Re: [DML] Overheating Fuel Tank.

["Walter Coe" <Whalt@xxxx>]

> So, my guess is not that the fuel hose
> is collapsing ( there is a spring installed), but that the excess
> heat in the tank is causing the internals of the pump to expand,
> and thus grind making the sound.

My opinion is that the pump doesn't change tolerance, but rather the fuel is
more apt to cavitate when hot. According to Boyle's Law in this situation:
as temperature is increased, the pressure at which the fuel boils is reduced
to less than the vacuum produced in the pump. So literally the fuel is
boiling inside the pump due to high temperature coupled with low pressure.

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 -- the same type sold by the
vendors used to connect between the pipes. This might provide enough
insulation to cure the problem. If no one else tries it soon, I'll try it
myself eventually before I go to the trouble of making a new fuel tank from
stainless.

> 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.

> 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. A friend came over to
have me work on his car, and after the car sat for a while we went to work
in the fuel tank. Reaching in there reminded me of looking for a lost
thermometer up a horse's ass. :-) With gloves on everything feels the
same -- hot & squishy.

> So, now I have the
> following questions. I've seen ads that giving a ceramic coating
> to exhaut pipes helps to keep the heat inside of them, and
> reduces the heat in the engine compartment. Does this really
> work?

I suppose so, but I don't think it would work very well on the coolant
pipes. Gasses don't conduct heat as well as liquid. And I doubt they could
get that ceramic to stick to aluminum anyway. I wouldn't be surprised to
hear that they heat the exhaust systems well above the melting temperature
for aluminum to get the ceramic to flow.

> If so, can I expect the same results for the two sections of
> pipe next to the tank?

I have a better idea: try wrapping the coolant pipes in insulating tape
meant for exhaust headers. It would be cheaper & easier than having the
pipes ceramic coated. That would probably work as well or better than
old-fashioned asbestos cloth.

> I've no idea what kind of a reaction household insulation
> would have with high water temps and/or chemicals found in
> that region of the car.

Household insulation wouldn't work well at all because it works by
restricting air movement. To do this, large quantities of air must be
trapped in the material. There simply isn't enough room in our situation.
And compressing this type of insulation makes it far less efficient. An
alternative that I have considered is expanding foam spray insulation sold
at hardware stores under the brand name "Great Stuff". It is good up to
temperatures of 400F, and the coolant pipes don't get anywhere near that
hot. The main drawback is that this type of insulation needs space to work
well, and that is something we don't have here.

> Venting the tank to air flow is another entire possibility, but I have
> concerns about aerodynamics and compromising the integrity of
> the plate protecting the tank on the bottom.

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 :-)

If there is not a good way to insulate the pipes, then I'm going to have a
stainless fuel tank made that has more room for possibly larger pipes and
enough insulation.

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.

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. :-) I'm sure the yankees will disagree,
but come to Florida and we'll fry up some eggs on the sidewalk.

Walt