Pre-oiler plumbing question

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Feb 22, 2021
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I've read the posts here regarding pre-oiler plumbing, and the generally accepted way seems to be to take the input from the sump, and connect the pump output to a oil filter sandwich plate so you get filtration while running the pre-oil cycle. My question is, what prevents the oil being pumped into the sandwhich plate from just backfeeding through the engine-driven oil pump and back into the sump? Is it just a matter of there being slightly less resistance to flow through the filter-engine, rather than through the engine oil pump?

For anyone wondering, when I talk about a pre-oiler, I am referring to an electric oil pump that is cycled prior to engine startup to lubricate prior to cranking.
 
I would definitely not argue that it at all necessary, I just like building my vehicles way over the top. I'm mainly just asking as I'm interested in the mechanics of the system.
 
The manufacturer of the oiler probably has installation suggestions on their website if you haven't checked already. Don't most oil filters have one way check valves?
 
The oil flowing from the electric pump is plumbed into the input side of the filter, via a sandwich plate/adapter. The oil filter check valve has no effect, as the pumped oil is connected to the system prior to entering the filter. My question is just regarding the nature of an average engine's oil flow, and if there is anything that prevents oil from flowing back through the engine oil pump and into the sump. Is there some sort of check valve built into most gear engine oil pumps?
 
I have one on my 88 E-150 since I bought in new back in late 1987. It uses a special drain plug that is Octagon shaped, which has a copper nipple for the hose, and a drain plug which accepts a 1/4" Allen key. Oil is sucked from the bottom of the oil pan, runs through a filter and into a Tee off of the oil sending unit. I have it wired to a toggle switch. When I get into the van I flip the switch with the ignition key in the on position and watch the oil pressure gauge rise to the normal range, then start the engine. It can be set up with quick connectors and used to drain the oil as well. After long hot summer runs you can also turn the pump on after shutting the engine off and allow oil to flow to aid in cooling off the engine. I bought it because at the time the van would often sit for a month or more without being used. The pump I have was made for this purpose.

The pump also has a very fine screen in it to keep junk out. When I replaced the hoses, three times now since I have the pump on the van, there was not one spec of junk in that screen.
 
I have one on my 88 E-150 since I bought in new back in late 1987. It uses a special drain plug that is Octagon shaped, which has a copper nipple for the hose, and a drain plug which accepts a 1/4" Allen key. Oil is sucked from the bottom of the oil pan, runs through a filter and into a Tee off of the oil sending unit. I have it wired to a toggle switch. When I get into the van I flip the switch with the ignition key in the on position and watch the oil pressure gauge rise to the normal range, then start the engine. It can be set up with quick connectors and used to drain the oil as well. After long hot summer runs you can also turn the pump on after shutting the engine off and allow oil to flow to aid in cooling off the engine. I bought it because at the time the van would often sit for a month or more without being used. The pump I have was made for this purpose.

The pump also has a very fine screen in it to keep junk out. When I replaced the hoses, three times now since I have the pump on the van, there was not one spec of junk in that screen.
Thanks for the response, sounds like a good setup. My only concern would be pumping unfiltered oil from the sump straight into the engine via the pressure sending unit port. That's why I've read that folks generally use a sandwich adapter to tap into the system just prior to the oil filter.

Which takes me back to the question of whether oil can be forced "backwards" through a stationary gear-type oil pump on the engine...
 
Yes, gravity will cause oil to flow backwards and why filters have ADBV's

Use unfiltered oil and pump into an oil pressure sender port. The oil filter spends enough time in bypass so don't get hung up on the filtered oil. The other option is to use a small filter on the preluber.

So, what year/make/model/vehicle is this going in?
 
Yes, gravity will cause oil to flow backwards and why filters have ADBV's

Use unfiltered oil and pump into an oil pressure sender port. The oil filter spends enough time in bypass so don't get hung up on the filtered oil. The other option is to use a small filter on the preluber.

So, what year/make/model/vehicle is this going in?
This is correct. My pump has a serviceable screen filter built in which filters oil before it enters the pump. As I mentioned the few times I serviced the hoses that screen was spotless. I would imagine a 3/8" Magnefine transmission fluid filter could be plumbed in, which as Greasymechtech alluded to, is really not needed. It is however an option should you decide to go that route. I would also Imagine you could use a remote filter, or the sandwich adapter you mentioned. I decided not to complicate things, and was assured the way I had it was the best way to do it at the time. This pump has been in service since late 1987. In fact I have another pump sitting in a box I was going to use on a boat, but decided not to. Maybe one day I'll put it to use.
 
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