Maintenance and FE
 

A few weeks ago the scenic went to the mechanic for a regular 15000km (9300 miles) maintenance. Since then, the consumption when coasting in neutral is lower than before.

• Before maintenance the consumption was at 1.4L/100 (168mpg) when coasting in neutral at 60km/h, ie 0.84L/h = 0.22GPH.
• Since maintenance it's at 1.2L/100 (196mpg), ie 0.72L/h = 0.19GPH.

As the consumption is shown with +/- 0.1L/100, this is at least a 8% saving when coasting in neutral...
(my cars aren't SG2 compatible and the scenic doesn't show the instantaneous consumption under 35km/h (22mph))

From car's manual, any *w40 oil is OK from 0w40 and up. The mechanic uses 10w40 by default and was very astonished that I was asking for 0/5w oil. He didn't had any 0w oil.

I find that improvement too big for a simple maintenance and I think the oil change from 10w40 to 5w40 and the air filter change aren't the only reason to such a big change. Not the lower temperature, nor the higher humidity are helping FE.

What is your experience ?

Denis.

Do you know what was done besides air filter and oil?

I read the invoice again and they :

• changed the oil & air filters
• changed the oil (5w40 ELF)
• verified all the liquid levels and added cooling and windshield liquid
• verified wipers, breaks and springs

Except filters and oil, I don't see anything that would explain the FE change while coasting in neutral.

Today I had dozens of occasions to look at these numbers : at each city entering I coasted from 90 to 50km/h (56 to 31mph). With a warmer temperature (8°C/46°F instead of 2°C/36°F) and a lower humidity (<60% instead of >90%) I have seen several times a 0.8L/100km while decelerating changed to 0.9L/100km at 60km/h, which would correspond to 0.54L/h (0.14GPH).

Denis.

Check you tires,
Perhaps as a courtesy the technician checked and lowered the pressure to the door sticker and did not realize you had them inflated for FE.
Tire pressure from 50 psi to 30 psi is going to make a difference you can feel.
Just a thought,
S.

The FE did improve at idle from 0.22GPH (Gallons Per Hour) to 0.19 (and even 0.14 with a warmer and dryer weather).

Tire pressure doesn't change the instantaneous consumption while the engine is idle when coasting in neutral.

I'm OK that placard will make coasting in neutral shorter than sidewall. Anyway right before my Xmas challenge [1] I verified the tires, they were at more than 3.0 bars (43 psi) and pumped them up to sidewall (3.5 bars = 51 psi).

I got the car at 60000km and I make a maintenance every 15000km, so this is the 5th for me. The calculated idle numbers were consistent until that last maintenance. I can't believe that such a simple change from 10w40 to 5w40 can improve the FE at idle for more than 10%.

Denis.

[1] more about it later, I'm working on the data. You can read comments in my last 2 tanks.

Quick question to all...

How many change their oil at 5,000 miles instead of the "old" 3,000 mile segments?

Heck, my Mazda6 dealer now says go 7,500 miles but I am hesitant of doing so. I am going to change it in a few hundred miles since I have gone 5,000 miles now but I am just wondering what everyone's interval is ... ?

Groar,
Are your findings with the car just started up or after its at operating temp? The lower weight oil should make a noticeable difference on start up because the it doesnt have to warm up as much to achieve its operating viscosity. I know an old van my parents used to have said in the manual to use different oil weights depending on winter or summer. At least thats the only reason that comes to mind, unless your air filter was really really really dirty.


basslover911,
Thats a bit of a loaded question. Its really the same kind of deal as whether to do aero or weight reduction mods.

If you do mostly in city driving, I would recommend changing the oil every 3-4k miles, if mostly highway you can get away with 5-7k. Highway miles are easiest on the engine since it keeps a fairly constant load and isnt being asked to work as hard.

Over the past few months my driving has been about 75% highway, I changed the oil at 5k and I could still see through it, it had barely begun to darken. Huge difference from the old oil changes with mostly city driving and a lead foot. When I would change the oil then after about 3k-3500 miles it would be DARK.

I've gone from 3K to 4K to 5K now, which puts me at about 3 oil changes a year. I never drive it less than 5 miles and it gets a fair amount of long trips in. I am in no way concerned that this is too long an interval. Most research I have seen on oil life backs me up. No need to throw away perfectly good oil to meet some arbitrary, outdated standard.

My older car (1997) is at 10000km (6200 miles) while my newer one (2001) is at 15000km (9300 miles).
In my older car the oil level begins to lower at 8000km while the newer one arrives at min oil level at 15000km, so I respect these milestones.

I know newer cars are at 20000km (12400 miles) and some have been up to 30000km (18600 miles) but then people were mixing "low maintenance" and "no maintenance"... so newer cars tells you the distance remaining before next maintenance.

Now all that I know is French diesel, but I have always been told that diesel need more maintenance than gasoline. This may not always be the case with newer diesels.

Denis.

When the car is at operating temp.
Is it possible a 10w oil isn't 100% synthetic ?
I heard the 5w can only be synthetic. The 5w used (8100 X Clean) is 100% synthetic : MOTUL

The air and diesel filter may also be a possibility, but it was the 6th maintenance and I never saw such a difference.

I plan to visit my mechanic when he is back from holidays to know more about it and see the difference between his 10w and 5w oils. He insisted on the fact the 5w is more expensive and it was 20% more expensive. It may be some magic with some additives in this oil, or some magic from new kind of filter, or...

Denis.

I have been directed to page 9 of this : http://www.iea.org/Textbase/work/200...e/calwell2.pdf
It show % saving against the 3 phases of driving cycle.

A little search gave me this link : http://www.ataevents.net.au/tmc/spea...sh-Castrol.ppt
Slides 13 to 15 say that the main parameter for lubricant fuel economy is engine load.
As my observations are at idle, this is when the load is the smallest.

Denis.

I'm thinking your improvement is from having slightly thinner synthetic oil put in and the new oil filter. I don't really know how much hp an oil pump uses but pushing oil through a clean filter has to use less.
Even if your new oil isn't synthetic odds are it is still slightly thinner at higher temps than the old 10w40.
I run shell rotella T 0W40(diesel oil) in my ATV, its the only rotella T that is full synthetic, it might be available by special order through your mechanic? It says on the jug that its made for extreme climates like Canada but I'm sure the Alps can get just as cold.
Ian

Before maintenance:

Bought a 152,000+ mile 3 cyl Geo Metro and drove it the 200 miles home. It got 46 mph vs EPA 49.

I took out 70 lbs, changed ONLY the plug wires, cap, and rotor. I aired up the tires to only 40 and put on homemade headlight covers. The FE is now 50-57!

Though the lighter wt helped, all of these trips involved carrying one way a set of Mustang rims (99 lbs), a set with tires (198), or even 2 full sets (396 lbs). With the 2 full sets acceleration was B A D ! The 1 full set would hurt the FE about 2 mpg.

I did not change the plus yet since it was only rough running at idle and smooth on the road.

When I do drive on open roads I go about 58-62 in 55 mph zones and 65-68 on the 70 mph zones....someday I should try an unloaded trip at only 55 or 50 to see how much better the FE can be...57.0 has been my best on three different trips. My car also gets better FE at the higher speeds compared to the 55 mph zones that involve going through a few small towns with slowing and stopping, even though I FAS. Pulse and glide makes worse FE in my car since it takes too much energy to get back up to speed.

Should have read PLUGS!

The air filter wont affect fuel economy like that, especially not a idle. I've put over 30k miles between air filter changes on my previous TDI without impact on fuel economy.

The oil change might have helped, but a >10% improvement in FE from switching oil is unheard of. Have you measured a difference in steady state driving under load?

My wife has the scenic since my Xmas challenge (we swap cars regularly) so I didn't drove it on my daily commute since. During my challenge I have seen 2.6L/100 instead of 2.8 at 80km/h and 2.2L/100 instead of 2.3 at 70km/h, but as it wasn't my daily commute I can't say if it's the same phenomenon or because I was on a little downhill my brain couldn't detect.

What is sure is that before the maintenance my wife was at 6.0L/100 and her last 220 km are at 5.3L/100 with colder temperatures. She has short commutes of 32 km round trip and does several smaller trips. I asked her if she changed something in her driving and she replied no.

I have to do the maintenance of the other car (4 years older : 97). The manual doesn't talk about 5W oils, only 10W and 15W. I'm wondering if I can use the same 5W40 oil. I'll ask the mechanic Friday.

Denis.

I saw the mechanic Yesterday and we talked about it. He didn't made anything else than what was mentioned : changed air & oil filters and oil. The 10W40 oil is a semi-synthetic one, while the 5W40 is fully synthetic.

He had no idea about what could have such an impact on fuel efficiency in idle. He was only afraid of the engine eating too much oil as they are using 10W on all engines except the newer with particles filters on which they use this 5W.

Yesterday the same mechanic did the maintenance of the megane, he changed air, diesel & oil filters and oil from 10W40 to 5W40. I'll see if this is confirmed with my wife's next tank in scenic and my next tank in megane I filled up today.

Denis.

Well I changed the oil at 5,000 miles and nobody said anything about the oil being to dark so I am guessing that everything was good.

I am also adding a PVC catch can, we will see how much blow by oil I get between oil changes.

I remember when i bought my car I changed the spark plugs, spark plug wires, distributor rotor, distributor cap, pcv valve, some hoses, air filter and tightened the throttle cable. The car bogged in 5th gear anything under 32mph. After I replaced all that I could put the car in 5th at 25mph with no problems. It's very hard to identify what the problem is so it's best just to do the maintenance on the car instead of just driving it till the problem arises.