What's better for fuel mileage..... cool fuel? or hot fuel?

[JAG1]

I don't know the answer to this one. I am hoping that all the fuel coolers sold do give better mileage as they claim.I know the vp can get too hot under loads, heavy towing and so on, esp. on hot days in which cooler fuel helps in that case.Anyhow, ever notice how hot the fuel filter housing gets from being mounted on the intake manifold? Put your hand on it after a run. It's supposed to be getting too hot anyways, acting like a fuel heater most all the time.First off I need to give credit for this information from another forum when this discussion was going on. Someone got the bright idea to make a plastic piece that isolates the fuel cannister from the engine heat. I did this with a piece of phenolic resin, about a one inch offset so it no longer sits on the manifold.Hopefully someone else can find this helpful however much this little mod does actually help...... I really don't know:shrug:. But it made me feel better anyhow with accomplishing one more step toward a cooler running vp.

[Mopar1973Man]

There is a balance to fuel temperature. You want it warm enough to make it thin anf easy pumping but also cool enough to take away heat from the electronics. The typical fuel temperatures I've been hearing is right around 120*F. I know that with the cold temps I get out here in Idaho the fuel thickens up and it hard to pump. Why I kept my stock fuel heater and filter. This way I can pull the heat from the manifold and heat the fuel up to get it thinned out again. Like my last trip to Ontario, OR I left New Meadows, ID at 5*F above and came home in 15*F above for evening temp.

[ISX]

There is a balance to fuel temperature. You want it warm enough to make it thin anf easy pumping but also cool enough to take away heat from the electronics. The typical fuel temperatures I've been hearing is right around 120*F. I know that with the cold temps I get out here in Idaho the fuel thickens up and it hard to pump. Why I kept my stock fuel heater and filter. This way I can pull the heat from the manifold and heat the fuel up to get it thinned out again. Like my last trip to Ontario, OR I left New Meadows, ID at 5*F above and came home in 15*F above for evening temp.

I have never read a thing about it being hard to pump if it's cold unless it is gelled. I have never experienced a thing with cold temps either. You never use your block heater and it starts right up down to whatever coldness, even with the 2 stroke oil which is the only thing I see getting harder to pump. In other words, I think temperature is insignificant unless it is gelled. I see nothing saying cold fuel is hard to pump. I know it is a law of physics or something but the fuel is too thin from the start. I have ran straight 2 stroke in my truck as a test and it had no problem with it and you know its a LOT thicker than diesel is ever going to get. I even have a jar of diesel outside and shook it at 10F and it was still the consistency of water. Fuel temperature itself will retard timing. Cold fuel is going to take longer to get hot enough to combust. However, I don't think that is a factor. The fuel is pressurized so fast and to such a high pressure that it gets very hot no matter what. I am not sure how hot but I would like to find out. The other factor is that the injection pump itself puts a lot of heat into the fuel. Moreso all the pumps other than the P7100 because they are all cooled by the fuel so the fuel absorbs a lot of heat. The P7100 just runs it in and injects, doesn't use the fuel for anything else. The VE pump trucks (1st gen cummins) are capable of the same or better mileage as a P7100 and they use the fuel to cool so that rules fuel temp out. I think whatever change in temperature it gets to becomes insignificant when it is pressurized to several thousand psi in an instant.

[JAG1]

It might be beneficial, in other words, to go ahead and isolate the filter canister off the intake manifold even if just for the sake of the vp electronics temperatures.Who really knows except the guys doing the test with remote temperature sensors. They are the ones saying the vp does occasionally get too hot going above factory specs. It's an easy mod anyhow and don't think anyone would want to actually add anymore heat to the vp if they did any heavy towing.

[ISX]

The problem is when you start it. I had JOHNFAK's truck for a week and his edge juice monitored fuel temps inside the VP. It was around 100F or so while driving it but when you turned the engine off and went to do something and came back 20 minutes later, it was already over 150F. That means when you start it again, that pump is very hot and the fuel takes a while to get it back down. It is the heat soak of the engine into the VP while there is no fuel moving that is the problem. Some people have tried peltiers I think on the VP but they are still fighting a losing battle. I still don't fully understand the heat issue vs. the lube issue. Mike is running 2 stroke and his pump has lasted for over 100k, yet then there is this solder issue as well. So there are 2 things against the VP as far as I can tell. I think they might have fixed the solder issue or something and now it is just a lube issue. I really don't know. I have never seen a solid answer and I don't own a VP so I can't tell you what the exact issue is.

[Mopar1973Man]

As for the solder issue, it was taken care of a while back.

As for the heat issue..I look at it this way. Take your laptop computer with you on a hot summer day with it laying in the back seat baking in the heat of the cab. 130-140*F inside. But the laptop is off and it can withstand that heat during storage. Now when you pull it out to operate it the room temp that is a milder 70-80*F, the laptop computer is happy and will operate a very long time. So like the VP44, it takes a heat soak from all the cast iron around it. Now when you fire it up and you hav 14 PSI or greater the fuel cools it down fairly quickly because the over flow valve is open and flowing fuel under the VP44 electronics.

The bottom of the VP44 PSG.

[JAG1]

Mike, you don't think the heat sink help in some small way even with the blower going?

[Mopar1973Man]

No... Because the chip inside the case has physical contact with the back side aluminum cover that has contact with the fuel. So like saying I pull in with a hot engine and put a fan blowing on it. Do you think all the parts that are surrounded by coolant are going to remain hotter longer? Sure... So just think of the fuel in this case being the coolant. So the stagnant fuel sitting in the pump is collecting heat along with all the other parts. I hard doubt a pelter cooler or blower is going to keep the electronics cool will all the barriers you got... If you want to keep the electronics cool don't shut off the engine, leave it running. As long as the engine is running the fuel is moving. Even BlueChip was going to build a lift pump timer to push fuel through, but it failed..there is no way to move fuel through the VP44 fast enough without the engine turning.

[ISX]

If the solder issue is fixed then what is it's issue with heat? The electronics are frying now? Seems like a triple redundancy for failure. I would like to see something on the entire history of how they are failing, theoretically or proven. The soldering issue being fixed was the first I had heard of it. Not having a 24V, I don't read hundreds of horror stories to find out what happened, but there is no reason someone hasn't made a writeup explaining the history of failures. All I have seen is 1679 or whatever the code is means the pump is dead, never anything further detailed. The temps do not drop quickly either. John's truck had 18psi and it still took a couple minutes for it to even start dropping. I think the fuel flow is just enough to soak up the heat that is soaked in from the engine given that the engine/pump were cold from the start. Once the pump gets hot from sitting there with no fuel flow, it is very hard to get the temps back down. They didn't even get under 120F I believe, it just doesn't have the flow to cool it back down once it gets hot.

[Mopar1973Man]

If the solder issue is fixed then what is it's issue with heat? The electronics are frying now? Seems like a triple redundancy for failure. I would like to see something on the entire history of how they are failing, theoretically or proven. The soldering issue being fixed was the first I had heard of it. Not having a 24V, I don't read hundreds of horror stories to find out what happened, but there is no reason someone hasn't made a writeup explaining the history of failures. All I have seen is 1679 or whatever the code is means the pump is dead, never anything further detailed. The temps do not drop quickly either. John's truck had 18psi and it still took a couple minutes for it to even start dropping. I think the fuel flow is just enough to soak up the heat that is soaked in from the engine given that the engine/pump were cold from the start. Once the pump gets hot from sitting there with no fuel flow, it is very hard to get the temps back down. They didn't even get under 120F I believe, it just doesn't have the flow to cool it back down once it gets hot.

Part of the problem is lack of good fuel flow. There is still goofballs out there running around listening to some other people about 5 PSI is great. Here is your heat problem. P1688 is a electronics failure code. Typically heat failure. Solder was part of the problem suppose to fix that problem with Rev 25 of the VP44. I tried looking up the rev numbers but no luck. Most of the failures now are still fuel pressure based and filter based. Either physically wearing the pump out or allowing the pump electronics to get hot. As for the solder failure I've not heard of one in a long time. As for the cooling ability of the lift pump is all based on how much fuel is in the tank and how warm the fuel in the tank is. So like today with winter weather heat soak in a mute point. But come summer its a important thing to consider.

[JAG1]

Thanks Mike for the details explaining this to me.Because of summer months then, getting the fuel filter housing isolated off the intake manifold is a good idea. That thing acts like a fuel heater when you don't need it the most, but, sub zero winter months would be benefit.Perhaps it is negligible value in discussing this... just don't know...... other than hearing all the issues with the vp caused me to do all I could for it. I'm still on the original vp perhaps borrowed time. Truck was built during the very last month of the second gen production line.

[Mopar1973Man]

Consider yourself lucky... I lost my first lift pump and VP44 at 50K miles basically... Since then I've been running on the 2nd VP44 with no signs of failure. I keep the fuel lubed up, keep the fuel pressure up, and keep good filters in the system. As for the fuel heater its disable after a certain temperature I want to say 70*F.So beyond that there is no magic to keeping the VP44 going...It just there is so many people abusing these pumps with low fuel pressure, dirty fuels, crappy filters, using dry fuels like kerosene, etc. Then they post up of how bad the VP44's are. It not the VP44 it the owners that abuse them.

[JAG1]

I see what your saying. I've kept up with the 2 cycle use, clean filters, two of them in line and always watched the fuel pressure. Although I've only been able to maintain a steady 14 psi all the time only because of the big lines and draw straw with stock pumps, my 02 runs smooth as glass, I need to try and keep my vp healthy. So afraid of the vp with all the bad reports, I even ran the return line into the fuel filler neck so the hot fuel returning would not be dumped right next to the drawstraw. My 92 developed a clogged tank vent so on the 02 I even installed an aftermarket tank vent all because of these reports. When installing the drawstraw I even cut out the intank screens for better fuel flow in case they clogged up.Oh well.... lots of work for little gain perhaps but, I go down the road knowing I did what I could. Next is the right aftermarket lift pump very soon. I would like to see somewhere around a steady 18 psi.

[Mopar1973Man]

Here is my pressures as of last summer...

http-~~-//www.youtube.com/watch?v=grl72Up-8T0

But now if I wonder over to CF.com and look around I'll find post where guys have install a brand new AirDog 165 and getting fuel pressures starting as high as 23 PSI and pull it down to 11 PSI. Pressure fall sure still be only 2-3 PSI for a good fuel system anything above 5 PSI is a serious issue.

This why I have a problem with Dodge and the test idle pressure only and pressure doesn't mean anything on volume. So what happens if you setup like this guy? (AirDog 150)

http-~~-//youtu.be/NB8o24rw1eU

Then there is some performance pump rebuilder out there making statements of "(Un-named) proved that 5 PSI, under load, made all the horsepower the VP44 pump could make, even with stock fuel lines, fittings and supply pump." and people now think that VP44 will survive at 5 PSI now because of this 1 shop making this claim on a dyno. There is no other statements made about longevity.

Then you got all the fuel additive market out there selling snake oil claiming to clean injectors and boost MPG and HP. Most of this stuff does nothing...

Then you have the owners that are cheapin' out and using cheap fuel filters, stock lift pumps, no fuel pressure gauge, dumping in tons of fuel additives and get fuel from there red dye farm tanks and wonder why the VP44 fails in less than 100K miles. Geez I wonder...

[anoldbiker]

Ok, I'm a little confused. The start of this was getting better MPG with cooler or hotter fuel. But it still comes to mind that when the liquid is injected in the cylinders it is in a somewhat vaporous form. In a split instance it is compressed and ignited. If this hydrocarbon was say 50 degrees cooler or hotter, what would a few degrees matter ? It's there a split second and gone. What energy is there is now gone. Are we talking about all the satellite equipment and the need for cooling / heating to maintain a specific temperature range. Not allowing a vapor lock prohibiting flow or tearing the associated satellite equipment apart ? I'm still not grasping.

[Mopar1973Man]

Thanks anoldbiker...I personally don't think there is any difference in hot or cold fuel for MPG's. I think the MPG factor comes from how well the pump is maintained. Because right now I'm holding a set MPG number for the most part through the winter and through the summer.

[dripley]

Mike gets a little touchy about vp's. I dont blame him after seeing exactly what he is seeing and people bad mouthing the IP. I think for just normal everyday driving and calculating mpg on a tank your fuel temp would have to go to an extreme to make much differance. Now if you are counting every .10 or .20 over the life of the vehicle it could add up to a nice chunk of change. But unless you are putting tha money back to cash in on it after 10, or even 20 years it is not going to make much differance in your pocket. Just my humble opinion.

[JAG1]

I know we got off topic a few degrees :lmao:But, Mike is right.... that last video!!?? That guys got serious disease.... banjo bolts, small fuel lines, too slow of a tank vent, clogged screens. Add that he's probably added some power mods, It's like trying to make some poor ole' guy run the marathon with clogged arteries.About cooler fuel... I think Mike is right again since he's got that accurate miles computer... he is seeing very little effect on mileage, but, If your combining hot fuel with colder air doesn't that affect how efficient the intercooler is working? Sort of like one affecting the other?

[dorkweed]

I really don't know either way. I do know that my truck usually gets better mileage in the warmer months. Mostly due to winter fuel, denser air(to drive thru), thinker fluids and less efficient combustion in COLD weather.My overhead "lie-O-meter" registers about 3mpg less this time of year.............even if I get the almost the same amount of miles at say 1/2 tank that I do in the warmer months. But when I fill up, I almost never get over 550 miles this time of year. Somethings going on that I can't figure here. My mileage this time of year is usually down to about 17mpg in combined empty/towing around suburbia. Normally it's around 18-19mpg in the warm months with regular diesel doing the same driving. But that's with Grandpa type driving............I'm not ina hurry.It's probably 80/20 that I drive to SE MO to snow goose hunt this weekend. Be a little over 1000 miles round trip. I'll post mileage figures when I get back.............now that I can post again!!!!!!

[JAG1]

Same for me too.... I see mileage variations I cannot explain. The intercooler must be a lot more important for mpg than for a fuel cooler. I know the older ctd's had less hp without intercoolers.BTW, I was down at Source Automotive today. Rip the owner says they've had 4 trucks come in with clogged tank vents. He might of said quit a few.... can't remember now. He said you can just see the fuel tanks collapsing. So watch your tank vents too. I would bet a lot of them are marginal at best. He he....Put a whistle on there, after a run if you get out of the truck and still hear it whistling you got a problem. I actually found it on my first gen, I could hear a hissing sound every time I pulled the fuel cap.