Matt Harwood Posted August 26, 2019 Share Posted August 26, 2019 (edited) Just got back from a long with the Limited. About 750 miles, most of which were above 50 MPH. Car ran great with no issues, which made me very pleased. During the tour, I twice stopped to adjust the timing a bit to see if I could cure some light-throttle surging and both times I saw that the bottom section of my fuel pump was wet. I cleaned it off with brake cleaner but the next time I looked, it was wet again. Cleaned it and again tonight, after I got home, it's wet again. Where is the oil coming from? It is definitely NOT gasoline. It does not drip from that spot, there are no droplets on the ground under the fuel pump. The lines to the oil filter and the oil filter lid are tight. The fittings for the oil lines feeding the rocker arm assembly above the fuel pump are tight and dry. The fittings feeding the other lines and oil pressure gauge are tight and dry. There is some oil on the side of the block and on the oil pan lip, which also re-forms after I clean it up. So it's coming from somewhere in that area. I tightened the mounting bolts thinking that maybe the gasket between the pump and block was leaking. That may be it, but it's not obvious. A new gasket is easy. My only other thought is that somehow the vacuum pump part of the fuel pump is sucking oil and it's seeping out past the diaphragm. But if it's doing that, how is it getting on top of the pump? Blown by the fan? It's not sprayed all over the place, just wet on top. Check it out: Any thoughts? This seems really odd. Thanks! Edited August 27, 2019 by Matt Harwood (see edit history) Link to comment Share on other sites More sharing options...
edinmass Posted August 26, 2019 Share Posted August 26, 2019 Blow by from the engine coming out the Diaphragm vent. You probably can’t see it while the pump is installed. Link to comment Share on other sites More sharing options...
DonMicheletti Posted August 27, 2019 Share Posted August 27, 2019 There are seals on the diaphragm operating shafts (rods), Maybe one has reached the end of the road, Can you see the vent hole using a mirror? Link to comment Share on other sites More sharing options...
MCHinson Posted August 27, 2019 Share Posted August 27, 2019 I had a similar problem on my 1937 Century on long trips. I have now fixed the problem once and for all by installing a different rebuilt pump as well as switching to Grade 8 bolts to secure it to the block with new lockwashers. The original lockwashers had been weakened over the years and long high speed drives resulted in the fuel pump bolts loosening. Between that and a partially stripped small screw hole on one of the screws around the outside of the pump, the old pump would leak a bit of oil on long high speed drives that were not visible in regular day to day drives. Link to comment Share on other sites More sharing options...
Matt Harwood Posted August 27, 2019 Author Share Posted August 27, 2019 Thanks, guys. I'll add a new fuel pump to my fuel system rebuild this winter and keep this one as a spare. I'm relieved it's not something serious. Thanks for the quick answers! Link to comment Share on other sites More sharing options...
neil morse Posted August 27, 2019 Share Posted August 27, 2019 9 hours ago, Matt Harwood said: I tightened the mounting bolts thinking that maybe the gasket between the pump and block was leaking. That may be it, but it's not obvious. A new gasket is easy. Did it still leak even after you tightened the bolts? I had the same problem, and it turned out to be loose mounting bolts, similar to what Matthew describes. Link to comment Share on other sites More sharing options...
Marty Roth Posted August 27, 2019 Share Posted August 27, 2019 You appear to have a Dual-Diaphragm fuel pump, one for fuel, and the other to boost vacuum for the wipers, etc. I have seen a marginally defective diaphragm or gasket allow oil from the vacuum side which then migrates past either the weep-hole in the housing, or through a marginal gasket on the pump mounting surface. Link to comment Share on other sites More sharing options...
Pete Phillips Posted August 27, 2019 Share Posted August 27, 2019 On my '49 Super, I get a little oil on top of the fuel pump because oil leaks from the engine's side cover gasket. Pete Phillips, BCA #7338 Leonard, TX Link to comment Share on other sites More sharing options...
Matt Harwood Posted August 27, 2019 Author Share Posted August 27, 2019 I think the diagnosis of blow-by coming out the diaphragm vent is the correct one. I stuck my finger under it and there's a drop of oil hanging off what I believe to be the vent. That would make sense, since it's not blown all over the engine bay and isn't leaking down from the side of the engine. The weekend of high speed, long distance driving undoubtedly made it leak more than usual, which is why I only just noticed it. I've been meaning to get a spare fuel pump anyway, so I'll just buy a new one and keep this one in the travel box for back-up. The entire fuel system is going to be replaced this winter anyway so I can make it a few more months on this one before I take it all apart. This car isn't much of a leaker, so when I spot oil, it tends to stand out. It'll be good to cure another leak at least. Thanks for the great advice, guys! 1 Link to comment Share on other sites More sharing options...
FLYER15015 Posted August 27, 2019 Share Posted August 27, 2019 Matt, While you are in there check the timing cover bolts. I had a leak where the front plate contacts the block right down by the fuel pump, and the fan blew it back on the pump and along the bottom edge of the block Should be easy to check for when you have the pump out. Mike in Colorado 1 Link to comment Share on other sites More sharing options...
Rod Frazier Posted August 28, 2019 Share Posted August 28, 2019 I've found that the mounting bolts on my '40 Century loosen up periodically and require a good retightening. Link to comment Share on other sites More sharing options...
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