I ran a digital thermometer on my truck with the gauge mounted in the cab for nearly a year back in 02-03. The pick-up was mounted on the steel part of the fuel pump inlet.

The highest temperature I ever recordrd was 137*. That was an extended run in 100+ ambient temp. pulling a 32' travel trailer. I'd say the mean average with the truck at operating temps was 120. Slightly less in the winter.

I don't believe that a fuel cooler is necessary at all, and if you choose to run one it should be mounted on the feed line so that the angine can make use of the added power.

Adding a fuel cooler to the return line is akin to pissing on a forest fire....It makes you feel better, but really doesn't accomplish much.

Just my opinion, FWIW.

 

I've been running one for about a year now.....

 

Hey...bout time you got off that 'vette site for a few minutes.

Is yours mounted feed or return? How big of a difference did it make? ( I know you told me long ago, but I forgot )

 

Great analogy Cookie!
I agree with your points. Makes a lot of sense. Basic laws of thermodynamics and heat exchange. The feed line does seem the best spot for a cooler.
Nut

 

Scott, were you running a regulated return that passes fuel through the heads? Or was it the stock setup running fuel from the bowl?

 

Full flow, regulated return.

 

This will be my first full summer of testing. I installed the cooler late last summer and really didn't get the data I wanted.

So, the jury is still out on the need of a cooler IMHO. I can report that the fuel temps do get 150 plus degrees at the regulator (at least here in Phoenix) when ambient is 95 and above. Temperature taken at the regulator.

Did testing and recorded data at various fuel levels, coolant, EGT and oil temps. The cooler is mounted on the return line just before the tank. It drops the fuel temps about 20 degrees when running down the road, less while in traffic, etc.

No SOP performance or MPG gains to report. So far, just another peace of mind accessory. I have several months of very thorough testing with precision guages this summer. Real world data for what it's worth.

 

I believe the return line is a better place to mount the cooler. Think of it this way. You fill your tank at the station, assuming the fuel is out of a underground storage, the ambient temperature is in the 80's. The fuel should enter the tank somewhere in the 50's* fahrenheit, it gets pumped through the cooler, but because the ambient temp is higher than the fuel, your fuel cooler just became a fuel heater. Your fuel cooler will defeat it's purpose until the entire tank is heated to a higher than ambient temperature. Heated fuel is returned to the tank at whatever the engine exit temperature is, warming one of your largest heat sinks (the cool fuel in the tank) quicker.

Same scenario, only the cooler is in the return line. So the fuel comes out of the engine at whatever temperature (say 200* or even 150*)and goes through the cooler where it immediately looses heat to the 80* ambient air. Thermodynamics would lead me to believe this system should dissapate more heat, keeping the fuel in your tank cooler longer, and therefore feeding your engine cooler fuel.
In addition, if you live someplace that it gets cold in the winter, I believe you are going to increase the probability of gelling with a cooler on the feed side as opposed to the return side.

 

If that were possible I would tend to agree, but there is no heat exchanger that would fit in the space available that has the capacity to remove that much heat.

Take Heatstroked example. He see's at best a 20 degree reduction. From there it dumps back into a black plastic tank that not only acts as a thermos to hold heat in, but continues to absorb heat right off the black top. That means his 130 degree after cooler temperature is already regaining heat simply by falling back into the tank.

IF the supposition that there is more power/better economy to be gained from cooler fuel is correct. Then the only place you could realistically mount the cooler would be up front in the airflow immediately prior to it being fed to the engine.

 

You make an excellent point here. Also one would need to remember that the cylinder heads operate at around 200 degrees F. and will reheat the fuel right back up before it gets to the injectors.

 

I wonder how much fuel flows back to the tank at any given moment? Probably sort of trickles. So with that premise in mind you won't be cooling a fuel line with a constant/heavy flow of fuel.

 

They move 30 gallons per hour so it's a decent amount of flow, even on the return. It all just pumps around in a circle, through the pressure regulator and back to the tank.
The injectors skim off only what they need from the flow of fuel.

 

Here are the temperature averages based upon mutliple trips, all tank levels, with ambient temps, coolant temps, etc. all taken into consideration. The sensors and temps are taken at the fuel filter bowl, regulator and post fuel cooler just before dumping back in the tank:

Fuel filter bowl:120 degrees
Regulator: 155 degrees
Post cooler:125 degrees

Ambient temp: 85 degrees
Coolant temp:190 degrees
Fuel: 1/3 tank to full

 

85* is optimum temp for diesel. I my experience with 3406E Caterpillar motors, the trucks without fuel coolers would not perform as well at higher temperatures. On the dyno the engines would loose approximately 1% hp for every 10* over 85*. On two trucks that I delt with that had the same specs,one with cooler one without, one consistanly ran faster on the hills and got better fuel economy. Installed a cooler on the second truck and picked up about 1.5 mpg. Considering we typicaly run only 5-6.5 mpg that was a huge gain. Coolers were mounted in front of the radiator before the pump and injectors and with properly treated fuel there was no problem with gelling in the winter. These engines by pass a lot of fuel to cool the injectors so in tank temps would run about 160* so the cooler was most effective before injectors. These are just some of my observations in large deisel engines and don't know if there would be the same results in the powerstroke if fuel was cooled before going to the injectors.

 

I guess I didn't state that very clearly. I'm not saying the fuel will be cooled to 80*, I'm saying it will loose some heat to the 80* air on the return side instead of gaining some heat from the air on the incoming side.