[s-cars] Wet Engine

[qshipq at aol.com]

 Say what-hunh?? Light-up time on cats at idle in production cars is currently under 30 seconds (some under 15), and for the S car IME well under 2 minutes - it's federally mandated.? Cats most certainly do work at idle on an S car.? A cat will start operating at under 250C, optimum temp is usually 650-850c - when it needs to be, in a dynamic driving environment.? An idling engine has less pollutants than any driving engine, so cat efficiency at idle needs to be minimal, because a EFI engine at idle has pretty clean emissions, plus idle is the only state where A/F ratio is operating at 1lambda.? To the Oil 'wear' argument, I claim oil change interval and viscosity of oil makes a bigger difference than 'warm-up idle' wear.? To support this, a lot of research was done by Audi:? SAE 970922 Development of Modern Engine Lubrication Systems (FEV Motorentecknik and Audi AG)

Me, I wouldn't go past idle until it idles smooth.? If there is a rough running car, "warming" it up by driving it can damage the cats permanently with some sort of misfire or fueling problem.? I'd start with Ben Swann's Cklist myself - maybe even get vag-com on it and check measuring value blocks.? I've gotten a lot of S cars back after a 'engine spray' at the car wash, and the problem many times was solved by removing all sensors, cleaning them with compressed air, and using Stabilant 22.

I personally think all this greenhouse theory and engine/oil wear at idle is silly rubbish. ? To a wet engine that isn't running right as I read it in the post, a 'warm-up' drive is the last thing I'd consider.? 

My .02

Scott J
QSHIPQ Performance Tuning


 

-----Original Message-----
From: Cody Forbes <cody at 5000tq.com>
To: Brett Dikeman <brett.dikeman at gmail.com>
Cc: audigirl4ever at hotmail.com <audigirl4ever at hotmail.com>; s-car-list at audifans.com <s-car-list at audifans.com>
Sent: Mon, Sep 14, 2009 8:59 pm
Subject: Re: [s-cars] Wet Engine










I'll add to Bretts comments.

Work creates heat. An engine idling is barely working at all, maybe  
using 2% of it work capacity. An engine under load from driving gently  
during warmup uses a totally guestimated 40% of it's work capacity.  
More work, more heat. Until the thermostat opens you are heating a  
mass of metal and coolant with basically the same cooling capacity  
(airflow through the radiator doesn't matter until the thermostat  
opens) but by creating more heat by driving you heat that mass faster.

Besides increased wear from the bits not being at operating dimensions  
you have a lower oil pressure at idle than at... more than idle ;-).  
Also when an engine is cold it burns rich (adds excess fuel) because  
the fuel doesn't burn as well in a cold chamber as in a hot chamber  
(simplified, there are other reasons). This increases emissions of  
green house gasses. Making it even worse is the fact that the  
catalytic converter doesn't work cold so the extra greenhouse gasses  
just pass right on through. The ONLY way to warm up the cat is by  
increasing the exhaust gas temperature, which will NEVER happen at  
idle. Even sitting still in a traffic jam your cat will cool down  
below it's op temp.



-Cody (mobile)



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