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mpg vs rpms


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I have driven on freeway in Wyoming , Utah and Idaho all day and have been experimenting with speed, mpg, and rpms I have always tried to keep my rpms down to 1500 or below and my fuel mileage has not been that great. I believe my turbo does not kick in until over 1500 rpms. So today I tried running 1600 which puts my speed at 70.

Really pulls hills well at this combo and runs really smooth. And I am getting better mpg. Does this sound reasonable?

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Thanks MrSeas, I guess I will have to get one of those Scan Gauges. I just assumed the turbo worked at all rpms the same but I get a lot more boost when I go over 1500. I do not have a boost gauge.

I didn't mean to say you had to "invest" in a

ScanGauge D.

I was just pointing you at some info that was along the line of your observations that might be of interest to you.

I have the ScanGauge D and it is very useful.

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MrSeas, I have been wanting to get a scan gauge ever since I started reading about them. I do not have a boost or egr gauge. I think it would help me understand the engine boost better and tell me where is the best rpm to drive. I did not say earlier but I have the Volvo D12 engine. 465/1650. It is not governed on speed but the rpms I think are governed. I am getting about 7 1/2 mpg. I am just wondering if I have to drive 55 like in California should I hold 9th gear instead of going to 10th. I have the auto shift .

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I would be interested also like Rocky says. I have the same engine with a Freedomline. I run about 62 MPH and that is right around 1400 RPM. We get 8 MPG.

 

You will have a good time in CA. We were there last year and I'll tell you that if the sign says 55 MPH when towing that is what you do. We met someone that did not and was stopped in his class A. As far as we know the local LEO's never gave us a second look. Of course we try hard not to do anything obviously stupid to call attention to ourselves.

 

Glenn you will be glad to get the governor reset. It was just a computer setting on our Volvo. Very nice to have much more go when you need to go.

 

Brad

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Glenn, you need to get a list of all the things you need changed in the computer, so that you only pay one time. Weren't you having problems with ABS light being on after singling your truck? I thought that was a computer thing? Not sure about the FL though.

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Just as a disclaimer I cannot read EGT's on my ScanGaugeD (Cummins ISX). From what I have read this is an issue on most of the HDT's using a ScanGaugeD. So I added an EGT and Boost gauge.

 

I used this one.....

http://www.amazon.com/MaxTow-1500-Pyrometer-EGT-Gauge/dp/B0095YDMMU?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_search_detailpage

The EGT probe can be attached via a clamp to the outside of the exhaust manifold so no drilling required.

I was able to use an exsisting area in my dash for the placement of the gauge.

This is a "universal type" install and should work on any type/make of diesel engine.

 

I also used this for my boost gauge...

http://www.amazon.com/MaxTow-60-PSI-Boost-Gauge/dp/B0095ZDFH6?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_search_detailpage

It has an electrical "sensor" and you will need a place to "tap" into to get your boost. I was able to use an existing port on my intake manifold.

If you prefer you can also order this gauge with a "capillary" (hose) style sensor.

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This is Kevin Rutherford 101, they guy on the XM Truckers Channel(Sat-Sun 16:00 to 18:00 EST). I don't agree with alot of what he says, but his conversations about a "sweet spot" for every truck drive train/configuation has it's merits. He is the one who markets his version of a scan guage.

I have 2 gauges that came with my truck that have helped me for 1.7 million miles attain the best fuel mileage depending on the situation.

1. Turbo Boost gauge. Indispensable for this purpose. The higher the boost, the more fuel being consumed.

2, Real time fuel use gauge. Most Freighliner Century/Columbia/Argosy dashboards are equipped with a digital version expressed in mpg. Mine happens to be extremely accurate.

By using both, anyone here would be able to be a fuel economy champion in short order.

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I would be interested also like Rocky says. I have the same engine with a Freedomline. I run about 62 MPH and that is right around 1400 RPM. We get 8 MPG.

 

You will have a good time in CA. We were there last year and I'll tell you that if the sign says 55 MPH when towing that is what you do. We met someone that did not and was stopped in his class A. As far as we know the local LEO's never gave us a second look. Of course we try hard not to do anything obviously stupid to call attention to ourselves.

 

Glenn you will be glad to get the governor reset. It was just a computer setting on our Volvo. Very nice to have much more go when you need to go.

 

Brad

Brad,

I am at 70 and about 1600 rpms, 65 at about 1500 rpms 1400 is somewhere around 60-62. I do not get 8 mpgs at 62. I might need to replace my turbo boost sensor. I know some have changed the sensor but have not heard if it helped any.

Will the Scan Gauge D plug into the plug under the left side of the dash?

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"Will the Scan Gauge D plug into the plug under the left side of the dash?"

 

Yes that's where it plugs in!

 

Also be careful.... some years of Volvo motors do not play well with the ScanGaugeD!

 

Yes. I have a 2007 and it would cause the TCS system to fault.

 

The manufacturer said they have problems with 2006-2008 Volvos.

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Where is the real time MPG on our Freightliners? I found truck log and it shows fuel mileage since last reset. Not seen any real time mpg. Also what is 7mp on my display?

Glenn, do you have a bar of lights across the top of the readout that moves to the left under acceleration and to the right when coasting? That is the real time mpg. Dead center would be the 7mpg showing on the readout. More bar to the right means better that 7mpg and more bar to the left is less than 7mpg. You can change that number. Ours showed 10mpg when we got it and I changed it using the onboard menu to a more realistic 9 mpg.

 

Dave

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On the Freightliner "fleet" instrument panel there is no rectangular readout containing the real time mpg readout.

The panel in question is right at the top, measures about 1 1/2" by 10" and contains the odometer, real time mpg gauge and numerous(18 at least) square indicator lights(high beam, abs light, check engine, parking brake on, several others depending on options, like mine has an indicator that the kick out steps are not deployed)

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Glenn, do you have a bar of lights across the top of the readout that moves to the left under acceleration and to the right when coasting? That is the real time mpg. Dead center would be the 7mpg showing on the readout. More bar to the right means better that 7mpg and more bar to the left is less than 7mpg. You can change that number. Ours showed 10mpg when we got it and I changed it using the onboard menu to a more realistic 9 mpg.

 

Dave

 

 

I wondered what that display was for. Thanks!

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The boost sensor not only goes to a gauge telling you what's happening, if you have one, but it also is one of variables that tells the ECM how much fuel to get to the injectors, and in turn tells them what to do. That is why you lost power when the sensor went bad. The ECM was making decisions on bad information. No telling what it did to fuel economy in the meantime.

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I have to agree with Jeff's statement. LGT F350 dually, I drove by those gauges, not the factory, the ones I installed. 450,000 miles. 22 mpg in the summer and 21 mpg in the winter. I tried to keep the truck just out of boost and the EGT, pre turbo, about 400. 2thoughts on the winter, winter fuel and always had the lights on to and from work. Of course, summer was A/C and summer fuel. I could not tell a mileage difference A/C or not. Ford research said windows up, ac on was more efficient than windows down.

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Just as a disclaimer I cannot read EGT's on my ScanGaugeD (Cummins ISX). From what I have read this is an issue on most of the HDT's using a ScanGaugeD. So I added an EGT and Boost gauge.

 

FWIW the EGT on the ISX is "calculated". There is not sensor/probe. Maybe that's why the ScanGuage won't "read" it. Not sure about other Cummins engines.

 

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