tr6tuga Posted July 16, 2022 Report Share Posted July 16, 2022 Good evening wise fórum. Formaly in my 1971 tr6, I could ear petrol coming back from MU INTO the tank , on idle. For No apparent reason it Started to leak along the return pipe to the tank where ruber replaces cooper, even when circlips were set... It looks that I have a strong pressurized fuel return. Try to blow all the way and there is no resistence Petrol cap os original, makes no diference when open Where to look ? Thankyou Quote Link to post Share on other sites
Mike C Posted July 16, 2022 Report Share Posted July 16, 2022 I'd have a hard look at the rubber pipe for porosity. If it's in any way suspect, I'd replace it. Quote Link to post Share on other sites
Waldi Posted July 17, 2022 Report Share Posted July 17, 2022 My MU return line started leaking as well on the short rubber 3/16” connecting pipes; they were not suitable for fuel, it appeared. The hose was marked with “suitable for unleaded fuel”. The rubber hose was just 2-3 years old and I had ordered these from a supplier in the UK. That’s when I decided to dig deeper in the required type of fuel hose for our cars. FWIW: The return flow from the MU is just a dribble on my car. The return flow from the PRV is much more. Waldi Quote Link to post Share on other sites
tr6tuga Posted July 17, 2022 Author Report Share Posted July 17, 2022 Good lead try to source new rubber hose etanol resistent Quote Link to post Share on other sites
Waldi Posted July 17, 2022 Report Share Posted July 17, 2022 Gates Barricade and Cohline have an ethanol-resistant grade (Cohline has several). Here is the Gates hose from Moss: https://www.moss-europe.co.uk/fuel-hose-gates-barricade-ethanol-proof-3-16-id-per-metre-gfh1018x.html Waldi Quote Link to post Share on other sites
CP26309 Posted July 18, 2022 Report Share Posted July 18, 2022 Thanks for sharing that, I just ordered it for mine, many years ago (in the leaded fuel days) a garage replaced my rubber return drain with an incorrect rubber pipe which popped off causing an engine fire! Which in turn taught me the lesson to always carry a BIG fire extinguisher! Quote Link to post Share on other sites
tr6tuga Posted July 18, 2022 Author Report Share Posted July 18, 2022 What a great fórum we have, sharing is all about Quote Link to post Share on other sites
Jonny TR6 Posted July 20, 2022 Report Share Posted July 20, 2022 (edited) On 7/17/2022 at 4:21 PM, Waldi said: Gates Barricade and Cohline have an ethanol-resistant grade (Cohline has several). Here is the Gates hose from Moss: https://www.moss-europe.co.uk/fuel-hose-gates-barricade-ethanol-proof-3-16-id-per-metre-gfh1018x.html Waldi Worth noting that this is only suitable for return from the MU and carb cars. The pressure rating is only 50PSI whereas anything post pump, up to MU should be able to handle 110PSI+ Spoke to these chaps and this is what they recommend for post pump application. 10 BAR is 140PSI so more than adequate https://www.thehosemaster.co.uk/r9-unleaded-petrol-diesel-ethanol-automotive-fuel-hose Edited July 20, 2022 by Jonny TR6 Quote Link to post Share on other sites
stuart Posted July 20, 2022 Report Share Posted July 20, 2022 For post pump piping I prefer to fit this R14 hose which is a higher spec and will even cope with Methanol or E85. Gates R14 Stuart. Quote Link to post Share on other sites
Jonny TR6 Posted July 20, 2022 Report Share Posted July 20, 2022 7 minutes ago, stuart said: For post pump piping I prefer to fit this R14 hose which is a higher spec and will even cope with Methanol or E85. Gates R14 Stuart. Thanks Stuart - built in future proofing ! Quote Link to post Share on other sites
Rob Y Posted July 20, 2022 Report Share Posted July 20, 2022 On 7/17/2022 at 4:21 PM, Waldi said: Gates Barricade and Cohline have an ethanol-resistant grade (Cohline has several). Here is the Gates hose from Moss: https://www.moss-europe.co.uk/fuel-hose-gates-barricade-ethanol-proof-3-16-id-per-metre-gfh1018x.html Waldi I think I will go for this on the non pressure side hoses, so feed to pump from tank and return from mu and prv to tank. Can someone please confirm the ids of these hoses for me. Return lines are original but I have a Prestige fuel pump fitted with a bigger outlet fitting on the tank, do you know if this is the same id please? Moss website is down atm. Thanks Rob Quote Link to post Share on other sites
zelrik Posted July 23, 2022 Report Share Posted July 23, 2022 On 7/17/2022 at 4:33 PM, Waldi said: FWIW: The return flow from the MU is just a dribble on my car. The return flow from the PRV is much more. Waldi Does anyone know how big the flow of the MU return to the petrol tank should be? I temporarily drained the return MU flow pipe into a 1 Litre clear plastic container (while working on the M Unit) and it collected very much more than a "dribble" that Waldi describes. The MU return is described as "Leakage" in some workshop manuals - does this mean that petrol gets past a worn O Ring, or is there another way for petrol to get into the return-to-tank chamber? Quote Link to post Share on other sites
john.r.davies Posted July 23, 2022 Report Share Posted July 23, 2022 This diagram is from the Lucas Pi Manual, online version. As you can see, the return, 22, is labelled "Leakage fuel" fand collects what leaks fform the interface of the rotor and the body of the M/u. There's no O-ring. Quote Link to post Share on other sites
stuart Posted July 23, 2022 Report Share Posted July 23, 2022 4 hours ago, zelrik said: Does anyone know how big the flow of the MU return to the petrol tank should be? I temporarily drained the return MU flow pipe into a 1 Litre clear plastic container (while working on the M Unit) and it collected very much more than a "dribble" that Waldi describes. The MU return is described as "Leakage" in some workshop manuals - does this mean that petrol gets past a worn O Ring, or is there another way for petrol to get into the return-to-tank chamber? If that was without the engine running then yes you would get a fair flow obviously. Stuart. Quote Link to post Share on other sites
john.r.davies Posted July 23, 2022 Report Share Posted July 23, 2022 (edited) Zelrik, I had another look at my hard copy of the Pi Manual, and on page 24, under "Bench Testing", It says that on the test bench and at 1000rpm, "Fuel should be dripping from the leakage drain" No rate is mentioned, but "dripping" implies individual drops. A plumbing website estimates that one drop a second will pass five gallons (23 Litres) a day, which is about 1 Litre an hour. Drop size is a function of surface tension, so fuel may form smaller (or larger!) drops to influence this estimate, but either way, the flow is small! John Edited July 23, 2022 by john.r.davies Quote Link to post Share on other sites
zelrik Posted July 24, 2022 Report Share Posted July 24, 2022 Many thanks John & Stuart, that is exactly the information I needed - this Forum is a fantastic resource from knowledgeable people !!!!! The O Rings that I was asking about in my poorly worded question are the 2 surrounding the spinning MU rotor. One in the housing itself & one on the rotor. My suspicion is that if the O Rings wear &/or get eaten away, petrol pressure will build up in the "leakage" chamber that is too much for the small diameter return pipe to the tank. Could pressure build-up along the return pipe also be causing leaks in rubber hoses? The spinning rotor has a hole in the end (just visible in my picture below the scribe mark) does anyone know where it goes to or what it does? Regards Quote Link to post Share on other sites
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