Hissing

[furtive]

My car hisses from the somewhere around the exhaust/backbox when I turn the engine off. Haven't noticed it doing it before and so I think it must have only just started to do it. What could be the cause, or TADTS?

[mondayo]

Make sure it's not coming from further forward. I thought mine was hissing in the summer and it was a rubber hose that had perished near the bulkhead, but then was coming out under the car. It was something to do with the cooling, as mine started to get a bit warm.

[mike9009]

mondayo said:

Make sure it's not coming from further forward. I thought mine was hissing in the summer and it was a rubber hose that had perished near the bulkhead, but then was coming out under the car. It was something to do with the cooling, as mine started to get a bit warm.

Agreed, it could be your heater hoses. Worthwhile after a longish drive (ensuring you do not overheat!) parking up on a clear bit of road and checking for drips underneath. Looking at the engine bay from the front of the car they run into the cars interior at the right hand side of the engine.

It is a relatively simple job to replace - even for a complete novice like me.

Otherwise, if it is something else i cannot help.......

Mike

[MX-5 Lazza]

Or it might be nothing. Do you have the standard airbox? Cold air kits tend to hiss while the engine shuts down.

[furtive]

It's definitely coming from the rear, nowhere near the heater matrix pipes.

And yes I have a standard airbox

[Farmboy UK]

Fuel filler cap. Mine hisses after any decent length drive if the tank is anything under half full.

Don't know if it's something to worry about but I wont let anyone smoke near it lol

But yea, it's loud enough to hear inside the cabin

[Farmboy UK]

dannyjohnson said:

It is highly likely that friction belt connecting the voice of the engine.

Huh??

[MX-5 Lazza]

I'm guessing that English is far from his 1st language and he's suggesting that the noise might just be belt noise. The belts can make a fair bit of noise, especially as most MX5s don't have any under-bonnet insulation.

p.s. your fuel filler cap shouldn't hiss, you probably need a new one

[furtive]

I'm pretty sure my belts don't make a noise when the engine is turned off

[MX-5 Lazza]

furtive said:

I'm pretty sure my belts don't make a noise when the engine is turned off

I'm just the translator!

Mine does hiss as it's stopping but I have a lot of rotating parts and a filter that amplifies the intake

The OP says the noise comes from the rear though so the fuel filler cap is a possibility. It really shouldn't hiss though as it should stay under pressure.

[furtive]

I am the OP

The sound seems to come from the drivers side at the rear - the fuel filler is on the passenger side

[Mr MXT]

Maybe you've ran over a snake?

[Farmboy UK]

MX-5 Lazza said:

I'm guessing that English is far from his 1st language and he's suggesting that the noise might just be belt noise. The belts can make a fair bit of noise, especially as most MX5s don't have any under-bonnet insulation.

p.s. your fuel filler cap shouldn't hiss, you probably need a new one

I feel rude now - I forget that the pistonheads community is large and international. Apologies for any offence.

Also, thanks for the advice Lazza, I think that may be a wise move. Before I do, is there some sort of fuel vent pipe that could be blocked thus causing this pressure/hissing?

[MX-5 Lazza]

The pressure is supposed to be there. It's supposed to stay there though as its part of the emissions control stuff.

[attym3]

Tank is suppose to be under pressure I think I started a thread on it here....

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Also this thread doesn't make sense, have posts been removed?

[MX-5 Lazza]

Yes they have

[Farmboy UK]

Cheers for the link to the other thread. This has 100% convinced me I need a new fuel cap. There is no way my cap should be hissing unless I have unscrewed it. If there is a vent, it is only supposed to allow air in and not vice versa.

[MX-5 Lazza]

Not that it actually matters. Like I said, it's to do with emissions control and the car will run quite happily without pressure in the fuel tank.

[furtive]

Update: Petrol tank was almost empty so I filled it up yesterday. It's stopped hissing so I assume that means my fuel filler cap is leaking?

[MX-5 Lazza]

Or you didn't have it screwed down all the way. Do you usually keep turning until it clicks?