Diesels are very efficent at idle?

[GasSavers_Brock]

It takes FOREVER to warm up. Last winter when it was -10F or -23C with the front completely blocked driving on highway the engine temp never got above 150F and when I would slow down coming in to a town it would drop in to the 125F range. If you let it idle it will cool down, I never let it idle to long so I don't know how cold it might get. We have heated seat in the front and an electric blanket for the kids in the back.

I typically run a 120vac coolant heater when I am at home before I leave and when I leave it might be 190F and will drop to 160F by the time I am at work.

[Lug_Nut]

Diesels can have no throttle plate to reduce the airflow through the engine. Reducing the air volume (generating a manifold vacuum) will lower the amount of air in the cylinder to a point where compressing that reduced volume of air doesn't produce enough compression heat to ignite the fuel. At very low fuel use (idling for example) there is little fuel burned but a full volume of air moving that heat out the exhaust. As a result the engine coolant water jacket may not heat up. The engine is effectively internally air cooled.
It's not that the combustion is all that much more efficient, it's that the excess air takes too much heat away too quickly.

[Spule 4]

I had to flush out a few Mercedes diesels in my time.

We would take a papercup with diesel detergent (I think Sensydine made it, this was over a decade ago) and put the suction and return lines into it. The 5 pot Benz motors could idle off that cup for long periods of time.

[Ted Hart]

Originally Posted by JanGeo

A 10 mile trip in my xB with a 44mpg fuel use drops to 40mpg when it takes a few minutes to park in my usual spot. Really makes me think about where and how I park. Pulling out with a cold engine is more of a fuel burner so I always try to park so that I can just pull out instead of backing out and manuvering with a cold fast idling engine.

Kudos for your thinking on programmed parking!
For years, I have been parking...such that the car is ready to go downhill (a long slope) when initially started. This means I have to walk some distance, but I'm primarily concerned with engine wear and door dings! MPG is a secondary benefit! Twice a day times the number of days per work week ( 5 ) times 50 weeks per year...it adds up! 50 X 5 X 2 = 500! That's big!

[Ted Hart]

Originally Posted by rh77

Also, to answer a previous question -- diesels last longer because they're built to withstand the very high compression ratios of the combustion (thicker blocks and sleeves within the cylinder).

RH77

Correct! Plus (and it's a big plus!), diesel fuel is a lubricant. Oil is slicker than a solvent (gasoline). This makes a tremendous difference in wear rates!

[Ted Hart]

Originally Posted by philmcneal

on the plus side diesel is cheaper than gasoline at the moment!

The end of May,'06 ain't the middle of December,'06! Sometime in November...the price of diesel at the local rip-off convenient store PASSED premium gasoline in price! I can easily remember when diesel was less than kerosene...kerosene being exactly 1/2 the price of gas (same station)!Oil is more expensive than gasoline? ...to refine? On what planet? It looks like the greed factor is becoming more blatant! After all, look at all the power in the tiger's pocket.Grrr...(My growl...not the "fat cat").

[omgwtfbyobbq]

It could also be a convergence of factors, like...
-Holiday season, lots of time sensitive LTL freight
-Military action, plenty of demand there
-USLD requirements for the entire country
I'm betting that diesel will start to drop after new years.

[Sludgy]

The Scangage say that my Powerstroke diesel gulps down as much as 1.2 gph in winter cold. It decreases to about .4 gph in neutral when warm. The truck drops from about 17 mpg around town to 15 or so in winter.

Part of the high FC at low temp is due to oil viscosity, but Ford also installed a butterfly valve in the exhaust to make the engine work harder and warm up quicker. Another of Ford's freakin' "better ideas"? I think not.

Another low temp FC problem is the Powerstroke's belt driven fan. It has a fan clutch, but the fan still pulls cold air across the radiator and engine when the truck is warming up. Ford should have installed an electric fan. It would have helped both cold and hot FE. Morons.

[Lug_Nut]

Originally Posted by theclencher

... it seems to me that throttling back that excess air would be a sensible way to prevent overcooling... no?

You should have included this line from my post. It renders the discussion moot.:

Reducing the air volume (generating a manifold vacuum) will lower the amount of air in the cylinder to a point where compressing that reduced volume of air doesn't produce enough compression heat to ignite the fuel.

re: an earlier post about locomotives idling all night,
Massachusetts has a law prohibiting diesel idling for more than 5 minutes. The commuter rail engines used to each be left idling all night until the threat of fines made the rail authority come up with a solution. Now only one diesel electric engine is left running. The electric power from that one is connected to heaters in the others in the depot to keep them warm. The one running is not considered to be 'idling' as it is providing work.

[70 mpg jetta]

nox values go way up