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Old 05-10-2017, 06:08 PM   #11 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
I ran an electric cooling pump on my 5L Camaro ,suburban with a 454 and my 6.5L diesel.
I know pretty much all there is to know when it comes to electric cooling pump conversations.

As far as I could tell the electric pump gave no measurable fuel economy important. All it does is use more power and make an alternator delete more difficult.
The main benifit they give is being able to circulate coolant with the engine off.
Well, there's no question a water pump burns horsepower. I'm not sure how much, but even if it is only 2 or 3hp, it's easy to calculate exactly how much gas 2hp burns per hour and convert that to MPG at a given speed. Without an extensive dyno test, it's pretty hard to accurately see a 1-2mpg difference, there are just too many variables. If you don't delete the alternator or turn it off, then you are just moving the load from the water pump to the alternator.

But yes, I do want to use it to also preheat the engine, and cool the engine while it's off if it ever overheats. (Cherokees are notorious for overheating issues) I'd probably set it on a timer to continue running a minute or two after engine shut down, kind of like a turbo timer. This would prevent the heat soak that happens immediately after shut down.

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Old 05-10-2017, 06:09 PM   #12 (permalink)
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OP, check to see if your Jeep can be flat towed. If so, the auto trans will be fine doing EOC. If not, you do run the risk of messing it up.

FWIW, I did EOC in my non-flat towable Ford Escort and never had a problem. Granted, I did it sparingly and used neutral coasting and engine off at stops to increase my mpgs.
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Old 05-10-2017, 07:54 PM   #13 (permalink)
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If you want to talk about something that will actually increase fuel economy a noticeable amount then you need lean burn. When I went lean burn on my 454 I saw between a 10% and 20% increase in fuel economy.
Lean burn works.

The water pump uses hardly any brake horsepower at normal cruise speed.
The coolant pump doesn't use 2 or 3 horsepower it uses more like 1/6th to 1/2 horsepower.
The power the coolant pump uses is actually needed while the engine is running.
They only time the coolant pump uses 2 or 3 horsepower is at 5,000+rpm when pump flow is stalled and the impeller is cavitating like crazy.

Something you don't need running the entire time while rolling down the highway is the power steering pump.
It uses up to 1hp even during normal cruise speeds.

Removing a 1hp load will reduce fuel consumption by about 1 gallon over 12 hours of driving. To quantify to to MPG if you had a vehicle that gets 20MPG at 60mph. You would be burning 18 pounds of fuel per hour or getting 3.33 miles per pound of fuel. Saving 1 horsepower would reduce that to 17.5lb/hr or 3.43 miles per pound. Multiply your miles per pound to your chosen volume, a gallon of gas weighs 6lb.
Before saving one hp you got 3.33 miles per pound, times 6 pounds, for 19.98mpg.
After saving 1hp you got 3.43 miles per pound, 6 pounds per gallon for a total of
20.58MPG.
So removing the power steering load you could notice at the pump.
Removing the 1/2 coolant pump load completely at most you would see a 0.25mpg increase if you started at 20mpg. If the coolant pump load were close to 1/6hp which i belive it is, then it would increase fuel economy by close to 0.1MPG.

This is why removing the belt driven coolant pump isn't even noticed and why I don't recommend an electric swap for improving fuel economy.
Unless it's part of an engine off coolant circulating warm up mod.
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Old 05-10-2017, 08:50 PM   #14 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
Lean burn works.
Not on an OBDII controlled engine that was not designed to run that way.

I think you're missing the point about the water pump. The intention is to get rid of the belt entirely. Not only does this make the vehicle more reliable, but it gets rid of a lot of random losses from bearings, random idler pulleys, etc. Even the A/C, when the clutch is turned off, still wastes a little bit of power. Removing the belt entirely and everything that is powered by it will most certainly make a noticeable difference at the pump.

Also, having complete on/off control of the water pump helps greatly with warm up and cool down, and works great in combination with electric fans.

The change from V belts to serpentine belts caused an increase in fuel economy, removing the belts entirely gets even more. There is more than one vehicle these days coming with an electric water pump from the factory.
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Old 05-10-2017, 08:58 PM   #15 (permalink)
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For what it's worth, my car has a serpentine belt and all of its accessories are still attached, and I'm able to get in excess of 100mpg just driving in a straight line at constant speed, no tricks. I've thought about an electric water pump but as-is it's very reliable.
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Old 05-10-2017, 09:24 PM   #16 (permalink)
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For what it's worth, my car has a serpentine belt and all of its accessories are still attached, and I'm able to get in excess of 100mpg just driving in a straight line at constant speed, no tricks. I've thought about an electric water pump but as-is it's very reliable.
Yeah, but yours was designed for efficiency from the factory. Jeeps, not so much. I'm not saying serpentine belts are unreliable, just that my entire system is getting old and it's going to be more reliable with new electrically driven things.

Also, I don't do a lot of highway driving. I think the improvements would be better with constantly varying speeds. (and more opportunity for regenerative braking)
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Old 05-10-2017, 09:59 PM   #17 (permalink)
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As the others have pointed out, EOC is like towing...without the engine running, there is no pumping of the ATF to lubricate and cool the transmission. Most owns manuals say not to tow for more than X miles at no more than Y mph. You'd have to check yours to see what it says.

Chances are, you'll be fine for brief periods, but is it worth the risk to save a few pennies in gas each time?
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Old 05-10-2017, 10:25 PM   #18 (permalink)
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His Jeep is probably fine with flat towing, but not because the transmission can necessarily take it, but because you can just put the transfer case in neutral and be good. So a yes for flat towing isn't a definite green light for EOCing.
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Old 05-11-2017, 03:45 AM   #19 (permalink)
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Well, I guess you're right, according to the manual the transfer case should be put into neutral for flat towing of a 4WD. For some reason it doesn't say anything about a 2WD with the same transmission. I also see with a cursory google search they sell both driveshaft disconnect kits and electric transmission pumps to solve this problem for RV users. Most of what I can find in google says not to tow with the transmission in neutral for "more than a few miles", but I can't coast more than that anyway.

I'll have to do a little more research on that part. I guess I could just put the transfer case in neutral instead of the transmission. I would really love the equivalent of a clutch pedal that would put it in neutral and let me coast, though the driveshaft disconnects aren't very cheap. Unfortunately I can't drive a manual transmission very well due to some problems I have with my legs, it makes it hard to use a normal clutch.

To be honest, I don't have a chance to coast in neutral very often, just a short hill by my house. Probably not worth the trouble. Engine off during stop/idle would probably save more fuel with the traffic around here...

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Old 05-11-2017, 10:20 AM   #20 (permalink)
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Putting lean burn an an OBDII vehicle would be a lot easier and give more improvement than trying to create some kind of electro mechanical regeneration brake system from the ground up.

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