Micra fuel tank leak

[DiyNutJob]

I am looking at a slow fuel tank air leak due to corrosion of the filler neck around the cap area. This caused the petrol to evaporate over the course of a few months. So far this hasn't caused anything to light up on the dash. According to some reports on the internet, the corrosion is an MOT fail. But, I have never seen a tester looking at the fill opening. Does the fail only apply when an indicator is shown on the dash? How do I assess how bad the leak is, perhaps with some kind of pressure measuring device? Would it be cheaper to buy a new neck than getting a testing device? An ebay china neck is about £35. Another possibility is for me to attempt to remove the bubbled up corrosion at the cap area. But I have no way to know afterwards if the leak is fixed.

Here's a video on neck replacement, and it doesn't look hard to do.

 

[Burnerman]

I can’t see any dash warning being applicable here, but replace the filler neck - any fuel smells should ring warning bells.
I believe the fuel neck has to be corrosion free and I’ve seen it checked once.
Mottie or Carman will know better than me.
John

 

[DiyNutJob]

The leak is slow enough to not produce a smell. The only evidence is petrol gone and rust bubbles at the cap area. Also dirt built up on paint around the filler door in a large patch. There should be a sensor to indicate a leak, i.e. vacuum pressure too low.

Google:
What does an evap fuel tank pressure sensor do?

It monitors pressure to detect evaporative leaks and loose/faulty gas caps that may be preventing fuel vapors from being contained in the EVAP system.

 

[Burnerman]

Basically, petrol fumes are burnt in the engine rather than being allowed to escape into the atmosphere.
If the leak is so minute, surely that wouldn’t affect your fuel consumption?
John

 

[DiyNutJob]

Well, a full tank of petrol gone with car not driven. That's pretty bad consumption.

 

[freddiemercurystwin]

Are you sure you weren't drinking it?

 

[DiyNutJob]

Are you sure you weren't drinking it?

Maybe I syphoned it for the petrol I wanted to buy for experimental cleaning of stuff?

 

[Burnerman]

Are we heading for another 30 page nonsense thread?
John

 

[DiyNutJob]

Nothing nonsense about evaporating a tank of petrol. Was full last Jul.

 

[carmanmemoranda]

I am looking at a slow fuel tank air leak due to corrosion of the filler neck around the cap area. This caused the petrol to evaporate over the course of a few months. So far this hasn't caused anything to light up on the dash. According to some reports on the internet, the corrosion is an MOT fail. But, I have never seen a tester looking at the fill opening.

Fuel cap has to be checked even before the test is started. If it is leaking, it can be refused to test, as per.....

Legislation permits testers to refuse to test vehicles in certain circumstances. If any of the reasons for refusal (see below) apply, you should not carry out the test and must return any fee paid for the test. You should carry out appropriate pre-checks before starting the test, to ensure the suitability and general condition of the vehicle.

If the vehicle presenter needs written confirmation of why the test cannot be carried out, you should register the test using the MOT testing service and issue a VT30 clearly showing the reason(s) why the test could not be carried out.

If reason to refuse ‘i’ applies, you should issue a handwritten CT30 containing as many of the vehicle details as possible. A copy of the CT30 should be retained by the VTS.

The reasons for refusing to carry out the test are:

1. a. The V5C or other evidence of the date of first use is not produced. Normally this evidence is only necessary if the vehicle has a ‘cherished’ registration mark (also referred to as personalised registration number) or if the registration mark’s year letter does not make it clear which standard should be applied.
2. b. The vehicle or any part or equipment on the vehicle is so dirty that examination is unreasonably difficult.
3. c. The vehicle is not fit to be driven when necessary to complete the test because of a lack of fuel, or oil, or for any other reason.
4. d. The tester considers a load or other items, or insecurity of a load or other items, would prevent a proper test being carried out - unless the load is secured or removed.
5. e. The VTS asks for the fee to be paid in advance and this is not done.
6. f. The vehicle emits substantial quantities of avoidable smoke.
7. g. A proper examination cannot be carried out because any door, tailgate, boot, engine cover, fuel cap or other device designed to be easily opened cannot be easily opened.
8. h. The condition of the vehicle is such that, in the opinion of the tester, a proper examination would involve a danger of injury to any person or damage to the vehicle or other property.
9. i. The vehicle has neither a registration mark nor VIN/chassis number or frame number by which it can be identified, or that all such identifications are illegible or use letters and numbers not normally used in the English language.

Does the fail only apply when an indicator is shown on the dash? How do I assess how bad the leak is, perhaps with some kind of pressure measuring device? Would it be cheaper to buy a new neck than getting a testing device? An ebay china neck is about £35. Another possibility is for me to attempt to remove the bubbled up corrosion at the cap area. But I have no way to know afterwards if the leak is fixed.

Here's a video on neck replacement, and it doesn't look hard to do.

If it was corroded that petrol would leak when being filled, or after filling or whilst being used then it should fail, as per....
and/or
If it was actually leaking before or during the test, then instant refusal to test, or fail as per.....

Defect	Category
(a) Fluid: (i) leaking excessively and likely to harm the environment or to pose a safety risk to other road users (ii) leaking continuously and likely to pose a serious risk to road safety	Major Dangerous

 

[DiyNutJob]

It can be opened easily. There is no liquid leak. Therefore it must be a pass then? It's an air leak that allows evaporation.

 

[Harry Bloomfield]

It can be opened easily. There is no liquid leak. Therefore it must be a pass then? It's an air leak that allows evaporation.

In the past, fuel tanks had open breathers. Fuel didn't evaporate out of them then, so I would doubt it has evaporated out of yours - more likely is someone has syphonned it, or you have used it.

 

[DiyNutJob]

In the past, fuel tanks had open breathers. Fuel didn't evaporate out of them then, so I would doubt it has evaporated out of yours - more likely is someone has syphonned it, or you have used it.

We can all agree petrol is highly evaporative.

 

[freddiemercurystwin]

Is it any good at cleaning stuff though?

 

[carmanmemoranda]

It can be opened easily. There is no liquid leak. Therefore it must be a pass then? It's an air leak that allows evaporation.

Can it, or does it, spill when filled or full ?