Does air in fuel lines affect economy?

[Rich_91]

Lately, I had noticed that my 1.6L TD has been a bit more sluggish on startups. Wierd, since the outside temps have been getting better. It starts, but misfires for the first 20-30seconds, even with the cold start pulled. Fuel milage is going down.

I had a friend start it, while I watched the fuel lines, and there were TONS of air bubbles. After 30 seconds or so, the majority of them were gone, and the car runs good. Power seems ok, but economy is down. There is still bubbles, a few every 10 seconds or so.

I noticed that the top of my fuel filter appears wet. So, I will probably change that, and I should get rid of my water seperator too, since the lines are looking pretty rough. Should probably change a big chunk of my fuel lines.

I guess my question is this. Does air in the lines actually affect fuel economy? Or am I barking up the wrong tree? The car seems fine, except for the short stumbling on startup, and the poor milage.

Injectors are only 6 months old, bosch rebuilds.
New air filter
rebuilt turbo, boosting to 16lbs

I can live with the startup issues, but the milage is not good. 650kms on a tank is poor, in my opinion.

[Grunge]

bump for some input. my car has the same 20-30sec rough start. was also thinking about deleting the separator. mines a 1.9td in a 86 golf, but im getting about 700-800kms per tank

[ORCoaster]

With the kind of kilometers you state I would say you are good but could be a bit better.  I am not sure air affects mileage as much as it affects idle.  Unless there is foam coming out the return line.  Any air getting into the pump is compressed to how many bars?  150?  And then it is sent down the steel line to the injectors where the next bump of the pump moves the whole hydrological stream closer to the injector. 

Check for air at the outlet banjo as it returns to the tank on startup and high idle.  Small leaks seem to show at idle mores so than at high RPMs.

[damac]

You would think it was designed for fuel so all the air and disruption in how smooth the engine is would hurt at the end of the day?

What I find funny about my first vw experience with my jetta is with our constant mixed commute of 120+ miles/day that car pretty much gets 43mpg.  It goes up if sticking to the speed limit cruising in 5th on flat ground.

It got this when I first brought the car home.  Leaking oil and diesel all over the place, steady drips.  Shot suspension and generally abused car.  Still the same with all new suspension and alignment, balanced tires, fresh pump and pop tested injectors, etc.   Engine has had blowby since I brought it home and plan to rebuild the engine in the next few months.

I was hoping to get that 50mpg number all day long but I think thats pretty unrealistic with our commute I guess.  This has been with an acn tranny and stock turbo/fuel settings/tires.

[Doug]

It seems that every winter fuel mileage drops. This despite using a heat shield across the front of the vehicle as well as a block heater. I am sure that the fuel is exceptionally low quality probably cut with gasoline as there seems to be a glut of that right now looking at the prices at the pump. While diesels don't like cold weather I never remember such dramtic drops in fuel mileage before. It might have been down 10-15% in the past but recently it has been close to 25-30%. That tells me that fuel is the culprit.

[ORCoaster]

I didn't think there was a summer versus a winter diesel like they do for gasoline cars.  They aren't adding or taking away anything in it that I know.  It may be a reflection of how sensitive the diesel engine is to proper heat for combustion.  The extra loss in the winter may make that 10-20% difference.  Tire pressure is critical to mileage and if you are running snow tires width and studs can come into play.  I watch the pressure weekly in my tires, more because I have a couple slow leaks and I don't want to go two weeks with air loss.

Proper thermostat operation and balance for the type of driving you do is important for heat retention as well so you might consider these source areas and see if there is a change between now and summer operation for your car.

[vanbcguy]

I didn't think there was a summer versus a winter diesel like they do for gasoline cars.  They aren't adding or taking away anything in it that I know.  It may be a reflection of how sensitive the diesel engine is to proper heat for combustion.  The extra loss in the winter may make that 10-20% difference.  Tire pressure is critical to mileage and if you are running snow tires width and studs can come into play.  I watch the pressure weekly in my tires, more because I have a couple slow leaks and I don't want to go two weeks with air loss.

Proper thermostat operation and balance for the type of driving you do is important for heat retention as well so you might consider these source areas and see if there is a change between now and summer operation for your car.

There very most definitely is a different formulation for winter diesel versus summer diesel!

[R.O.R-2.0]

I didn't think there was a summer versus a winter diesel like they do for gasoline cars.  They aren't adding or taking away anything in it that I know.  It may be a reflection of how sensitive the diesel engine is to proper heat for combustion.  The extra loss in the winter may make that 10-20% difference.  Tire pressure is critical to mileage and if you are running snow tires width and studs can come into play.  I watch the pressure weekly in my tires, more because I have a couple slow leaks and I don't want to go two weeks with air loss.

Proper thermostat operation and balance for the type of driving you do is important for heat retention as well so you might consider these source areas and see if there is a change between now and summer operation for your car.

i was running a 180* thermostat as a universal summer/winter t-stat..

WAS...

now im running a 87*c (basically 190*f) thermostat, and my temp gauge basically stays put now. it used to fluctuate bad, going up hills it would rise, and coming back down the car would cool almost all the way back down to COLD. now the car doesnt even heat up when im POWERING DOWN going up hills.. car also has a little more pep once warm. turbo even comes on sooner with the hotter t-stat. mileage seemed to improve also.

im going to switch to a 160*f for the summer months tho.. give the car a little more head room to heat up if it needs to..

[ORCoaster]

Went to look for differences in summer/winter fuel.  Some say they thin it to decrease gelling, others say not.  I did find a 2007 study of additives for diesel and slap it in here as many of us have discussed this in the past and I remembered reading it back when.  Some may find it interesting.  Appears some of the over the counter additives score the cylinders more than others.  And to those burning WVO, slick.  

http://api.viglink.com/api/click?format=go&key=d1aa4f3f5a14e78235714f17d6ab0a00&loc=http%3A%2F%2Fwww.powerstroke.org%2Fforum%2Fbio-diesel-alternative-fuels-supplements%2F187552-difference-between-winter-summer-fuel-2.html&v=1&libid=1327426270105&out=http%3A%2F%2Frivrdog.typepad.com%2Ffiles%2Fcopy-of-diesel-fuel-additive-version-3.pdf&ref=http%3A%2F%2Fwww.powerstroke.org%2Fforum%2Fbio-diesel-alternative-fuels-supplements%2F187552-difference-between-winter-summer-fuel.html&title=difference%20between%20winter%20and%20summer%20fuel%20-%20Page%202%20-%20Ford%20Powerstroke%20Diesel%20Forum&txt=DIESEL%20FUEL%20LUBRICITY%20ADDITIVES%20STUDY%20RESULTS&jsonp=vglnk_jsonp_13274267042312

And this is what I wanted: 

http://api.viglink.com/api/click?format=go&key=d1aa4f3f5a14e78235714f17d6ab0a00&loc=http%3A%2F%2Fwww.powerstroke.org%2Fforum%2Fbio-diesel-alternative-fuels-supplements%2F187552-difference-between-winter-summer-fuel.html&v=1&libid=1327427117004&out=http%3A%2F%2Fdodgeram.org%2Ftech%2Fdsl%2FFAQ%2Fdiesel_fuel.htm&ref=http%3A%2F%2Fwww.google.com%2Fsearch%3Fq%3Dis%2Bthere%2Ba%2Bdifference%2Bbetween%2Bsummer%2Band%2Bwinter%2Bdiesel%2Bfuel%253F%26rls%3Dcom.microsoft%3A*%26ie%3DUTF-8%26oe%3DUTF-8%26startIndex%3D%26startPage%3D1&title=difference%20between%20winter%20and%20summer%20fuel%20-%20Ford%20Powerstroke%20Diesel%20Forum&txt=Diesel%20Fuel%20Characteristics%20and%20use&jsonp=vglnk_jsonp_13274271564203

Some real information on diesel fuels.

Should tiny URL these.

[bajacalal]

Should tiny URL these.

Or at least post the original URLs if you have them without all the VIGLINK crap.

Viglink is marketing. It is a service where if you have a webpage and you set up Viglink, you get paid when people click links that you provide, i.e. for products that you recommend on your website by linking participating manufacturers/retailers.

[ORCoaster]

I just copied the short cuts and pasted them and this is the first time I have seen this Viglink stuff.