Maximum MPG out of a diesel

OM605

OM605

Joined
Jan 3, 2020
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Brittany
For obvious reasons, fuel economy is more important than ever. I am hypermiling as much as i can but have only owned gas cars for the past few years. Now i'm trying to squeeze every km i can out of each tank in this thing: https://bobistheoilguy.com/forums/threads/my-new-horrible-beater.361149/

What i've done so far is the basic stuff: new air filter, new 15W40, high tire pressure. How many of you have experienced increased fuel mileage out of switching to synthetic/lower viscosity fluids specificaly in your diesel cars or trucks? I'm asking about older IDI diesels. I'd switch to 10W30 HDEO, synthetic ATF and synthetic lower viscosty gear oil.

I'm also tempted to rebuild the injectors since i have a bit of white smoke on startup, maybe clean the pre chambers as well. Can you get extra mpg by rebuilding the injectors? To the diesel guys out there, you are welcomed to chime in. 😀
 
Gearshift indicators in modern diesel engine'd cars seem to get you to drive around 1400rpm-1600rpm.

However, I've always found I've gained an extra few MPG by letting the engine spin a little bit faster. I accelerate between 2500 to 3000rpm and then settle the car to a cruise around 2000rpm.
 
atikovi said:
You bought the car cheap so that's where your savings are. Don't worry about a few extra mpg's, it will drive you crazy. Spending $1000 or whatever it costs to have the injectors pulled and rebuilt will take 10 years of driving to break even on. By that time you will probably have an EV anyway.
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I think it would cost from 100 to 200€ to rebuild them myself.
 
How warm does the oil sump get? I am thinking thinner oil might help. Especially if it never heats up, due to short drives and light throttle.

Beyond that, weight reduction, high psi, and avoid driving. Get a folding bike and toss into the trunk, and pedal the last couple of miles.
 
supton said:
How warm does the oil sump get? I am thinking thinner oil might help. Especially if it never heats up, due to short drives and light throttle.

Beyond that, weight reduction, high psi, and avoid driving. Get a folding bike and toss into the trunk, and pedal the last couple of miles.
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Yes, being more organized and driving less comes a long way. I also carry nothing other than a few tools and a spare tire. This is the beater car (not to say that the other ones aren't but it's the worst haha) and is not the one i take for long drives, it sees a lot of 5 to 10 km trips, even less when i have to carry something heavy.
 
M119 said:
Yes, being more organized and driving less comes a long way. I also carry nothing other than a few tools and a spare tire. This is the beater car (not to say that the other ones aren't but it's the worst haha) and is not the one i take for long drives, it sees a lot of 5 to 10 km trips, even less when i have to carry something heavy.
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At 5-10 KM trips, in cold weather, I would be driving the petrol powered car-the Benz isn't going to be fully warmed up at 3.1-6.2 miles.
 
I've never owned a diesel but lower speeds will probably help more than anything. When I moved from NC-KY in 2010 I rented a 24' moving van that was diesel powered. It was loaded front to rear and nearly bottom to top so it had a good size load. I drove about 55 MPH on the trip for safety since I wasn't used to driving a vehicle that large or with that size load. For the trip I was able to get about 10 MPG which included driving across the Smoky Mountains on I-40. I can also vouch for lower speeds helping in gasoline engines, Lots of my driving is on secondary roads with high deer population so I usually only drive around 40-45 MPH and pretty much consistently exceed 50 MPG in my 2016 1.6L Nissan Versa with a CVT. My Versa is EPA rated for 31 city, 39 highway and 34 combined. I also do lots of coasting when I know I'm going to have to come to a stop instead of staying on the gas till the last second then jumping on the brakes and losing all the momentum from the gas I've already burned.
 
atikovi said:
If the injectors are clogged, rebuilding them will clean them up and flow more fuel. Mileage may drop but you will have more power.
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They tend to have a poor spray patern when worn, rather than being clogged. That's why there's a bit of white smoke on startup because of the big fuel dropplets not being properly burnt.
 
atikovi said:
If the injectors are clogged, rebuilding them will clean them up and flow more fuel. Mileage may drop but you will have more power.
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They could flow more, and better, but in the end, a light foot is a light foot on a diesel. At least the older ones.
 
bullwinkle said:
At 5-10 KM trips, in cold weather, I would be driving the petrol powered car-the Benz isn't going to be fully warmed up at 3.1-6.2 miles.
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Why? I would think the stone cold gasser might burn more fuel, thus cost more for that 5 miles drive. Not sure on the age of this diesel, but the gassers often ran rich initially to get the cat to warm up faster.
 
supton said:
Why? I would think the stone cold gasser might burn more fuel, thus cost more for that 5 miles drive. Not sure on the age of this diesel, but the gassers often ran rich initially to get the cat to warm up faster.
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The fuel mileage is appalling in my gasser for short trips, almost double the diesel.
 
Just keep up the maintenance, if the car is in tip top shape, then you should get the max mpg out of your car.
 
M119 said:
Does it help? I'd like to but i don't think it is legal unfortunately.
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Yep, tremendous gains in fuel savings.
Unfortunately it's not legal in all parts of the world, but you can count that an enthusiast will always find a workaround.
 
Bailes1992 said:
Gearshift indicators in modern diesel engine'd cars seem to get you to drive around 1400rpm-1600rpm.

However, I've always found I've gained an extra few MPG by letting the engine spin a little bit faster. I accelerate between 2500 to 3000rpm and then settle the car to a cruise around 2000rpm.
Click to expand...
Interesting, when tractors still had manuals (well they do, what I mean is when they were common in fleets), transportation cos. had campaigns to teach older drivers to shift at a lower RPM, because the "modern" 2010 engines didn't need to be revved up as high as the ones when they started driving. I seem to recall 1600 rpm v 1900 rpm translates to millions of dollars of savings
 
In my experience, you can optimize efficiency in a diesel if you keep it in a certain RPM range as much as possible. That range differs slightly from engine to engine, but for many diesels the sweet spot is 1,900-2,100 RPM.
 
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