Cleaning Engine (2.0 TFSI) after running rich

[sammy.se]

Hi,

My petrol 2008 A4 2.0 TFSI has a thermostat stuck open, and doesn't get up to temp (90 degrees) unless I'm stuck in traffic or going slow.

It's booked in for a repair on Monday, so hopefully that will fix things. I will also ask for spark plugs to be replaced on the basis of the rich mixture affecting them.

My question is, since it's been running rich, should I clean the engine somehow? What do people think about those additives like redex?
Or, should I just forget about it and not doing anything after the repair?

No fault codes are coming up, so everything is fine apart from the engine running cool.

EDIT: I am *assuming* that the engine is running rich, because it's cool - rather than a fault code telling me it's running rich. I still want to get the thermostat fixed either way.

Thanks!!
S

[Steven715]

Hello,
It’s my understanding that once the lambda sensor warms up in the exhaust it will put the fuel system into closed loop the engine will run at its normal stoichiometric program yes the engine will use more fuel as it’s less efficient at cooler temperatures but it will still be running normally.

My suggestion is once the thermostat is replaced give the engine a good hard run to clear anything out.
I strongly suspect that your spark plugs will still show a normal colour if you you replace the doesn’t hurt to have a look.
A fuel additive won’t hurt anything either it will clean your injectors out and some carbon deposits that will be present is a normal happy running engine.

Alternatively you can run a tank of premium fuel such as shell super unleaded or BP ultimate for example.

I hope this puts your mind at rest.

All the best.
Steve.


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[Crasher]

I would recommend an oil and filter change as the oil may be contaminated. Mrs Crashers Polo did the same thing on a long drive home and when I did the thermostat I changed the oil just in case. As for the rest of it, hopefully the lambda sensor will burn clean and the cat but there is always the potential for long term damage to these parts as happened on my Octavia when the thermostat stuck open, a few weeks later the cat started rattling as it was breaking up inside.

[Steven715]

Very good advice there


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[sammy.se]

Thanks all for the great advice. I'll book it in for a service at the same time.

Out of curiosity, would a damaged lambda sensor give a fault code?



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[Crasher]

Yes, and it would bring on the Malfunction Indicator Light (MIL)