I have not had the mechanical lift pump apart so I don't know that the guts look like.

What are odds of the mechanical lift pump seal failing failing and allowing fuel into the oil?

The reason I ask is not so much concerning diesel, however, the way some have their WVO piped the mechanical lift pump handles the WVO. If WVO got in the engine oil it would be a bad day if you didn't catch it quickly.

If your Fuel Supply/Lift Pump is the same as the 300D ones on the MW Fuel Injection Pumps there is only 1 O-ring Seal on the whole Lift Pump.
When that O-ring goes bad it is more normal for the Fuel to come out of the Lift Pump and mix with the Engine Oil.
However, 2 members have said a bad O-ring there sucked Oil out of the Fuel Injection Pump and mixed the Oil with the Fuel that was burned up in the Engine; there symptom was their Oil was disappearing but they had no Oil leaks and there Fuel was turning blackish from the Oil.

In this thread you can see part of the Lift Pump Taken apart (Post #9) and there is a tiny O-ring. The size of the ring is given in the thread (Posts #11 and #14).

Lift Pump Rebuild....

However, this is just a regular O-ring. It is not a Viton O-ring.
However, you might want to post in the biofuel section of the forum and see if a regular O-ring in the Lift Pump causes a problem with other Fuels.

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the info! Sorry I took so long to reply. I'm used to getting an e-mail on most forums when someone responds to my post. I posted a picture of the IP with the lift pump on the side. Is that the same lift pump?

Attached Thumbnails

 

Welcome to the forum John.
That lift pump looks like the one that has the O ring.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Hello John,

My 190D lift pump has so far seen 4000l of WVO passing through without problems.
I have a 2 tank system installed in the car and the stock lift pump is exclussively used for the WVO because it is so powerful.
For the start up fuel I have fitted a little Facet pump.

These cars are just perfect for veggie oil.

Kind regards
gonzalo

Thanks a lot for the information guys. I will be putting a 2 tank in as soon as I smooth out the nailing. I have Monark injector nozzles on the way!

That Lift Pump is not the same as the one on my 84 300D. However, it still has the tiny O-ring.
See the pic on the Thread at the bottom; the arrow on the Far right points to the tiny O-ring.
Where the other arrows point there may or may not be O-rings. I have never had the type you have apart.
Notice it has Disc type Valves; that work like the ones in the Vacuum Pump do.
95 E300D (606.910) Fuel Lift Pump Rebuild Question

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84 300D, 82 Volvo 244Gl Diesel

Diesel911, that is a nice post. It shows the O-Rings that I was asking about. Thanks.

Actually its not a lift pump as used in carbureated engines. Its as pressure pump that supplies fuel pressure sufficient to open the pressure relief valve in the IP.

P E H