Thoughts on fuel tank temperature?

I'm working on installing the fuel tank and fuel system. I had planned to install a closeout panel behind the tank, between it and the engine. I then started thinking about what kind of temperatures the tank goes through. With the engine right next to it, does the tank heat soak? Ultimately if you leave the car outside after running and it's 110F out, the tank is eventually going to warm up no matter what kind of heat insulation you have between the tank and engine.

How does the tank cool back down once you start driving? Should I consider adding some vents in the fuel tank compartment to help bring temps down once the car starts moving? I was thinking of cutting some holes or ducts in the floor to pull air in from beneath the car.

My initial plan was thermal barrier between tank and engine, sound deadener and thermal insulation all along floor and between tank and passenger compartment. I was also planning to direct some air towards the surge tank and fuel components.

Thoughts? Am I overthinking it?
 
Personally I would install a full closeout panel with reflective barrier (gold/lava rock sheets) between tank and engine (with 1/2"+ air gap) and call it a day. I don't think much radiant heat can get past that. The bigger heat soak issue classically has been cycling of the fuel through the injector rails and back which soaked up all the engine heat and brought it back to the tank. The LS style fuel system has solved that since it's return less only pulling fuel that it needs. The lift pump is another factor to think about since it's always running and it's heat could be pulled into the tank I would image that to be a much smaller source of heat however.
 

Terry Oxandale

Skinny Man
Supporter
My personal experience is that with my particular design, fuel tank temperature is more impacted by recirculated fuel than by conductive/radiative heat on the tank itself. As Mark noted above, this could be mitigated to some degree, but one person's gain may be another's loss in temp increases. I wanted cooler fuel to circulate through the system by taking advantage of the larger tank volume, but that works fine until the tank temperatures finally match those of the hose/fuel line temps at the engine.

In the end, I've fabricated thermal barriers around the surge tank, insulated hoses in the engine bay, ducted cooler air around the tanks and engine area, and eventually installed a 5" x 5" fuel radiator in one of the side scoops to cool the fuel just prior to the rails. The primary issue I had with any of the warm fuel was that the surge tank would begin boiling on hot days (95º plus, and during longer drives of 30 minutes or more), and that combination resulted in my high-pressure fuel pressure dropping significantly, which ain't good for fuel injected engines. Pressurizing the surge tank (I can close off the circulation at will) at the low-pressure side helped in an emergency to get the car somewhere, but not what I would do all the time. I've never dead-headed my LS2, but would only be concerned that the slower flow of fuel through the longer "hot" paths during street drives would raise the temps in those hoses quite a bit.

Eventually I think I've gotten everything sorted out. Just to give you an idea of what I dealt with, on the worst case days, my fuel tank fuel temperature (I work off one tank, and then transfer fuel from the other tank as needed) approached 170º, so you can imagine what it was at the surge tank, or fuel lines going to the rails.
 
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Terry - that is .... HOT!

Thanks for the input; I'll plan to go with my original thought (full closeout, sound damper, thermal barrier, and air gap. The two triangular openings on either side of the fuel compartment look juicy, I may leave those open to get some amount of air moving in and out.
 

Howard Jones

Supporter
Cam,
How about mounting a fan in one side of the "triangle" openings and getting some blow through venting. You could sense fuel compartment air temp to turn it on and off if you wanted to, but I think I would try and get a good idea just how hot it gets in there first.

My car uses a carb and has no other systems in the fuel compartment. The fire wall is completely enclosed and insulated and the interior air temp is pretty much the same as the interior of the car as you would expect. However with FI fuel systems creating all that heat I agree that it needs to be addressed.


Here's a good fan used for lots of motor sport applications.

Allstar Performance ALL13008: Heavy Duty Inline Blower Fan 3" Diameter | JEGS

More on fans,

http://www.allstarperformance.com/specSheets/pdf/1035.pdf

Here's a controller that might work for you. It very cheap so I would give it a try and see how it works.

W1209 12V -50-110degC Digital Thermostat Temperature Control Switch Sensor Module | eBay
 
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I agree with everything, and i will also be adding 4 naca ducts under the car at beginning of engine compartment to blow on turbos and front of motor. It may bring in more dirt though, so atleast use some type of screen.
For the fuel system, I used 2 pumps. Only one pump runs during normal cruise, and the second pump will only turn on after 5psi. This makes it so you have less fuel flowing, when you can't possibly use all of the volume of one huge pump. More volume= more trips through the fuel rails that ultimately is the component heating the fuel. Run your return to the swirl tank, and not back into the tank directly. This will further lessen heating up the large tank, and fuel will only make a few rounds through the rails before it is consummed. Combine that with putting the fuel lines in high temp sleeves around exhaust and motor, right up to the fuel rails. As one final though, a heat sink type cooler inline on the return line like Terry mentioned. I am expecting NO fuel heating issues at all.
 
There are some good (and not cheap) PWM fuel pump controllers that can allow you to vary the amount of fuel pumped by RPM. One of those would be helpful if you are spending a lot of time with the engine lightly loaded.
 
Thanks guys - I'm running an LS motor with a returnless style fuel rail. Aside from ambient and radiant engine heat, heat from the low pressure pump are likely to be the main sources of heat. I may go with a fan to help circulate air around the tank or just leave it. I plan to give the car a fairly good shake down before calling it "done" so may run a thermocouple down in there to get some measurements before making a final decision. Seems like it's not uncommon to grow up thermal block and call it a day.
 

Randy V

Admin
Lifetime Supporter
A number of years ago we discovered the loss of fuel via venting to the atmosphere in two of our race cars. Both running very high volume and high pressure Aeromotive pumps. The loss was bad enough where our fuel mileage was nearly cut in half. These cars used a return style fuel system - I have no idea how hot it was but suffice to say the cell was very hot to the touch.
A quick trip to the local auto parts store and we were installing heavy duty automatic transmission coolers in the return line as well as a pair of 12v bilge blowers we kept on hand for brake duct coolers. The problem was not totally solved until I extended the return lines inside the cells to run 1/2" or so from the bottom rather than just dumping the return fuel in at the top.
The cars were Corvettes racing in the Speed World Challenge series.
 

Terry Oxandale

Skinny Man
Supporter
Interesting comment Randy. I've often thought I should be getting better mileage than I do, and your post seems to indicate that, given the volatility of warm gasoline, venting off a noticeable volume of fuel as vapor, seems plausible.
 

Randy V

Admin
Lifetime Supporter
Interesting comment Randy. I've often thought I should be getting better mileage than I do, and your post seems to indicate that, given the volatility of warm gasoline, venting off a noticeable volume of fuel as vapor, seems plausible.
Well considering that the fuel pump was moving more than 2x the amount of fuel than the engine could possibly consume even at max power, there was a considerable volume coming back off the hot fuel rails that was quite literally sprayed into the top of the cell - it was a problem.
 

Cliff Beer

Supporter
Highly recommend the fuel cooler/radiator idea Terry mentions - have used that before with good effect.

Keep in mind this is fuel flowing through, so, there needs to be appropriate protection against puncture by stray rocks and such. There are coolers which don't employ the traditional radiator type construction with thin walled conduits, but rather thicker walls. Just for example, the porsche brass 28 row oil cooler is one such cooler.
 
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