back on the MPG thing

[LCAM-01XA]

So, I ran to Brooklyn (NY) his weekend, left home at 1am Saturday and was back around 11am on Sunday. Here are some MPG numbers for y'all:

- Ohio flatlands, fair weather - 20mpg.
- Pennsylvania hills, fair weather - 18mpg on first tank, then back up to 20mpg.
- New Jersey and New York, fair weather, including idling in front of the Brooklyn tunnel for an hour - 16 mpg.
- Pennsylvania hills, absolutely nasty weather (very heavy rain) - 15mpg
- Ohio flatlands, light rain - 18 mpg.

This was all running at 1950 rpms (58-61 mph depending on incline), cruise control all the way throttling on uphills and engine braking on downhills, except NY of course. All in all I'd say pretty decent results, even tho truck was empty one way and lightly loaded with a bit less than half a ton on the way back.

 

[8v-of-fury]

I was under the impression that diesels ran better when the air they were ingesting was moist.. but your numbers say im wrong.. Lol

Is this true, or did i dream it in one of those crazy dreams I have where everything is pink and covered in flowers?

Seriously though, don't they run better when its damp out?

 

[LCAM-01XA]

Well, mine don't, never did - I think it has to do with how water droplets don't burn and make power. My truck absolutely loves cold dry air, or at least cool dry air, really anything under 50F and dry and she pulls strong.

 

[Diesel JD]

I would have thought you'd do better with the slightly wet weather too. It might have to do with some other factor like increased wind resistance with the rain or not being able to be in overdrive and still not kill yourself. If moisture was bad, why would anyone do water injection?

 

[8v-of-fury]

If moisture was bad, why would anyone do water injection?

dang, you beat me to it. True! I'm pretty sure wet days increase diesels efficiency and performance, you have a rare breed of diesel i think lol

I think i read that the increased moisture in the air is just like the water injection where it is completely naturally cooling the engine by being injected along with the air.

on a side note, water injection how is it done? Is it a mist injected in the intake?

 

[Diesel JD]

Water injection, done very very carefully. If you have a turbo it must be downstream from the turbo. Its gotta be a very fine mist, if it ever dumps, it'll hydrolock the motor. Rob F350 has a good writeup on it somewhere. The benefits are keeping the EGTS and smoke emissions down so you can dump in more fuel.

 

[LCAM-01XA]

I would have thought you'd do better with the slightly wet weather too. It might have to do with some other factor like increased wind resistance with the rain or not being able to be in overdrive and still not kill yourself. If moisture was bad, why would anyone do water injection?

Rain was a huge factor while in PA, imagine if you're falling on the ground and there's a pissed-off hedgehog right where your face is about to plant - yeah, that's what I was seeing through the windshield, a big watery hedgehog!

Dunno about the water injection thing, maybe there's a limit as to how much water should be in any amount of air and when tis all wet and rainy the humidity is above that level?

 

[8v-of-fury]

dang, you beat me to it. True! I'm pretty sure wet days increase diesels efficiency and performance, you have a rare breed of diesel i think lol

I think i read that the increased moisture in the air is just like the water injection where it is completely naturally cooling the engine by being injected along with the air.

on a side note, water injection how is it done? Is it a mist injected in the intake?

So.. an n/a engine the mist would be injected in to the intake?

@ M.L.S.C that seems like it is.. a bit to wet of conditions eh? lol That would probably be equivalent of dumping water in the intake

 

[sootman73]

my truck runs way stronger when it wet and rainy. easily felt in acceleration. throws ya back into the seat much harder.

 

[8v-of-fury]

i've noticed it in my gasser VW as well

but in the 6.9 a wet day is its delight!

 

[david85]

My truck is usually happy in the fog or light mist. Even spray kicked up from vehicles in front of me can have a effect on how it runs. I can observe a good 50F drop in EGTs like that. In actual rain, its usually worse simply because when it rains in BC its never a light rain. Once it collects on the road its enough to increase rolling resistance and wind drag (often windy when it rains). The engine may very well be running better for me, but it also has to work harder.

 

[LCAM-01XA]

Same here Dave - engine itself may be working better, but tis also working harder (especially me having 4 wheels across the rear axle), so whatever performance gains I may experience get totally walked on by the drags... Never actually drove it through mist tho, it just never happened, I'll make sure I try to remember to watch its behavior when I get to do it tho.

 

[Agnem]

I think those who mentioned rolling resistance are on the right track. Usually when it is raining, there may be additional wind, your headlights and wipers are on, so there is a heavier electrical load, water is collecting on the vehicle adding to the weight, their may be higher humidity, which may actually reduce the amount of oxygen in the air. Cool dry air is going to be much denser then warm, heavy, wet air.

 

[LCAM-01XA]

Oh yeah, rolling drag was definitely an issue, especially on the Ohio Turnpike - as nice as the eastbound lanes are, the westbounds have pretty decent tracks caved in them, so they pool water nicely. Electrical load was there too, I was running my high beams and my four 100W auxiliaries, can't imagine that being any easy on the engine either.

 

[jeffgordon24]

may i ask what size tires your running on your rig cause my 94 f 250 4x4 with 4:10 and zf5 tranny runs at 2200 rpm at 60 and i got 245 75 16 tires