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External Oil Filter not circulating/Oil P. Light on and off with RPM


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Information that's all it's about... like racerx said.. just because the red light went out doesn't mean you have 50 or 60 psi of oil pressure... same with fuel... suppose to be 3.5 but how do you know..

Without a gauge your only guessing....

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Never ran fuel pressure gauge..had quiet a few ol skool cars. Running 32/36 weber on 510 and heard that if fuel pressure was too low or too high, you will know.

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I'll admit my 521 is my first datsun, and the first car with a carburator .. and without gauges i wouldn't be able to tell you one way or another how to tune it , if my fuel pressure was right or wrong.or if it was running rich or lean or anything else...

As a noob I probably went over kill on the gauge but they have all given me valuable information...

Even if they are installed temporarily as a systems check you can't go wrong...

Knowledge is power....

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  • 1 month later...

So I've been messing with everything for awhile, I installed a bunch of gauges and whatnot to get a better idea of whats going on and I've found I still have no oil pressure at idle. I've read it's supposed to be at like 10+ psi at idle but anywhere under 1200rpm I get little to no oil pressure and it starts getting rough. I've removed the dummy light sensor and put in a basic mechanical Bosch gauge and it shows everything is fine in the upper rpms. I put in a thicker oil to try and raise it which it did a little bit but not much, I was going to put my other oil pump on but I read that that's for volume not psi, so that might be an avoidable headache. What worries me is that from what I've read it might be a clogged pickup tube or something similarly annoying. 

I also noticed that when I shut off the engine and took the oil fill cap off there was some smoke so I'm thinking there might be any or very little oil getting to the camshaft which worried me.


Anyone have any clue to what my issue might be? if I have to take the oil pan off I might just swap the crank into my original L18 that I know is issue free so I can keep my manual trans, but I really don't want to do any of that if possible.


Other things I did were voltmeter gauge(not charging right), temp gauge, and installed an electric fuel pump that came with the car(inline fuse, relay, good grounds, switch, etc). The fuel pump i think helped to get my idle down to about 1000rpm without bogging so that was nice.

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First thing, get this back to stock oil filter location.


 What oil pressure???? Numbers. Every thing is fine means nothing. What does it read?


Take the valve cover off and start it up. If oil sprays everywhere then the top end in getting oil. Move onto next thing.



Go with the larger volume oil pump. Look at it this way...


Normally, at idle, the pump supplies moderately more oil than what bleeds out past the bearings and the excess volume backs up and begins to build pressure. About 20-25 PSI.


Rev it up, the rate of oil bleeding doesn't change so pressure builds till it reaches the relief valve setting on the oil ump. About 55/60 PSI



If you can't build pressure at idle it won't be a blockage on the pressure side but a bad leak, worn out bearings with lots of clearance, an oil jet broken off, a really worn out pump, Maybe the gasket between the timing cover and the block is leaking where the oil enters the block gallery on the way to the oil filter and just runs down into the oil pan.

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I always verify oil pressure with a separate mechanical gauge hooked directly to the engine and held in my hand. I have one specific for that purpose. I don't know if you've said what type of gauge you installed, is it electric or mechanical? It could be a bad ground (if using electric), or bad sender.


Your engine could simply be worn out. Excessive main bearing clearance can cause low oil pressure.


But I totally agree with Mike. You still need to do your due diligence and remove that remote filter and install a block mounted filter before you can come to any conclusions.

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Sorry it took me awhile to respond, I've been busy. I put a regular filter on as I said previously and my gauge is mechanical connected the old oil pressure sensor port. The pressure builds up normally when revved but it's very low around 1200 rpm( about 10 psi) and pretty much non-existent at 1000 and below and it starts to idle rough.

Before I put this engine in I replaced the timing chain and every gasket I could(head, oil pan, timing chain cover set, water pump, oil pump, etc) so the main bearing being worn out sounds like the most likely culprit due to the history of the engine.


I'll put the other oil pump on when i get the chance and see if that solves it, if not is worn out main bearing a cause for concern? I could tear out the engine again, I'd just rather not unless it's important and I've never touched anything on a crankshaft before besides the flywheel.

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Have you tried a different oil pump, I can't remember. The D-21 Hardbody pump is a high volume unit. This might move enough oil to give you some pressure at idle but in reality this is not fixing the underlying problem. Something is very wrong.


Might be the bearings are bad, but to have zero pressure the rods would be knocking I would think. With some effort if you can get the pan off with the engine in the car the mains and the rod bearings can be replaced without removing the crank. My very tired L20B still ran 17 PSI at hot idle.

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are the pictures showing that the inner hose on the block goes to the outer hose on the remote mount ?   That would be simply avoided by a correct filter or "shorter filter" that avoids a chance of doing a simple mistake. 

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 Was the oil pump ever replaced?????? If it wasn't this needs to be done to eliminate it as the cause. Easy enough to do. Any old pump will do just for proof.


If it was changed... for oil pressure to be this low the bearings would have to be so worn and with so much clearance, the engine would knock and rattle.

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