Excessive CO at Idle

Very often after the fast idle and drop to natural idle, the CO can shoot up and then drop down. The emission tester (machine) moves onto the next stage once it has seen a pass (0.3). Had it not moved on automatically the stabilised CO could well have been much lower.

Graham

Simon Dean wrote in news: snipped-for-privacy@individual.net:

Could be the thermostat needs replaced, as in it's fully open all the time, more noticable at this time of year due to all that cold air going over the radiator, which will be at full efficiency if it has just been replaced ;-) and as for the noise, might just be a heat stove heat shield etc. rattling, or you may have a split in an intake pipe.

Hrm. I know my engine is very rattly. Someone once told me the camshaft and rockers need replacing. The exhaust itself... there's no leaking, the noise I notice, is coming from the tail pipe itself! Hand over the end for a few seconds reveals no nasties and the noise stops.

I think you might be right about the thermostat. IIRC, it's supposed to stay closed or whatever until the engine is up to temperature... so it should get hot, even it this weather.

I guess a thermostat can let go by over heating or something, like, if all the water floods out of the cooling system because the radiator inlet pipe shatters?

Could I also be right in thinking, that if the engine is not up to temperature, that could cause fuel consumption to increase?

Just some thoughts. Don't know if true.

Thanks Simon

The thermostat in my wife's 1600 Skoda let go in the summer. It failed closed. Took a roadside rescue to trace that one. On the plus side, I was attentive enough that I didn't cook anything. Skoda ones snap and clog up the return. I've not experienced any others. The car was fine with it removed (yes I bothered to put a new one in). Without it, nothing I did would persuade the temperature needle to move off the bottom. This included a stop start traffic jam on a hot day.

Warwick

Correct. As it is at a lower temperature it will cause the engine to think it is 'not warm enough' and run it at a richer mixture. Hence increase fuel economy. Obviously this would not apply if it were a diesel.