Maximum MPG out of a diesel

[Deleted member 89374]

I'm asking about older IDI diesels. I'd switch to 10W30 HDEO, synthetic ATF and synthetic lower viscosty gear oil.

Quaker State Euro 5W-40 - it's a dual gasoline/diesel oil, good fuel economy.

 

[Wizz]

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.

That is correct and great advice. I have very little experience with actually building diesel engines (only 'refreshed' them), but they do have a scientific sweet spot. Stoichiometry is involved in the calculations and the engineers gear accordingly, and staying in that RPM range makes a noticeable difference. In gasoline engines we would adjust the quench area.

Thinner oil fuel savings are not noticeable on an individual basis, it only makes an impactful difference on a global scale (many vehicles switching over).

 

[meadows]

My excursion got the best at 45 mph.

 

[Ray S]

Disabling the EGR often improves efficiency. But not always. Some engines have injection timing that is altered to accommodate the high EGR flow. One thing is clear, today's best "on road" modern diesel engines with cooled EGR systems and DPF are nearly all pushing 44% thermally efficient. That is exactly the number achieved before all this "tech" in the late 1990's.

Definitely true on the old Geo Metros - deleting EGR messes with the map and delays warm-up. My 94 gets 52mpg at 70 mph
https://geometroforum.com/the-94-metro-project-t23039.html

 

[OHChevy3.0]

Thinner oil fuel savings are not noticeable on an individual basis, it only makes an impactful difference on a global scale (many vehicles switching over).

I see no difference running 0W-20 or 5W-30 in my LM2. I've had both when running long distance trips (700+ miles one way at highway speeds). I prefer the higher shear of the heavier oil in the summer when towing so switch to the 5W-30 in the spring and back to the 0W-20 in the fall. YMMV

 

[dumkid]

If you can find it, take a look at the efficiency graph of your engine and it's BSFC. Maybe this can help you determine the proper speeds and loads.

Disabling the EGR often improves efficiency. But not always. Some engines have injection timing that is altered to accommodate the high EGR flow. One thing is clear, today's best "on road" modern diesel engines with cooled EGR systems and DPF are nearly all pushing 44% thermally efficient. That is exactly the number achieved before all this "tech" in the late 1990's.


Good turbocharging, proper injection timing, and unrestrictive intake and exhaust are all important factors in modern diesel engines.

dpf doesn't raise efficiency afaik, and scr is just magic sauce in the exhaust pipe for emissions. a dpf does increase backpressure which might get better economy. the main reason modern diesels get better efficiency is they run higher boost, the injectors spray finer mist, and the computer limits excess fuel. (if you floor an old mechanical diesel, you get all the fuel while if you floor a modern diesel you only get the fuel you need)



also short tripping a diesel (like only 10 km) wont let it warm up fully and you might have carbon buildup problems (more common on egr/dpf diesels)

 

[userfriendly]

Would a used LPG or CNG dual fuel system work, with Diesel as the pilot (start-up) fuel?

 

[Jetronic]

Would a used LPG or CNG dual fuel system work, with Diesel as the pilot (start-up) fuel?

it would, but no savings there. Not sure he can get it certified either.

 

[Bailes1992]

it would, but no savings there. Not sure he can get it certified either.

Volvo make a 'Methane Diesel' engine which in light-load situations uses gas as the main fuel and diesel as the pilot. Where extra torque is needed, the gas it replaced with diesel. Quite interesting.

 

[userfriendly]

Volvo make a 'Methane Diesel' engine which in light-load situations uses gas as the main fuel and diesel as the pilot. Where extra torque is needed, the gas it replaced with diesel. Quite interesting.

www.hhpsummit.com

 

[Jetronic]

Volvo make a 'Methane Diesel' engine which in light-load situations uses gas as the main fuel and diesel as the pilot. Where extra torque is needed, the gas it replaced with diesel. Quite interesting.

I worked asa mechanic at a bus company (I'm a driver now, for a different company) where they converted busses to run on LPG before my time. Spoke to the old engineeer who did it, apparently they could run on lpg from cold but smoked a lot until warmed up.

 

[Bailes1992]

I worked asa mechanic at a bus company (I'm a driver now, for a different company) where they converted busses to run on LPG before my time. Spoke to the old engineeer who did it, apparently they could run on lpg from cold but smoked a lot until warmed up.

I'm assuming these were petrol powered busses initially?

 

[Jetronic]

I'm assuming these were petrol powered busses initially?

No, diesel

 

[Chris142]

The best way to increase mpg out of a diesel is to drive down hill.

 

[The motor guy]

Does higher egts mean more fuel being burned? Towing a trailer I can have about 150 degree difference between 5th and 6th gear. 6th gear has a higher egt temp.

 

[Jetronic]

richer AFR means higher EGT yes. If you both double the air and the fuel, EGT won't rise much but pressures and power would double..

 

[userfriendly]

Does higher egts mean more fuel being burned? Towing a trailer I can have about 150 degree difference between 5th and 6th gear. 6th gear has a higher egt temp.

Sustained high EGTs can damage your turbo. Add more air before you add more fuel.
IMO there's little to be gained and a lot to lose running a light duty Diesel at high loads at low rpm.

 

[CDX825]

Does higher egts mean more fuel being burned?

Most of the time yes. Boost and RPMs will affect EGTs but generally speaking higher EGTs are from more fuel being burned.

 

[JHZR2]

If the injectors are clogged, rebuilding them will clean them up and flow more fuel. Mileage may drop but you will have more power.

On a diesel it’s less about being clogged, more about popping at the right pressure and having a good atomization pattern.

 

[JHZR2]

I'm doing some research and already have figured a workaround haha. And it will still look stock. All i have to do is plug the vacuum line that commands the EGR and keep the baffle in the intake from closing. That way it will only draw air from the airbox. I'll remove the EGR and clean it, my fear being that the excess crud will keep the EGR slighly open.

That depends. Some engines have a vacuum actuated wastegate and so that won’t work. You’ll need to retrofit a pressure actuated wastegate then.

https://www.peachparts.com/shopforu...tegate-actuator-swap-om602-962-revisited.html

I don’t know the exact situation for your engine….