Date:         Fri, 1 Jan 1999 13:01:57 -0800
Reply-To:     YauMan Chan <YAUMAN@CCHEM.BERKELEY.EDU>
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         YauMan Chan <YAUMAN@CCHEM.BERKELEY.EDU>
Subject:      Re: warm up time - a contrarian's view! (longish)
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I would like to respectfully disagree with Ken's advice regarding the necessity of warming up the engine before moving the van. (I won't quote Ken here since my treatise is almost as long as his!)

I do not disagree with any of his analysis of engine warm-up thermodynamics or oil viscosity hydrodynamics.  Those concepts are all scientifically sound and correct.  However, I question the necessity of letting the van sit still while the engine is being warmed up *cold buns notwithstanding. The only differences between letting the van sit or driving it while warming up is the engine RPM and load on the engine. 

1. In the old days of either manual chokes or auto-chokes with mechanical springs, the air/fuel mixture control is very coarse and imprecise.  In those days, the advice to not move the vehicle while warming up was to prevent loading up the engine when the air/fuel mixture was not properly set and when the power output of the engine was lacking during the transition period between choke and non-choke operation.  During this warm-up period with wrong or fluctuating air/fuel mixture makes the vehicle basically undrivable.  Bad air/fuel mixture ration can cause great damage to the engine when run at high RPM.  This is no longer the case with today's computerized air/fuel mixture control and fuel injection engines.  The greatest advancement in this case are tiny, highly sensitive solid state temperature sensors (thermister) which allow the engine management computers to monitor the temperature accurately and adjust air/fuel mixture accordingly with high precision unattainable in the days of bi-metallic spring actuated butterfly valves!  This advancement in automotive electronics has made the car totally drivable while the engine is warming up.  As far as I know, no auto makers since the 1980's recommends warming up the car standing still in the driveway.  The recommendation is to drive "gently" while the engine is cold.  In fact, the recommendation is specifically to NOT warm up the engine at idle speed.  Warming up a modern engine should be done at normal operating RPM.

2. Lack of lubrication is the cause of wear, whether the engine is loaded or not. A load on the engine and running it at higher RPM than idle speed will warm it up faster.  If the proper "vanagon rated" oil filter is used (with the proper anti-backflow valve and high-pressure bypass valve) oil starvation experienced by the engine in the first 10-30sec after startup in a cold morning can be avoided. (So, alright, warm it up for 30 seconds!)

3. A case can be made for front engine cars that a moving car with cold air blowing into the engine compartment will delay the warm-up process.  (My Audi had a door behind the front grill I can close off for winter driving!) This is not the case with the rear engine Vanagon. (Does the air scoop in the D-pillar really do anything?)

4. Warming up for 15 minutes without moving the van is a waste of gas.  As long as the engine is running, go somewhere with it! Now we may debate the geo-social/eco-political relevance of this statement in another forum. But 15 minutes of burning gas per car going nowhere, multiplied by a few million is non-trivial waste.

Having said all that, I will concede that if your first trip in the morning is a quick 3-minute jaunt to the nearest Dunkin Donuts for breakfast, you should probably warm up the van or take a longer detour to get there!


Yau-Man Chan
87 GL