petrol tank noise

[ridgeback]

has anyone heard a thump kind of noise after the pump has primed sounds like the tank expanding 98 chim

[K3NJW]

Yup ... my 94 Chimaera used to do that. A noise like a metal tank expanding.

[tvrbob]

ridgeback said:

has anyone heard a thump kind of noise after the pump has primed sounds like the tank expanding 98 chim

Yes this is normal. As the petrol is drawn from the tank the large flat walls are known to flex giving a thump sound. You may notice when you take the filler cap off there is a sound of air rushing in.

[Big Al.]

Could be the old tank expansion Clunk! When you undo petrol cap very slowly do you hear and ingress (hiss) of air?
If you do loosen off your petrol cap to mid position, and see if the clunk goes away. If it does, then do the trim the washer mod on the petrol cap.

Have a search, if you can’t find the mod if you need it get back to me.

Hope this helps.

Ed to Add "Snap tvrbob"


>> Edited by Big Al. (moderator) on Tuesday 24th June 16:55

[shpub]

The trim the washer mod is not a good idea. The system is meant to be sealed and vented through a carbon cannister so that it meets the emission requirements, and so in the case of an accident you don't get fuel spilling out of the tank or under high cornering forces! TVR fit a special roll over valve to close the venting if necessary - cutting that washer basically makes all this a waste of time.

Some pressure in the tank is normal. If the tank is banging frequently, check that the pipe vent is not blocked or that the carbon cannister is not blocked.

Steve
www.tvrbooks.co.uk

>> Edited by shpub on Tuesday 24th June 17:18

[chimyellow]

My 95 Chimarea also does the clonk thing with the tank, but this sounds worse when there is less petrol in it. It is due to the shape of the tank (being wide and fairly flat and therefore easily deformable).
I also get the hiss but this is no more extream than on a number of other cars that I have owned (including a Renault that only had delivery milage on it when it arrived).

Just say that it is the boost charging if anyone comments.

[wildego1]

Steve,
I really did notice an improvement in performance after cuttting the washer. O.K. may upset the tree huggers but I think it's fair to assume that they already hate our guts for driving thirsty motors anyway.
Also should I manage to turn it upside down I cant help thinking that a ton of car on my head would be my only and probably final concern Oh and why fill the tank before cornering like a nutter. I usually only go halfway to reduce weight anyway.
If its obvious that I dont know what i'm talking about
please correct me.

[ridgeback]

where is the carbon canister i will check it thanks steve

[shpub]

wildego1 said:

Steve, I really did notice an improvement in performance after cuttting the washer. O.K. may upset the tree huggers but I think it's fair to assume that they already hate our guts for driving thirsty motors anyway. Also should I manage to turn it upside down I cant help thinking that a ton of car on my head would be my only and probably final concern Oh and why fill the tank before cornering like a nutter. I usually only go halfway to reduce weight anyway. If its obvious that I dont know what i'm talking about please correct me.

If you notice an improvement in performance then it is either coincidence, or your pump is on its last legs and needs all the help it can get or the venting system is blocked for whatever reason. Cutting the washer cures the symptoms and not the fault. It's like severing you nerves when you have toothache: stops the pain but getting a filling or removing the tooth is a preferable.

Cutting the washer is a bodge basically.

As for fuel not spilling... because of the design, it is quite possible even with a low tank to get fuel upto the top of the tank simply by cornering and the car doesn't need to be completely over for fuel to leak out. Seen a few cars that leak fuel when they shouldn't. I got pulled up in 520 leaking fuel out of the vent when there was only 5 litres or so in the tank. I had to fit a special valve to solve the problem. The 3000M series cars have the equivalent of a cut washer and most of them have to gaffa over the petrol flap because of the fuel leaking issue.

The carbon cannister is in the front of the rad or in the front wing.

>> Edited by shpub on Tuesday 24th June 21:17

[wildego1]

Oops, looks like I need to get a new washer and try and find the carbon cannister and I shall check the pump too.
Thanks for the clarification Steve.