Overheating Fuel Tank. (Long!)

["therealdmcvegas" <DMCVegas@xxxx>]

--- In dmcnews@xxxx, "Walter Coe" <Whalt@xxxx> wrote:
<SNIP>
> The best cure, obviously, is to keep the fuel cool. The easiest 
place to
> start is reducing the heat transfer from the coolant pipes. As 
you may
> already know, aluminum is an excellent conductor of heat. And 
there isn't
> much room for insulation between the pipes & the fuel tank. I 
suggested
> before that an easy improvement would be to replace these 
sections of
> aluminum pipe with long pieces of silicone hose
<SNIP>
Yes, I figure that it is the coolant pipes that are heating the tank 
up. Another member off of the list did reccomend to me trying the 
exhaust wrap for the pipes. So this too is an option that I'm 
looking into. I really don't want to replace the existing aluminium 
pipes with rubber hoses. This just worrys me in as it's two more 
items that I have to worry about rotting/replacing in the years to 
come.

<SNIP>
> > Now, from all this, I have determined the following:
> > 1. A noisy fuel pump isn't always due to a collapsing fuel 
pick-up
> > hose.
> 
> You got that right! I installed a spring in my hose, too, and it 
seems to
> only make the problem worse -- by conducting the sound 
better and by
> producing more restriction/turbulence.
<SNIP> 
Add to this the fact the spring is yet another component to be 
installed. I stand behind it in as it is a fix that can keep the fuel 
hose from collapsing, but it is not what I would consider a 
permanent solution for my issue. I'm currently working on a way 
to not only remove the spring from the equasion, but the entire 
pickup hose as well. The less parts, the better, and I'd like to 
remove the main source that started this problem in the first 
place.

<SNIP> 
> > 2. Air flow from the front radiator is NOT heating the fuel. 
When I
> > stopped the air flow, the noise became worse. It wasn't until I
> > restored air flow that there was a sign of cooling.
> 
> This contradicts what I've read about installing an air dam. I 
would like
> to hear more about your theory here. I have found that once the 
fuel gets
> hot enough to cavitate, it stays hot for a long time.
<SNIP>
I have thought about this, and have come up with a couple of 
theories: 1. Air flow is what is sufficient to cool the tank down. or 
2. The coolant pipes on both sides of the radiator are transfering 
heat thru the fuel. Gasoline is absorbing heat from the source 
pipe, it then travels thru, and is reabsorbed by the cooler return 
pipe. While parked, the tank absorbed heat from the hot line, but 
was unable to lose the heat fast enough because cooler pipe 
had no water flow to carry the heat away. But once I drove a 
couple of miles, the temperatures recooled to the "balanced" 
level they were at before.

Now, to add to this, another possibility that has crossed my 
mind: Does heat directly transfer from the water pipe into the 
gastank? Or, is the heat absorbed thru the plate below 
protecting the gas tank? If the bottom plate is absorbing the 
heat, this would make total sense! Heat being transfered thru 
would turn the sheild protecting the gastank into a huge 
"hotplate"! And the reason that we would not see these same 
kind of symptoms in the winter is because the metal plate is 
able to transfer heat much easier than the composite material in 
the gas tank. Just like electricity, heat would transfer thru the 
path of least resistance, and would be absorbed by the ambient 
air flow under the car!

In any case, air flow from the radiator is NOT the culprit of hot 
fuel tanks. IMO, the DeLorean has one of, if not the best 
radiators for cooling the engine. Other vehicles typicly push air 
into the engine compartment, and it has not other choice but to 
exit out of the bottom of the car. With the DeLorean, hot air flows 
out thru each of the front wheel wells, as well as the bottom. Not 
just for the coolant, but the A/C always cools down quickly, and 
stays cold! Putting the air dam in place is not a good idea. It's a 
waste of money, it can cause vapor lock-up @ high speeds, and 
has no impact on the fuel tank at all. Only a VERY small portion 
of the top on the fuel cell is actually exposed to air from the 
radiator.

<SNIP>
> This thought has crossed my mind too. (briefly :-) I envisioned 
a fuel tank
> cover made of aluminum with heat-sink fins running the length 
of it. Then
> you would need a really big smear of heat sink compound 
between it and the
> tank. (Yeah, right :-)
<SNIP>
Don't laugh just yet, that may just be the thing we need. I don't 
know how we could attach fins to the bottom plate, but it should 
do the trick to rid the tank of excess heat. The only question I 
would have is how well does the compound adhere to things? If 
removal of the tank were nessisary in the future, You'd want to 
make sure that you could easily seperate the two.

<SNIP>
> Another thing to consider is using an inline fuel radiator. A 
nice spot for
> one would be in the frame next to the fuel accumulator, but 
there isn't much
> room for air flow through here. There is plenty of room in the 
engine
> compartment, but instead of stagnant cool air we have 
turbulent hot air.
<SNIP>
I don't think that a fuel radiator of any sort sould be nessiasry at 
all. Even if you installed one, I don't believe that it would allieviate 
the problem. It would cool the fuel behind the pump, and that 
isn't where the heat source is at. Rather than trying to keep hot 
fuel cool, let's keep the fuel from getting hot at all, and use the 
heat sink on the bottom to rid the gas of any stray heat that may 
have entered. Although if we insulate the water pipes, and 
remove the pickup hose to kill the noise, we may not even need 
to go to that far of an extreme with the bottom plate.

<SNIP>
> On a more sarcastic note, it almost seems a shame that they 
go to the
> trouble to plumb coolant from the engine to the heater core 
when they could
> have instead substituted hot fuel. All the heat you would ever 
need could
> be taken from the fuel return line. :-)
> Walt

I don't think that the engineers had thought of this problem of hot 
gas comming up. At least not in the kind of hot environments that 
our cars are in. It has to be the bottom plate acting as a heat sink 
in cold weather that keeps the fuel cool. Otherwise, Noisy fuel 
pumps would be a problem on EVERY DeLorean on the road.

-Robert
vin 6585 "X"