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Fuel tank foam/sponge.

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Apart from the primary job of absorbing rainwater and then petrol from the resultant rust induced leak, what's the job of the foam on the top and bottom of the fuel tanks? Is it purely some sort of resonance/drumming reducer? It doesn't seem to be needed as a mounting protector as the tanks appear to rest on the seams (which are protected by their own rubber strip).

Is there some blindingly obvious reason for the sponge/foam to be there that I just haven't realised?

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Mine don't rest on the foam, they rest on the seams via a rubber strip, similar to a door rubber. Also the wooden panel (where the ecu etc is bolted to) can be 'adjusted' to give more downwards clamping force, again pushing on the seams.

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It's there to dampen noise and vibration, the tanks 'boom' when fuel sloshes about. The tanks are also pretty heavy when fuel so the foam acts as a dampener for any vibration from the car or themselves as fuel moves them about or oscillates inside.

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88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

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use *Styropor [TM] -type of foam instead, it is compressible enouigh to form an bed to sit in for the tanks. This type of foam is from the 'closed cell' type of thing, easy to cut and available in various dimensions.


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to name the things if I see them, that's what I call integrity..

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Its a crap solution either way. As Advantage states, they retain water and rot the tanks. Pooooooooooooooooooooooooor designo.


Caught between a rock and a hard place in a catch 22 situation, So its 6 of one and half a dozen of the other. Your damned if you do, but your damned if you don't so shut your cock!!!!!!!!!!!

Lotus Espirt Turbo S3    

Lotus Esprit S4 

Lotus Elise S2 Sport 130

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So can I assume an alternative such as Dynamat would be a superior (and less water retaining} solution to reduce any unwanted resonance?

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Yes :)


Caught between a rock and a hard place in a catch 22 situation, So its 6 of one and half a dozen of the other. Your damned if you do, but your damned if you don't so shut your cock!!!!!!!!!!!

Lotus Espirt Turbo S3    

Lotus Esprit S4 

Lotus Elise S2 Sport 130

pig_zps6d7342f1.jpg

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I honestly can't see the foam doing ANYTHING about the tank resonance or booming.

The tacky sheets of whatever it is, stuck all around the perimiter of the tank, I wholy agree thats what it is designed for, but the foam just wouldn't do anything at all. Its not a firm enought fix and its not the correct type of material to do that kind of job.

Do you have photos of the rubber lip you've got dudes?

I know on my car its just there to bed the tanks in and to stop any possible movement whatsoever, the bottom piece aids the squashig against the moulding webs in the lower tub, and the upper piece is just to squash between the upper of the tank and the plywood board. If it wern't there it would move and rattle something cronic no matter how hard you pushed down the plywood. Rubber door trim on the tank edges would wear away I'd guess, maybe it was a later added extra (an additional measure) cause none of the early cars had it, its just foam for us oldies and for the early Stevens cars.


Chunky Lover

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Simon, the rubber trim is nothing more amazing than a door rubber type of trim. It secures onto the seams of the tanks in the same way a door rubber clips onto a door frame.

The sponge has no contact with any part of the bodyshell or the wooden 'lid' as the seam/trim combination is taller than the sponge and thus the sponge cannot contribute to the rigidity of the tank's mounting.

Hence my query as to what it's actually for and my reluctance to re-fit it.

I guess the cars just got better and better with each model evolution...:D

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LOL

Maybe Lotus just forgot to not bother fitting it?

IT really can't do anything for resonance or booming, in most cases I've seen it almost falls off when the tanks are removed. If it was a bitchumin board (whatever it its called) backed then you have a chance of it doing something, but its not... Its foam, 'barely' held in place with glue, no backing and thus no possiblility of it reducing anything except the tanks ability to hold petrol....

If they don't touch the wood or the webbing then don't bother refitting them.... If your worried about booming then dynamat may well be a good way forward...

If the foam wasn't in my car then the sides of the bodywork would be covered in gel coat cracks! :)

Edited by Simon350S

Chunky Lover

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I got my information from 'a man who knows about these things'. I'm sure if I asked him if dynamat was a suitable substitute then he'd agree, so long as it's closed cell and waterproof. :)


88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

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TBH Bibsy, I was kinda hoping our friend who knows everything would offer you a comment on this matter.

Tell him 'thanks'. :unworthy:

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There was a lot of detail here on using a doormat a few years ago.


DanR

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Aly roof flashing is cheap substitute for dynamat


Amateurs built the Ark

Professionals built the Titanic

"I haven't ridden in cars pulled by cows before" "Bullocks, Mr.Belcher" "No, I haven't, honestly"

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I bought some closed cell foam stuff from halfords - the stuff you put ontop of toolboxes for padding. At £3 a sheet, I thought it was worth a go. It cuts well, is fairly firm but with enough give to allow it to be squashed when the tanks are secured.

There was no rubber trim on my tanks (1986 S3) and, infact, even the base foam was in good condition, just stained from where it was exposed.

DSCN1710.jpg


"Intellectuals solve problems; geniuses prevent them." Albert Einstein

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The faded bands on the picture above are the only point on which the foam makes contact with the floor of the body. 

 

Is there any new thinking on the redundancy of the foam these days? I am about to install my new fuel tanks and frankly don't see the point of the foam at all, top or bottom. I'm tempted to fit them with no foam, and maybe just a rubber strip around the edge of the bottom of the tank so it doesn't bang or dig into the fibreglass.

 

If there's any new and improved way of fitting the tanks with or without foam anyone has come up with would love to hear it.

Edited by Freemason

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I've recently fitted new alloy tanks, and clad the tops and bottoms of the tanks in self-adhesive, 10mm thick, closed-cell sponge. The sides are clad in self-adhesive heatshield material, so they are completely insulated. I did this so that the fuel temperature is kept as low as possible. I also made some new plywood tops for them, and once bolted up, I can hardly move them at all. The tanks appear to be solid, yet resiliently mounted.

 

The original foam on my old tanks was glued on, full surface, both top and bottom. It compressed once the plywood was in place, cushioned the tanks, supporting them, and keeping them away from chafing any GRP.


Margate Exotics.

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The foam was probably only to keep the steel tanks from making an oil can sounds when fuel sloshed..

 

Remove all rust.

I coated mine with a protective layer of a phosphate based primer.
Spray primer
many coats of paint
 

Then I coated mine with a thick truck bed liner paint
 

I also protected the rim edges with a rubber U-channel that I sealed with RTV. Since it is the metal edges rubbing on the fiberglass that scratches off the paint and allows the edges to rust first.

I made new foam pads with a closed cell foam, and covered that with plastic.

I also placed rubber tread mats under the tanks to keep them from rubbing on the fiberglass.

Oh and I coated the insides of the tank with POR-15 fuel tank coating.


Travis

Vulcan Grey 89SE

My Lotus Photo and Projects Album

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I believe the Americans have a phrase that goes "parts left out cost nothing". Which translates to they wouldn't have put it there if it wasn't needed cos it costs money.


Margate Exotics.

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Is there anyone that knows the dimensions for the fuel tanks?  I have an 88 and was considering replacing the old tanks with modern fuel cells.

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Had a look at my tanks from underneath today - saw the foam - cut out where it's just flapping about....

They look really good and clean - there is some slight and I mean slight surface rust in a couple of places - but it's very slight.

What do the tanks look like when they are completely shagged??

I'm sure mine will need replacing but would like to,figure out when I need to plan to do so.


Only here once

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Ian, you mean like the way they left out rust-proofed tanks? :P

Sorry, I had to.

Here's some pictures of completely shagged tanks Barry, from a friends Esprit. They always look good from beneath, but lo and behold! Note the holes around the edges of the tank in the first photo.

post-14356-0-44551000-1428986053.jpg

post-14356-0-88262500-1428986079.jpg


Vanya Stanisavljevic '91 Esprit SE | '91 Elan SE | '97 XK8

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Vanya

Thanks for shattering my eternal optomism,,,,,


Only here once

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