Should I let my diesel warm up before driving?

[jtanguay]

yeah that is wierd, our detroit always fires right up but it is a sorry excuse for a diesel!  no power

well too much advance = very low power...

[AudiVWguy]

Hi,
I seen Andrew's post about it being significantly worse to let the engine idle to normal operating temp. Could this be explained a bit more. For some reason I thought Idling for awhile (minutes) was better. I guess I was thinking it was less stressful to bring the components up to temp slower the better.
Thanks,
-JB

[jimfoo]

With 2/3's of my rad covered and a fast idle(hand throttle), my engine is up to at least 160 after 10 min of idling. I hate driving with the windshield freezing up on the inside, and have a poor defrost, so it idles every morning.

[jtanguay]

With 2/3's of my rad covered and a fast idle(hand throttle), my engine is up to at least 160 after 10 min of idling. I hate driving with the windshield freezing up on the inside, and have a poor defrost, so it idles every morning.

jimfoo how's the mTDI treating you?  good cold starts?

[dieselweasel]

You should wait for the oil light to go out before revving the engine and you should drive gently until it is up to normal operating temperature.  It is significantly worse for the engine to idle it's way to normal operating temp than it is for it to be placed under gentle load to get there.  BEST for any engine, gas or diesel, even in mild climates, is to install a block heater and use it pre-heat the engine year round to eliminate all cold starts.

Andrew

Thank you!  I HATE idling, especially when cold, for the reasons you mentioned in your posts.  Combustion is cold and sooty when cold, allowing deposits to form in the ring lands and on the valves.  Plus its a waste of fuel, a valuable resource. The guys I work with who are all mechanics go out and start their vehicles when its cold and let them idle for 10, 20 minutes.  Me, I start it, let it idle for 30 seconds-1 min, then drive off gently until it starts to warm up.  

What really drives me nuts is truck drivers are always complaining about poor fuel economy, yet many of them let their engines idle for long periods unnecessarily.

[blackdogvan]

Interesting discussion.

I don't see any comments on a cold engines oil pressure? I get a bit worried when I first set out about the oil pressure getting in the plus 100psi range & the effect on the seals in my turbo & elsewhere...

[1.6Lmarine]

Top of the piston is .0001 - .0002 smaller than at the skirt (measured across at the lowest full-sized point).  When the engine operates at a normal temp (160 - 180 F), the top of the piston enlarges (the hottest point) so that piston sides are parallel all the way down.  This gives the correct support for your rings.  Without being expanded the bore wears elliptically, oiled or not.  

I farm. A diesel's made to be worked.  It's not a machine to drive to the corner store and back.  That's disrespectful.  Had a Rabbit.  1 million miles before the engine tanked.  Drove it hard.

[Rabbit TD]

I also agree that these diesels use very little fuel at idle whch should translate to a slow warm-up.  But on the other hand, if they use less fuel at idle then why will the temps climb in the summer in stop and go traffic and the engine fan come on.  You would think just the idling alone would bring it down but it doesn't work that way and this engine uses a 180 thermostat and never runs over 1/3 of the scale on the guage no matter how fast you go in the Summer.  Block and head were cooked as well as the radiator and the rest of the cooling system works perfect as well and operates perfectly normal as far as I'm concerned.  But since we started talking about less fuel at idle and all it's got me thinking now which sometimes is not the best thing for me to do :lol:

[dieselweasel]

I also agree that these diesels use very little fuel at idle whch should translate to a slow warm-up.  But on the other hand, if they use less fuel at idle then why will the temps climb in the summer in stop and go traffic and the engine fan come on.  You would think just the idling alone would bring it down but it doesn't work that way and this engine uses a 180 thermostat and never runs over 1/3 of the scale on the guage no matter how fast you go in the Summer.  Block and head were cooked as well as the radiator and the rest of the cooling system works perfect as well and operates perfectly normal as far as I'm concerned.  But since we started talking about less fuel at idle and all it's got me thinking now which sometimes is not the best thing for me to do :lol:

I don't think that a diesel engine's lower fuel consumption has as much to do with not warming up as quickly as does its enormous appetite for air.  A diesel goes through significantly more air than a gas engine due to a wide open intake system.  When it's cold outside, the air coming into the engine is cold, which in turn cools the engine or prevents it from warming up as fast.  A gasoline engine on the other hand has only a small opening in the intake at idle which limits the incoming quantity of cold air.

The engine heats up more at idle in the summer because the ambient air is hot.  It will run hotter at idle than driving on say a flat road because there is no air flow across the radiator or engine.  Another factor in seasonal engine temperature is the climate control of the cabin.  Having the heater on takes heat away from the engine whereas having A/C on will place more strain on a cooling system.  

Also as a point of interest, with all else being equal, for every 1 degree F increase in intake temp, the EGT will increase approx. 3 degrees.