Alright guys here's the scoop... 1990 xtra cab 3.slow about 265,xxx miles, oil pressure on start up is between the center lines like it should be. After driving for about 20 min it starts lowering to the point where the Guage is reading almost to the L on the Guage. Know it's not the rings cause she doesn't smoke, no noise of a dry motor... Thinking of changing out the oil pressure sending unit in the morning, if parts are available. What are other causes and how can I check with out being down for a long period as she's my daily?

 

I would get a $20 mechanical oil pressure gauge kit at the parts store and hook it up parallel to the stock gauge. See if its the gauge losing reading or the actual pressure. If you have a weak oil pump it will seem higher when it first starts until the oil warms and thins, then the pressure goes down. Might be able to run a thicker oil for a while to tighten it back up. 20-50 works nice in a 22R when the timing chain tensioner starts getting noisy. Don't think it would hurt anything in a 3.0. As for the stock sending unit, they are available but usually like 40 bucks. So I would check with a real gauge before I waste that money.

 

Can the screen in the oil pan get clogged? The one on the end of the oil pump hose? The assemble for the oil pump hose is like 100$ and a new pump is 200$

Don't want to spend money I don't have to, and I was thinking of seeing if I could rent a pressure gauge for the day. Hope it's not bearings... I can't afford that right now.

 

It could be a clogged screen but from the sound of it I don't know. Pull the pan down and check though, doesn't hurt to look.

 

My 96 Tacoma with the 2.7 did this. Was great til it heated up. Then it was nothing. It was the bearings and I replaced the engine. Excess journal wear does this.

 

^ yup as a motor racks up miles tolerances become looser decreasing oil pressure is the result
Some guys do little tricks like switching to the smallest oil filter they can find for there motors to pull some extra oil pressure ..be easy on the motor and it might be alright for some time

 

Talked to a couple machanic buddies and asked advice there as well. Here is a pic of oil pressure at idle after a 15 min drive to the parts store this morning:



Here is a pic at idle after a 20 min drive tonight:



What I did for now was an oil change and did a combination 60% 20-50w and 40% 10-30w. Didn't realize also that my last oil change I did was with 5-20w :/ I'm sure bearing races have wear and I'm sure ill have to do motor work at some point but I hope this buys me some time to be able to buy another motor an build that one before this one needs replacing...

 

Really ain't looking to bad I'm sure the gauge is a bit iffy on actual pressure readings depending on we're the sensor is located in the block . The journals will have a bit more pressure naturally . Could find a extra boss in the block should be one on the oil galleys hiding somewhere and thread an extra mechanical oil gauge with actual number readout for a bit more security and clarity

For instants my 350lt1 idles at 15 psi hot forty cold factory idle pressure specs are 4psi to 40psi is considered a acceptable range ..big gap in numbers

 

The thin oil you had probably added to the weak pressure. Sounds like you have it under control for now. Just baby it and keep the oil clean. You should have a few months to round up a new motor and get everything ready. Might be able to find a wrecked truck with a complete motor with lower miles for a cheaper option.

 

I'm using 0W-20 but i noticed when I was using 10W-30, the oil is thicker when not warmed up so there's more pressure, so it read a little higher.

I still get a reading with the 0W-20, but I know it's still flowing.

 

As long as there is ANY oil pressure at idle, you're fine. Toyota specs 3 psi at idle for all of their older engines that I've seen (80s-early 90s). As long as it's 1/3 up the gauge at 3k rpm, you're fine.

I use 5W20 in my 22RE and it still has 5 psi+ at idle and 50 at 2500 rpm after as long as you like pulling a trailer on the highway. Mine's a freak tho.

As a side note, you could leave hte rings out while assembling the engine and it won't affect oil pressure. Pressurized oil doesn't go anywhere near the rings.

another side note: thinner oil lowers all engine temps because of higher flow past parts. more oil passing by means more oil to carry away heat. There is a point of diminishing returns where the oil isn't adequately lubricating and friction causes an increase in heat but up to that point you're good. thinner oil also lubricates the parts farthest from the pump sooner because it flows more easily.

 

How to fix the oil pressure

The oil pressure problem is related to the pump and the bearings.
The way to fix the oil pressure is to remove the oil pan and pick up tube. Replace the pump and/or remove the oil pressure relief valve cup screw. Thing that holds the spring in place. place 5 to 6 stainless steel washers in the cup. This will increase the spring pressure. Screw the spring retainer(cup screw) back in to the pump housing. Remove the rod bearings and look for a wear pattern or signs of excessive wear patterns. If the bearings are ok then tighten everything back down replace everything and the oil pressure will go back up. WAY UP. You should shim the spring even in a new pump because these motors need more pressure the older the engine becomes. I know this because I have just finished rebuilding my 3.0 4x4 as a result of two bad oil pumps. So shim the spring and change the bearings and the oil pressure will be between 1/2 and 3/4. It works.