection map tends to switch over.

[Little Legs]

Sorry I worded that badly it's like this.

Running rich = higher/hotter exhaust temps, an late post injection of fuel into the exhaust cools exhaust temps, which helps cool the gases entering both the turbo and cat. This prevents temperature fatigue cracks in both the metals of the turbo and the materials in the cat until they are up to a reasonably temp in which case the post injection map tends to switch over.

I always thought running richer gave lower/cooler exhaust temps and leaner gave higher/hotter exhaust temps, infact some high perfomance engines run rich specifically to cool?

[Agreeable Slick]

Remember we are talking about initial start up and complete combustion. Sticking unburnt and non combusted fuel in to the cylinder will lower burning temps.