Guppy916 Posted June 14, 2021 Share Posted June 14, 2021 Should the fuel filter always be full to the brim when the engine is running ? I have noticed that mine sometimes has only 1/4" of fuel in the bottom, The fuel pump is new only a couple of weeks old along with the filter, Both were replaced when the old pump stopped working, for some reason the coil burnt out, and I noticed that the filter was only half full, a friend said that the pump was sucking air and over heated, the old filter was a glass unit that you can unscrew to clean out, so this time I opted for a plastic throw away unit, the tank is clean inside all fuel lines are new, and yes the filter is the correct way up, the pump runs at 5 psi to a regulator and down to 2.5 psi for the carbs, any idea's please Quote Link to comment Share on other sites More sharing options...
glang Posted June 14, 2021 Share Posted June 14, 2021 I think thats to do with the positioning of the filter as I have a very similar item but fitted in the engine bay just in front of the bulkhead with the inlet at the bottom. Any air is sucked out of the top by the mechanical pump so the filter remains full all the time. Not saying it cant run perfectly ok as youve got it though as I think if the filter blocks up at its base the fuel level will rise to compensate... Quote Link to comment Share on other sites More sharing options...
Rosbif Posted June 14, 2021 Share Posted June 14, 2021 My filter, which is fitted just before the pump, never has much petrol in it and the car runs very well. From what others have said/posted on the subject it is very common for the filter to only have a small amount in it. Quote Link to comment Share on other sites More sharing options...
glang Posted June 14, 2021 Share Posted June 14, 2021 Out of interest Rosbif does yours suck from the top or bottom of the filter? Quote Link to comment Share on other sites More sharing options...
Rosbif Posted June 14, 2021 Share Posted June 14, 2021 The petrol arrives at the bottom and leaves at the top. You can see just how little petrol is in the filter Quote Link to comment Share on other sites More sharing options...
glang Posted June 14, 2021 Share Posted June 14, 2021 That is strange and I can only think theres a tube inside that comes down from the outlet to below the fuel level otherwise more of the air would be sucked out! However again I think as the bottom of the filter element gets dirty the fuel level will rise automatically to compensate... Would be interesting to see what it does when the engine is running? Quote Link to comment Share on other sites More sharing options...
Rosbif Posted June 14, 2021 Share Posted June 14, 2021 The fuel entering the filter body does so to the outside of the paper element. The exit pipe does/should go to the bottom of the filter sucking up the filtered fuel on the inside of the element. The fact that the unfiltered fuel is on the outside of the element means you can see if/when the filter is dirty. If the unfiltered fuel went to the inside of the element you wouldn't see when it was dirty - all the muck would be on the inside of the filter. A filter, of this type, fitted the wrong way round would still work, there isn't a non-return valve. Yes I know it is disconcerting to see the filter virtually empty but it works Quote Link to comment Share on other sites More sharing options...
glang Posted June 14, 2021 Share Posted June 14, 2021 Yes I can see that but why have the internal pipe? If the exit hole was just in the end plate it would work just as well leaving the dirt on the outside of the paper element but all air would be pushed out as well. All I can think is that as the element get progressively blocked up the level of fuel gets higher so that when showing full it means the filter needs to be changed... Quote Link to comment Share on other sites More sharing options...
Rosbif Posted June 14, 2021 Share Posted June 14, 2021 Are you saying the entry at the top and exit at base? AllI can think of is that the petrol enters the engine bay low down and it makes more sense of the flow to do wait does. On the other hand one fitted by the tank it would be more logical Quote Link to comment Share on other sites More sharing options...
glang Posted June 14, 2021 Share Posted June 14, 2021 No, either way seems to work but I just cant understand why in at the bottom, out of the top still leaves the filter only half full of fuel😵 Quote Link to comment Share on other sites More sharing options...
RobPearce Posted June 14, 2021 Share Posted June 14, 2021 That's perfectly normal even if counter-intuitive. You'll find lots of people on the web insisting that if your filter's orientation is upright it will always be full but that's simply not true. The fuel "wicks" up the paper element and it will perfectly happily sit there with the inside of the element completely full but the outside near empty. It's to do with surface tension, which would have to be broken to draw the air through, which is harder than lifting the fuel past it. Quote Link to comment Share on other sites More sharing options...
Guppy916 Posted June 14, 2021 Author Share Posted June 14, 2021 I thought that with a pump that delivers fuel at this rate, it should keep the filter full Facet SILVER TOP Fast Road Solid State Cylindrical Pump Sealed, reliable solid state internals. 12 volt. Requires separate earth connection to pump body via fixing bolt. Less than 2 amp current drain. Will self prime up to 1 mtr lift. Footprint 140mm x 82mm x 85mm high (without unions). 2 bolt fixing at 65mm centres. Removable, washable internal nylon filter. Weight 760gm. Operating temperature range -60 to +43 deg C. Will pump from 5 psi to 6 psi. Flow rate 132 ltrs/hour (35 US gal/hr.) Union thread size 1/8" npt. There's no way the engine use's 132 ltrs an hour, I have also checked the filter on the sender unit, Rob am I just getting my knickers in a twist for no reason ? Quote Link to comment Share on other sites More sharing options...
glang Posted June 14, 2021 Share Posted June 14, 2021 5 minutes ago, RobPearce said: That's perfectly normal even if counter-intuitive. You'll find lots of people on the web insisting that if your filter's orientation is upright it will always be full but that's simply not true. The fuel "wicks" up the paper element and it will perfectly happily sit there with the inside of the element completely full but the outside near empty. It's to do with surface tension, which would have to be broken to draw the air through, which is harder than lifting the fuel past it. That makes sense. Mine, which is mounted fully vertical with inlet at the bottom, wasnt full to start with but a few months later is - I wonder if the paper element has punctured🤣 Quote Link to comment Share on other sites More sharing options...
Rosbif Posted June 14, 2021 Share Posted June 14, 2021 Probably all to do with capillary action and physics. You could always try disconnecting the exit, suck fuel in until full and quickly refit the pipe then see what happens. Quote Link to comment Share on other sites More sharing options...
Guppy916 Posted June 14, 2021 Author Share Posted June 14, 2021 I shall experiment in the morning, Glang I shall turn mine up the other way , inlet at the bottom Quote Link to comment Share on other sites More sharing options...
glang Posted June 14, 2021 Share Posted June 14, 2021 I think, for the reason Rob says, perhaps over time with the filter vertical the trapped air can percolate through the paper and out of the exit leaving the case full. However it could even be down to the individual filter manufacturer... Quote Link to comment Share on other sites More sharing options...
Rosbif Posted June 14, 2021 Share Posted June 14, 2021 1 hour ago, glang said: I think, for the reason Rob says, perhaps over time with the filter vertical the trapped air can percolate through the paper and out of the exit leaving the case full. However it could even be down to the individual filter manufacturer... If air was vented via the exit it would end up in the pipework leading to the carb, this would surely upset the running of the engine? Quote Link to comment Share on other sites More sharing options...
glang Posted June 14, 2021 Share Posted June 14, 2021 Well if the air pocket in the filter gradually passes through the paper element as Im suggesting it would then go into the carb float chambers little by little and be released from there via the overflow vents so it shouldnt have any effect on the running. However if it escapes all in one go then it might momentarily produce a low level in the float chamber and consequently a weak combustion mixture... Once the air pocket has escaped from the filter then it should remain full unless the fuel system is drained at some stage. Quote Link to comment Share on other sites More sharing options...
RobPearce Posted June 14, 2021 Share Posted June 14, 2021 33 minutes ago, Rosbif said: If air was vented via the exit it would end up in the pipework leading to the carb, this would surely upset the running of the engine? No, because (as glang says) the air just pumps through to the carb float chambers. The fuel system on a carb engine is not sealed, it has a vent to atmosphere at the float chamber, so it's completely happy with air in the fuel as long as it can pump enough through to let the air out. It would be different on a PI but then you wouldn't be using one of those plastic filters. Quote Link to comment Share on other sites More sharing options...
RobPearce Posted June 14, 2021 Share Posted June 14, 2021 2 hours ago, Guppy916 said: Rob am I just getting my knickers in a twist for no reason ? Probably 😀 Quote Link to comment Share on other sites More sharing options...
Kevin R Posted June 14, 2021 Share Posted June 14, 2021 I agree. I would imagine that these air pockets exist in all corners of our engines in the oil/fuel and cooling systems - it is just that we do not have a window as on a clear fuel filter to see them and/or worry about them.. An ideal system would have a steady gradient from the lowest inlet (without voids) up to the highest outlet that would naturally self bleed. Braking systems are narrow bore, better designed and have more bleeding points because air will destroy the operation of the system. However the circulation of a gas central heating system will still function if there is air in the radiators - it just becomes less efficient due to reduced heat output. Quote Link to comment Share on other sites More sharing options...
Rosbif Posted June 14, 2021 Share Posted June 14, 2021 55 minutes ago, glang said: Once the air pocket has escaped from the filter then it should remain full unless the fuel system is drained at some stage. How long do you think an air pocket would last? I changed mine a couple of years ago and as you can see nothing has happened yet. As I said it all works fine so I don't bother about it 1 Quote Link to comment Share on other sites More sharing options...
glang Posted June 15, 2021 Share Posted June 15, 2021 Hmmm difficult one as I wasnt monitoring the level but certainly around 6 months or so after having seen it half full it was then completely full. It had been run very little in that time but as you say if it works dont worry about it.... Quote Link to comment Share on other sites More sharing options...
Guppy916 Posted June 15, 2021 Author Share Posted June 15, 2021 Well after trying it every which way ! input at the top, output at the top, vertical or horizontal, 45 deg, it wont run full, if I start with it almost full a few mins on tick over and its half full, and there it stays ! so as Rob has said "nothing to worry about" thank you all for your views and advice Quote Link to comment Share on other sites More sharing options...
Dave Clasper Posted June 18, 2021 Share Posted June 18, 2021 Mine is similar orientation to Rosbif's, and always between a 1/4 to, on occasion 1/2 full, (though don't know what it like when driving?). Never a problem (it has on occasion stumbled on M Way inclines, when keeping the revs up), though this could be other causes I guess?. Dave Quote Link to comment Share on other sites More sharing options...
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