Engine/Transmission (1998.5 - 2002) Cooling the fuel to the VP...10k miles of observations

[keimmmo]

Several months ago, Bob Weis started a search for a way to reduce the temperature of the fuel as it entered the VP-44. I followed it with interest thinking it seemed like a good idea! But, when some one mentioned that they gained fuel economy by cooling the inlet fuel, I jumped in with both feet!!!



I have just returned from a 10k mile trip... over 4k towing my travel trailer. I have run in temperatures from the high 20s to 100 degrees. Before I give my observations, let me tell you what I have done to my truck.



First, I relocated my original fuel filter housing to an angle iron base on the frame... moving it slightly down and outboard of the original position. I did it for two reasons. One, it seems to suck a lot of heat off the head where it is originally mounted... making it a fuel heater. Also, since I planned to fun a cooler in front of the radiator, I would have a situation in which the fuel lines would go from the frame to the moving motor, back to the frame, and back again to the motor. By relocating the filter housing, everything is mounted solid on the frame until it enters the VP.



I made my own fuel cooler out of copper tubing with brazed joints. I couldn't find a cooler that fit in front of the radiator, so I made one. Texas Diesel did me the favor of taking pictures of my system and posting them on the original thread. I hope he can post them here as well.



I relocated my fuel return into the tank to the fill tube. While this modification stands to lower the fuel temps slightly, I did it mainly because I run a lot of engine drain oil in my fuel and I felt it would help better "mix the brew".



Relocating the fuel filter housing is the best single modification to lower the fuel temps!!! Some have left it in the original position and insulated it from the head with plastic washers. That would be a simple way to get a big improvement... but it will still move with the motor, which I wanted to eliminate. I also think you will get even less heat into the fuel if the housing is farther away from the head.



I have found that the fuel going into the cooler is about the same temperature as the outlet at temperatures of about 50 degrees or lower. Above that, there is a DEFINITE difference between the inlet and outlet temps! The outlet seems to be about the same temp as the front bumper at ANY outside temp!



I seem to notice a little more noise until the motor is warmed up well from about 50 degrees on down. From about 30 degrees on down, it NEVER goes away. I am not sure why it is noisier or if it is a bad thing.



I was sure I was getting better economy while towing after installing the cooler. To prove my improvement, I disconnected the cooler and ran several hours without it. The economy on the overhead computer dropped exactly 1 mpg!!! I hooked it up again and it recovered the 1 mpg. The economy without the trailer seems to be up about 2 mpg. This thing DEFINITELY helps the fuel economy!!!



One thing I really like about the system is that you can install it and forget it. There are NO moving parts! It was never my goal to have bragging rights to the coolest fuel entering the VP on the planet! I just wanted to make life a little easier for the VP by cooling the fuel... and gain some economy at the same time. I feel the modification is a great success!



I now welcome your thoughts and comments.



Steve Keim

 

[Walt-L]

Thanks for sharing these all important MPG findings. I personaly always thought that a frame mounted filter may have a slight edge in the ability to retain smaller dirt particals since the engine isnt vibrating the filter. As for a cooler, I once picked up a superbike oil cooler on E bay for nearly nothing. These small motor bike oil coolers would make excellant fuel coolers. Hope to see more possitive results along these lines.

 

[rweis]

One thing Steve did that I found important was to put a "burp" fitting in his cooler. What happens is:



You add a cooler which cools best if the hottest fuel goes in at the top, coolest out at the bottom. When I added my H7B back under the bed first I added it as a return cooler and fed it from the bottom where there was more air flow. Since the return does not require "air purge" there were no consequences of the entrapped air as it was vented back to the tank vent line.



Then I changed the configuration and replumbed it as a fuel cooler going to the lp/RASP pressurization system and ultimately to the VP44. I put the incoming tank fuel in at the top and the bottom was connected to the lp / RASP system. Well I found out that you can get fuel feed without much problem, BUT there is a fair amount of trapped air in the cooler. Lucky I run a RASP w/lp backup. It has been about 300 miles and I am still getting some (fairly small, 1 - 3 seconds) slugs of air into the RASP (17 psi) which has to process the air and the fuel psi drops to the lp turn on (10 psi) which runs until the RASP get the air through and brings the fuel psi back up to 17 psi. In my setup the lp gets its input from quite a different place than the RASP gets its input.



Early on sometimes the RASP would take maybe 30 seconds to process a slug of air. The lp backup protected the VP, but you sure watch it like a hawk while you are down at 10 psi.



What Steve said he did (in the other thread) was to put a purge valve in the TOP of the cooler so the air can be vented and the cooler can become solid liquid fuel. This is an important step to consider.



I thought I had the air out by taking a line from the VP input and running it back to the tank and running the lp for 15 minutes to purge the air. That did not get all the air out of the cooler. I now think the fuel came in the top of the cooler and filled maybe the bottom 1 inch or 2 with fuel, but there was air in the top 8 to 9 inches of the cooler panels (it is a flat plate cooler). As I drive, the trapped air gets mixed with fuel and passes through the fuel lines to the RASP which then has to process the air bubble (RASP then generating 0 psi) and the hobbs switch senses the psi drop, turns on the lp which gives 10 psi (and I think helps to push the air bubble through the RASP) the RASP clears and back to 17 psi (hobbs senses the rise in psi, turns off the lp).



I think had I PUSHED fuel through the cooler, rather than SUCKED it through, I might have gotten more of the air purged. My cooler is right as the fuel lines come out of the tank BEFORE it gets to the lp/RASP presurization system, and maybe not as good an idea as Steve's that is AFTER the lp pressurization system.



HOWEVER an IMPORTANT POINT is to have a purge valve,



Bob Weis

 

[keimmmo]

Well, since we have things going here, let me admit to having to backtrack and modify my system a little to get where I am. At first, I put the fuel in the bottom and out the top to avoid the trapped air problem. I also ran a solid tank on the driver's side with a plug in the middle to make it into two tanks.



Although it helped cool the fuel, I could see that it wasn't as efficient as I would like. Dividing the tanks on the driver's side is quite important to separate the hot and cool fuel! Since heast rises, it makes sence to pull the coolest fuel off the bottom. But, I could see that the cooler would only fill about half way with fuel... with the rest being filled with trapped air. The air would greatly reduce the cooling ability of the cooler... besides the problem of air bubbles going through the system from time to time. Not only does air cause performance problems, but it does not lubricate or cool the VP and might do more harm than a constant source of hot liquid fuel. All that led to the separation of the tanks and the birth of the "burp valve".



I too had thought that mounting the filter solid instead of on a vibrating motor might make the filter more efficient... but thinking it through, it is the size of the holes in the filter media that determines the efficiency of the filter. I don't think the location of the filter makes much difference in how well it can do the job of filtering out crud.



A concern voiced on the other thread when I mentioned using copper tubing as a cooler was the potential for pressure drop due to the length of the plumbing. I have drilled out all fittings in the fuel system to a minimum of 5/16 ID... the same as the original fuel line. Everything is hooked up with 3/8 high pressure hose. Since the cooler has multiple paths for the fuel, it IS NOT restrictive. (Some ATF coolers WOULD be restrictive and reduce fuel pressure!) Eliminating the original fuel line and banjo fittings from the filter to the VP and replacing them with the cooler INCREASED my fuel pressure 4psi as cruise and 6psi at WOT!!!



Another point for my cooler is the price. If you can do your own welding and brazing, it is inexpensive to make. The total cost of all materials used to relocate the filter housing and make and hook up the cooler was under $50.



Steve Keim

 

[keimmmo]

I am wondering if any of you can tell me why the cooler improves the fuel economy. I know it does, but why?



Also, since others run trucks like mine in sub-zero temps, I assume it isn't possible to get the fuel too cool and actually do harm since I will RARELY see temps even as low as 25*. But, I have noticed the motor is more noisy below about 50* Is this harmful?



I welcome your input.



Steve Keim

 

[Hohn]

It appears to me that the cooler fuel has the effect of advancing timing. That would explain (or seem to explain) the louder rattle and the better MPG.



Now, HOW exactly a more viscous fuel would effectively advance timing is (sorry to say) beyond my expertise. I would theorize that the more viscous fluid is more easily separated into finer droplets, due to reduced surface tension.



That's my theory, anyhow.

 

[Cooker]

Also, since others run trucks like mine in sub-zero temps, I assume it isn't possible to get the fuel too cool and actually do harm since I will RARELY see temps even as low as 25*.

I think it is possible to have the fuel too cool. These trucks are equipped with fuel heaters that operate until the fuel reaches a certain temp IIRC that temp is 50 degrees.

 

[keimmmo]

Yes, the fuel heater! I was overlooking that in my thinking at the moment. However, I was able to keep both the factory fuel heater and water in fuel light hooked up when I relocated the filter. So, the heater will continue to function.



I haven't done it yet, but the way the cooler is made, it wouldn't be hard at all to hang a piece of cardboard in front of it in cold weather... making a kind of winter front. It will directly block the AC condenser, but not the trans cooler. At any heat that you would want to limit the air flow across the fuel cooler you won't need the AC anyway... unless it would effect the defroster.



I too an still learning, so more thoughts would be appreciated.



Steve Keim

 

[fox]

Cooller fuel is more dense. I have read that *80 is best for power and mileage with diesel fuel. I doubt the improvement is worth the effort though. But if it improves the life of the VP it would be.

 

[keimmmo]

I do not understand why, but my fuel economy is DEFINITELY up with the cooler... about 1mpg towing and 2mpg empty. (See the original post. ) I installed the cooler when fuel was over $3. 00 per gallon. At that price, the economy improvement will pay for the modification and improved VP life will be a bonus. The modification also improved my fuel pressure, and I'm sure that is a good thing.



Steve Keim

 

[Cooker]

Have you hand calculated fuel economy? I never really trusted those overhead things.

 

[keimmmo]

Yes, I always hand calculate the economy. The computer gives me a good idea of how I am doing, but is off quite a bit. I used it only as a reference to get an idea of the difference with and without the cooler.



On the trip from central Mexico up to Illinois, the ecomony never fell below 14 and hit a high of 17. 7 coming down the mountains... hand calculated. This is towing a 26 ft Nash with a big slide out. It is about 11. 5 feet high. I don't know the actual weight, but it is fairly heavy for it's size. The thing has a 10 inch I-beam frame under it!!! I had to put on 10 ply tires because the 8 plys just weren't handling the load!



The return to Mexico, I was HEAVILY loaded and had a head wind most of the way. Still, economy never fell below 12mpg... even the tank going over the mountains from near sea level and ending up 6000 ft above sea level!



I am thrilled with the ecomony of this truck! Everything else is pretty nice too.



Steve Keim

 

[csevers]

The Vp has a fuel temp sensor in it, you can see the fuel temp with a engine scanner(snap-on) so I am guessing that the ecm sees the fuel temp and adjusts timing acordingly, that makes the louder engine noise.



Have you tried to check the exact temp of the fuel?





Craig

 

[keimmmo]

I have no way to measure the actual fuel temp. Doing a touch test comparison between the front bumper and the outlet of the cooler, I would say it is very near OAT.



I do not have a scan tool or access to one. NOTE: I live in central Mexico! I am quite used to making do with what is available and often can not get the right parts or tools! I DO pride myself in being to make honest repairs with what is available... not "cob jobs". Not being able to even buy a commercial cooler led me to make my own. I hope to have pictures of it posted on this thread in the near future. Texas Diesel is working on the project for me.



A fuel temp sensor in the VP that would advance the timing makes sence. If there is someone along the way between Mexico and Illinois with a scan tool who would be willing to help do a little research, maybe I can stop by some time and we can try to get some real answers!



Now, I am wondering if a fuel cooler would help the old '92? I CAN'T IMMAGINE it has a fuel temp sensor in the pump!!! Although I do not own a 3rd gen, would it help them?



Steve Keim

 

[rweis]

I have a fuel temp sensor just prior to the Vp inlet.



I towed this weekend 100 miles one way. Fuel inlet was OAT + 30 degrees and I have a few "mods" working on keeping the fuel temp down. OAT was 80 degrees.



Bob Weis

 

[keimmmo]

Bob,



80 + 30 is only 110. You are getting pretty close to your original goal! Even if it isn't exactly what you wanted, it is still cooler than original! You have had a lot of discussions about actual internal pump temps. You are measuring the temp of the fuel entering the VP. It would be interesting to compare that to the INTERNAL temps as measured by a scan tool!



I wish I had a way to measure my actual temps. I know "It feels about the same as the front bumper" isn't very exact. But, I'm confident it is better than before I started.



I will NEVER see anything below 30* OAT down here. It was 54* when I started the truck this morning with an afternoon high of 75 degrees. But, for the chilly days and expecially for when I go up to Illinois, I think I'll cut a piece of cardboard to block the cooler and see how it works.



Steve Keim

 

[keimmmo]

HOW TO BUILD A FUEL COOLER



As stated in the first post on this thread, this thread was started to help those who are just getting interested in cooling the fuel to the VP since the original thread had become quite long and cumbersome. Bob Weis and I, as well as many others, continue to post on BOTH threads.



I have just posted on the other thread how I built the fuel cooler I am using. I have no idea how to link the threads, so I will just give information here for where to find the information on the other thread.



Pictures of my cooler can be found on posts #348 & #349 in the thread "Modifying fuel system so temperature input to VP44, 80*-100*, your thoughts" by Bob Weis. Instructions to make one like mine can be found in the same thread on post #355.



I welcome your questions and comments.



Steve Keim

 

[Gary - K7GLD]

HERE ya go Steve:



HOW TO BUILD A FUEL COOLER (See pics on posts #348 & #349)



https://www.turbodieselregister.com/forums/attachment.php?attachmentid=55192&stc=1



My cooler is made of 1/2 rigid copper tubing for the tanks and 3/8 flexible for the cross tubes. The cooler is 16 1/2 inches tall and 26 inches wide. It would be possible to go taller and/or add more tubes... just be careful that the tubes do not interefere with the studs that mount the AC condenser or trans cooler! To make it any wider would require a different mounting system than I have used.



You can buy the tubing any place where plumbing supplies are sold. I brazed all joints to assure good strength. Lightly sand all areas to be brazed... cleaning the copper makes it easier to braze. Make sure your joints seal and do not have leaks!!! Diesel will find the smallest imperfection and LEAK!!!



The passenger side tank is 16 1/2 inches tall. The driver side tank is made of two pieces 7 3/4 inches long with a 1 1/2 inch space between them... a total of 17 inches long. The pass tubes are about 25 inches long... I used 8 of them.



I recommend starting with the driver side tank. Plug the ends that go together in the center and braze a brace on them to make one long piece out of the two. I recommend plugging the ends in the middle first since it is very difficult to cap them after brazing the brace between the two pieces! Trying to work with two separate pieces is fairly difficult. If they are not braced together the finished cooler will be weak. I brazed oil galley (expansion) plugs that I had on hand onto the ends to make the plugs. Do not plug the other open ends at this time. It will be easier to clean out the inside later with the ends open! I put the brace between the tanks on the front of the tubes... but it has to be a small piece or it will hit the front bumper! Brazing it on the outside will block air flow. Brazing it on the inside is not an option since it will make it impossible to put in the pass tubes.



Note that the cooler needs to be mounted high enough that the upper inlet hose will clear the top of the trans cooler. It also makes it clear better and is easier to install the hose if you angle it slightly toward the rear! The inlet and outlet are just pieces of 3/8 tubing with a very slight flair on the end to better hold the hose.



Present the drivers side tank to the front of the trans cooler. Mark where you plan to put the cross tubes... making sure they will not hit the studs that mount the condenser and trans cooler! Drill the holes for the inlet and pass tubes with a 3/8 bit. The outlet can be any place on the lower tank... pointed straight outboard. I have mine in about the middle of the tank. Toward the bottom would also be fine. DO NOT put it in line with a pass tube!!! It will be VERY DIFFICULT to position both tubes so they will flow well!!!



Lay the passenger side tank beside the driver side tank and mark where to drill the holes for the pass tubes. Drill the holes.



I recommend brazing in the top and bottom pass tubes first. That gives you a frame to work with for brazing the rest of the tubes. It is also the easiest way to get everything square! Braze in all the pass tubes, the inlet and outlet.



You need four sturdy pieces of strap steel for mounting braces. Place the cooler in front of the AC condenser and mark where to locate the mounts. I used the two studs/nuts that mount the condenser as mounting points.



With the drivers side mounts in place, the cooler will hang in place so you can make and install the passenger side mounts. Use the holes in the AC condenser as mounting points. If you remove one of the screws in a factory mount you can see what size screw you need. I used "poor man's Loctite" (silicone) to keep the small screws from vibrating loose.



At this point you can clean the inside of the tanks the best you can and plug all open tank ends.



For the "burp valve" on the top of the passenger side tank I just built up several layers of braze over the expansion plug. Drill out and tap it for the valve... probably 1/8 NPT. My valve is from an old fuel filter. BE SURE the valve is rated for fuel!!! Some valves from radiators for example have rubber seals that will swell when exposed to fuel and leak!!!



When I first installed the cooler, I added a cheap 3/8 inline automotive fuel filter between the cooler and fuel pressure port. You WILL have some burrs and welding crud in the cooler that could damage the VP!!! I removed the filter after a couple of thousand miles and hooked the cooler directly to the VP.



This will give a good idea of how to make the cooler. Feel free to ask questions if there is something you do not understand.



Steve Keim

 

[keimmmo]

Neat! I knew there was a way! I can build a fuel cooler out of virtually nothing, but computers are another matter! Thanks for getting the information directly onto the thread.



Steve Keim

 

[keimmmo]

I have been thinking about csevers' comment about the fuel temp sensor in the VP and the timing being adjusted (advanced?) due to the lower temp. I have felt since installing the cooler that it has reduced the turbo lag, but I didn't want to really stress the point since I have no way to measure it. However, if the timing is indeed being adjusted by the cooler fuel, maybe it ISN'T my immagination!!!



Fuel milage is DEFINITELY up... I guess it would stand to reason that it is due to improved performance.



I still don't understand everything I know about the improvements the cooler has made. But, it certainly is interesting!!!



Steve Keim