LS swap lost oil pressure

[iamtherealJayy]

So I recently finally finished my ls swap and started driving it. Once I’d made it to the point of starting to let it run more I changed the oil(before it ever left the yard) the engine runs smooth and quiet without any crazy noises. I used an aluminum adapter piece by lanzar? Or something another and out my old oil pressure sensor in the back of intake. It did fine with around 30/35 oil pressure at idle and it increased with rpm(better than the old 350 with 10 at a 20° cold start with high idle) I’ve put roughly 100 miles on it so far and I’ve noticed the oil pressure lower and lower each time I drive it and arrive at my destination. (Roughly 5 mile drive) I averaged 20 but the temp sensor never got up to 200 or anywhere close straight up on the gauge(factory gauge from the k10 with an adapter in passenger side head) but yesterday when I was trying multiple combinations of mufflers and tips and angles etc I let the truck fully get up to temperature and I noticed the gauge showed <10psi oil pressure, shut the truck off took a picture and left it alone for the night. Temperature outside is roughly 80-85° I started the truck this morning and it started with around 20psi oil pressure but no noise at all still instantly shut it off and drove something else to work. I checked the oil and it is in the hash marks but it’s probably a half quart low. What could cause the oil pressure to get lower and lower each time I drove it? I really don’t want to replace this engine already, I haven’t even finished clutch break in so I’ve been easy on it. Oil still looks brand new smells fine, 5w30 green jug, Castrol or something? Same thing I’ve ran in my tbi for years without issue. Should I add a half quart of thicker oil and hope it helps? I’ve read about an oring but I don’t know anything about the internals of an ls this is my first one.

 

[Ricko1966]

Between the hash marks isn't over or low. Under the hash marks is low over the hash marks is high. I intentionally run my stuff just over the bottom mark,it has advantages. But if you are Between the hash marks the level isn't your problem. Adding 1/2 a quart of thicker isn't going to do anything. If you have 10 psi per 1000 rpm you're good. Put a mechanical gauge and a tach on it. See if you actually have a problem

 

[iamtherealJayy]

I’ve got a tach, I do not have a mechanical gauge. The tach is inaccurate it reads lower than it’s supposed to. Where’s the easiest place to connect a mechanical gauge? Either way when it’s fully up to temp I do have an issue. It does increase pressure with rpm but it’s maybe the bare minimum across the board

 

[R Carnella]

This might be a broken o ring seal on the oil pump pickup tube,very common.

 

[iamtherealJayy]

What all goes into replacing that? And anything else to look at while it’s apart?

 

[R Carnella]

You'll need to drop the oil pan and unbolt the oil pickup tube,then replace o ring.
There are two o ring styles (brown or green) match accordingly. Pretty easy job and gives you an opportunity to clean out all the crap that collects in the pan over time.

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[iamtherealJayy]

Is this something that can be done with engine in the truck? Truck is a 1978 k10.

 

[R Carnella]

Definitely yes. You should have plenty of clearance to remove the oil pan. And if need be (worst case scenario) unbolt motor mounts and raise the engine a little.

 

[iamtherealJayy]

Is there anything I need to watch out for that could happen while removing it? I’ve never touched an ls engine other than this one. $5 oring is way cheaper than 1200 for another 5.3 off marketplace.

 

[R Carnella]

Not really, it's pretty straight forward, nothing you can screw up. Remove oil pan perimeter bolts, drop the oil pan,unbolt pickup tube, replace the o ring seal, clean the crud from the bottom of the oil pan and reassemble. The oil pan gasket is reusable but i would pickup a new one anyway just to ensure no leaks. Use a very thin layer of ultra gray rtv on the oil pan gasket just as extra insurance it won't leak.
Should only take a couple hours.

 

[iamtherealJayy]

How do I know which color I need before disassembly? Engine should be an LM7? 99-02 Silverado/Tahoe 5.3L. I’m hoping the oring will fix my issue since it doesn’t have any engine noises or anything but the pressure is way lower than I’d like. Inside the valve covers looked amazing so I don’t think the engine is super high mileage but I don’t know any previous history on it.

 

[R Carnella]

Just get both before you start so your covered. There is a yearly breakdown of what engine got witch o ring but just get both. The O ring just gets old and breaks down regardless of miles.
Cheap and easy process worth doing in my opinion.
It can only help.
Cleaning the crud from the oil pan is kinda satisfying too...

 

[iamtherealJayy]

I’ll work on getting that done.

 

[iamtherealJayy]

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Here’s a cold start video with an outside temperature of around 66°, no engine noise but gauge shows 15ish psi cold. Whenever it stops raining long enough I’ll get into putting a mechanical gauge on it. What’s the best spot to hook the mechanical gauge? I don’t really want to fight with the factory sensor location it was hard enough getting the adapter and sbc sensor back there.

 

[Matt69olds]

Remove the oil filter, use some tin snips and cut it open. Look inside the filter media for debris. If the filter is clean, rest assured the engine is probably fine. Install a mechanical gauge to verify the engine actually has low oil pressure. If it’s in fact low, look into the o ring.

I’m not a LS guy and I’m aware of the Oring issue, it’s pretty common.