Oil leak from mechanical pump weep hole

Engine, Transmission and related drivetrain.
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PMCS Rally
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Oil leak from mechanical pump weep hole

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I have been test driving mine with stock L18 (with Weber 32/36) past 4 moths. Last week when I was back from 5-minute drive I noticed that substantial amount of engine oil was all over in passenger side engine bay all the way to the bulk head. I checked and the oil was from "weep hole" (for a diaphragm to breath??) of mechanical fuel pump. The pump was original and a half century old, so I replaced it with a new one. But I have the same problem with the new one. I do not see any abnormal pressure inside the cam cover or crank case. I have not done any modification to the engine.... just adjusting carb and timing right now. Any suggestion or advice would be greatly appreciated.

Thank you.
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datzenmike
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Re: Oil leak from mechanical pump weep hole

Post by datzenmike »

Could be the plastic spacer is cracked.

I don't think there is a weeping hole but the pivot pin opening could be mistaken for one. The pivot pin for the pump arm has leaked on me in the past on my 620. It was just an annoying dampness more than a leak. What I did was thoroughly de-grease with brake or carb cleaner and rub a dab of RTV on it to seal. It's not under any pressure. Just fumes and a small amount of lubricating splash oiling.

I never throw away parts. There's probably nothing wrong with your old mechanical pump. (that can't easily be fixed)
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Re: Oil leak from mechanical pump weep hole

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When this first started, I also suspected plastic insulator and gaskets failure. I removed the original pump and inspected all those parts and nothing found there. I cleaned up and replaced gaskets and reinstalled the original pump but it was obvious that oil was coming from a weep hole goes straight to diaphragm chamber of the pump. Then I installed a new pump but it did exactly the same. Considering the amount of oil spilled in 5 minutes, I am suspecting something other than pump itself. It makes me feel like I need add oil catch tank for this....Yes, I always keep the original parts no matter how bad they look.
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Re: Oil leak from mechanical pump weep hole

Post by datzenmike »

I looked for that and couldn't find it. OK they do exist.

Are you, by any chance, using a synthetic engine oil? I tried it once many years ago and oil began dripping from the front seal. Next oil change I went back to dinosaur oil and within a month it was gone. It's just too slippery for older engines. BTW I use Rotella T4 in 10w30. It's high in ZDDP and perfect for protecting out 'flat tappet' cams and rocker arms.
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Re: Oil leak from mechanical pump weep hole

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Characteristic of the oil was another thing I suspected. I never used synthetic on 510 and right now it's filled with conventional Quaker State 10W30.

If some mechanical pumps on L4 engine do not have this weep hole, maybe I can tap the hole and close it with a bolt. Looking at the structure of diaphragm chamber (I disassembled the original one) I do not think there is any affect of oil on performance of diaphragm.

Then maybe I need to worry about oil seepage from the pivot😊?? I saw epoxy material on pivot of some Z-cars. Back then I was wondering why.
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Re: Oil leak from mechanical pump weep hole

Post by datzenmike »

Quaker State is a low ZDDP conventional oil. They are formulated for today's roller cams that don't need as much protection. ZDDP is bad for the cats in them too. I don't trust them to provide protection for my cam and rockers.

A smear of TRV will seal it.
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Re: Oil leak from mechanical pump weep hole

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Thanks for the info. My knowledge of engine oils is very limited and I picked QS simply because it says " Protection for new and old engines. All Mileage" May be they did not mean a half century old😄. Which engine oil would you recommend for stock L series engines? I will try TRV.
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Re: Oil leak from mechanical pump weep hole

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Newer cars have different valve train and don't need the extra anti scuff ZDDP protection so makers have been slowly fazing it out as it damages the new catalytic converters. Oil companies say it's reverse compatible and the old levels were way too high to begin with. I'm choosing to not believe them because if wrong my irreplaceable cam and rockers are toast. It's just easier to switch to an oil that still has the old levels and that's diesel oils. I'm using Shell Rotella T4 10w30 but have used 14w40. Chevron Delo 400 is similar and Esso also makes one. Over the counter ask for a 'flat tappet cam' oil and they'll now what you mean.
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Re: Oil leak from mechanical pump weep hole

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Thank you for the information of the oil. I will switch it next weekend.
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