Plastic fuel filter with EFi - safe or not?

I would certainly buy the proper part, don't even consider fitting a plastic one, unless it was designed for the job. I have known of even the metal ones to split.

snipped-for-privacy@spamcop.net (Andy Hewitt) wrote in news:1gy1ioq.fqfy4kk1jg3eN% snipped-for-privacy@spamcop.net:

Thanks for that, Andy. I'll be sure to complain about being given the wrong one. Unlike many cars, this fuel filter lives in the engine bay. Imagine if I'd fitted the plastic one and it had burst, spraying petrol over the hot engine!

Indeed. As a rule, carb systems run at no more than 1 Bar, but injection (on indirect systems) can be as much as 5 Bar. Not only that, but older systems, with a mechanical fuel pump, might even have negative pressure.

Modern direct injection systems can be anything up to 2000 Bar (that's not a typo).

Ouch!!! 29000psi...

(And yes I did have to go check with the Bosch website before I believed it wasn't a typo!!)

It would be possible to make an injection filter out of plastic. On my car, some of the fuel lines are indeed plastic. Then there are the 'rubber' hoses to connect to the injectors.

The pressure isn't *that* high - only perhaps 2/3 times or so that found in the cooling system, where plastic is common in some modern cars.

However, you're right to want the correct replacement.

Crikey. ;-)

Yes, and it's the same on petrol and diesel systems too.

These are reinforced though. Even so, there was a known issue on BMW bikes where the filter casing would split, despite being in-line in rubber hoses. This was simply brought about by stamping the part number on, later ones were printed. Fortunately these were located inside the fuel tank.

Of course the volume of fuel under pressure is much less in the pipe than in the filter, the surface area under stress is massively different. A single square inch in the pipe is not as concentrated as on the casing of the filter.

It's enough, a carb model may run at 1 Bar (about 15psi), but even a modest injection system may run at 40psi. That's only if you use an electric fuel pump on the carb too.

Over the tens of thousands of miles that the filter is used, the extra stress could be critical.

Indeed.

over the hot engine!

That's essentially the issue, The stress n a thin walled pipe or filter = pressure x radius / wall thickness, for a filter the pressure is the same but the radius is 10 times larger & 20mm thick plastic walls would be expensive.

thats the injection pressure on a common rail diesel, not an EFI petrol! (which run at around 45-50psi max)

Tim..

Go check again.

Exactly.

I've not seen a non direct injection petrol system that runs at over

Duncan Wood ( snipped-for-privacy@dmx512.co.uk) gurgled happily, sounding much like they were saying :

That's why Andy specifically said "direct injection"...

They don't pressurise the fuel filter though.

Even on direct petrol injection engines (FSI, GDI, Fords HPI etc etc) the charge pressure - i.e. that supplied by the electric pump in or near the tank, pressure is less than 60psi. There is no user replacable fuel filter in the high pressure circuit. (i..e after the secondary high pressure pump)

Tim..