Confused about oil pressure measurements

Just picked up a 2003 Tacoma 5vx-fe 4x4. 204k miles... engine sounds good to my untrained ear with the exception of what I think is power steering squealing for a while when I start up.

Few days ago the oil pressure light started flickering on off. I stopped car, listened and heard no concerning engine noises or knocks. Light went away after turning off and on but after more driving came back on.
I changed the oil pressure sending switch next day and did more driving After 30-45 mins of driving the oil light appeared again with new sensor but no engine noises or knocks. Would go away and stop/start of motor. I purchased an oil pressure tester from Harbor Freight to check things out. After connecting oil pressure gauge the pressure started high 50 PSI or more. As truck idled and warmed up it eventually got down to about 10 psi. Reving to 2-3k rpm I saw gauge rise to 25-35 psi.

I threaded the pressure gauge through the firewall and went for a drive to watch the pressure. Pressure slowly started to decrease from 10psi towards zero. Reving to 2-3k rpm didn't increase pressure. So now I'm really concerned.

I put truck in neutral, turned it off and coast a 30 secs or so and turn back on and oil pressure was 10psi at idle and raising to 25-30psi at 2-3k rpm. I drove for a while and it slowly lost pressure and repeated turning off motor and then back on and pressure would seem normal.

What might I be dealing with here? Bad motor? Strainer picking up sludge, trash? Bad oil pump? I'm far from a subject matter expert. Please help!

 

Just how does this Harbor fright gauge work electric or manual meaning you ran a oil line into the cab??

What weight oil is in the truck and when was it last changed ?? An omission that was not mentioned??

Old tired oil will tend to lose pressure as things warm up

As a old tired engine will as well then a neglected engine can be old and tired at 50,000 miles

 

Welcome to TacomaWorld

 

Manual gauge. Had a 1/8-28 BSPT x 1/8-27 NPT female adapter that screwed in snuggly. I popped a grommet out the firewall and fed the hose through for driving test. I think it confirmed what the lights were telling me.

I will be changing the oil today to a known weight to be certain. Will use 5w30 and new filter then repeat tests. Oil looked and smelled clean when purchased.

It agree about the old broke down oil but what is surprising is briefly stopping the engine and restarting restores pressure.

 

You did bleed the air out of the line??

air in the line can cause false readings might be why shutting off the engine boosts pressure for some time.

 

I did not do that or consider it. I don't believe there was mechanism to bleed of air. I'll see if I can manually bleed.

Given how the two sending units behaved when I briefly shutdown the motor I thought I was witnessing same behavior with manual gauge.

 

Scary situation you have there.
After seeing your test results I would be inclined to pull valve cover and check for sludge before pulling oil pan.
I've seen gunk and cleanish oil in the same engine.

 

Yeah... but I took the risk and will live with outcome.

I can see its not pretty through oil cap but not sure of magnitude.

Oil pan removal is preferable but a big job for someone with my lack of expertise. Almost entire front end has to come out. I know from experience I can cause myself 3 more problems trying to fix one.

 

Take an oil sample and have it tested, they will tell you if you have metals in the oil, like copper from bearings

 

I run a VDO oil pressure gauge on my truck at all times along with a Christmas list of other gauges. I like gauges, lol. It’s completely normal for the pressure to be higher when cold. My gauge pegs at 80psi on a cold start, averaging around 40psi on the road, and 20psi at idle when hot. My truck has 284k miles with 10w-30 conventional engine oil.

The first thing that comes to mind when I read your concern is sludge. One of two things is happening, either the pickup screen is plugged, and gets worse when driving, or my first thought there is sludge throughout the engine and your oil pump is pumping oil up into the engine faster than it can drain back to your oil pan. Either case, it’s not an easy fix.
The easiest way to find out if this is the problem is to remove a valve cover and check for sludge. If there is sludge everywhere you still have a few options other than rebuilding or replacing the engine.

First check the integrity of the rod bearings and crankshaft end play, removing sludge is only going to make a worn out engine knock louder. I’m assuming that you’ve already changed the oil and know that the engine doesn’t knock with regular oil in it. Oil stabilizers put in can hide worn bearings from knocking.


This is going to sound crazy, but it has worked well on low budget repairs throughout different manufacturers.
Remove both valve covers and the oil pan, clean everything as best as you can first with a vacuum cleaner, brake cleaner/acetone/paint thinner. Then move the vehicle to the yard and get prepared to make one hell of a mess. Spray purple power everywhere possible. Cylinder heads, and crank case area, you’re going to need at least a gallon. Pressure wash the inside of the engine, focusing on the oil drain back ports, and removing as much sludge as possible. Do the same underneath in the crankcase area. This works best with a steam pressure washer, and low pressure steam will actually make the engine internals look brand new.

Immediately move the vehicle back into the shop and use a spray bottle filled with wd-40, also available in a gallon container, and spray wd-40 throughout the engine while it’s still wet with water. Use your compressed air and a blow gun to remove water from the engine internals, while constantly spraying wd-40. This will prevent anything from rusting.

Finally replace the oil pickup tube and strainer, and assemble the engine. Fill with oil and a fresh filter and run to get everything up to normal operating temperature. Change the oil and filter once again.

Ive successfully done this on three different vehicles, never a Toyota, with good results. It is a lot of work, but it’s less work, and a lot less money than an overhaul....

 

Since suggesting an engine flush with kerosene would sound absolutely crazy I won't.
So don't run it with kerosene for oil, drain, change filter repeat.
Run it with oil light on till it seizes.
Am I clear?

 

I wish I had read this before typing out my solution to what the problem could be. Haha, I’ll bet my post blew your mind! I have a hard time sometimes because I assume most people work on their own vehicles, like I do. I’m also a technician for a living, and simple things to me, aren’t to others. My apologies.

 

Sounds like you have experience with straight 6 Chevy's.

 

They were all actually small block fords. One of the engines actually came out and was placed into an enclosed rotating hot water parts washer, in long block form. It was the worst to begin with but got it the cleanest in the end. Those Cuda hot water parts washers that noble oil services supplies are awesome!

 

i think I’d rather fill the engine with kerosene and run it for a few minutes to loosen up the sludge and then drain it out. That’s a trick my grandpa told me about when I was a kid. Never tried it myself

 

If your pressure was truly zero while the engine was idling you'd know.

Only a deaf person would miss it.

If the engine is viable but showing wear you can increase pressure by moving to the next higher grade oil... 20 to 30, 30 to 40, etc.

 

That’s not a crazy suggestion, as I have also heard of many people doing similar things to break the sludge down. Diesel fuel/transmission fluid mixture, kerosene, Marvel mystery oil, and even gasoline mixed with oil of some type. I’ve never personally done any of that though. The only problem I see with it is it will have to break it down quickly and not stop the strainer up and starve the engine of some type of lubrication.

 

The largest engine hot dip tank I've seen was in RR repair yard. Had to be at least 12' x 40'
After clean blocks were removed by gantry crane the cooled liquid was pumped out and sludge tonnage removed by excavator.
Can't help but wonder where that sludge was disposed of.

 

oil pressure is DIRECTLY related to engine load & RPMs

there is very little load at idle.............little oil need on bearing surfaces

the OP has a HIGH Mileage engine..............tolerances become bigger Reducing oil pressures

especially rod & Main beraings in bottom end

1st foremost i dont recommend stressing this engine further

NO run ups in rpms or 1/4 mile sprints

no doubt there ould be sludge + reluctant drain back of oil to the sump

an engine ‘ Flush ‘ by kerosene......detergents.......WD40 AL are Band Aide fixes

this engine is but a 1/2 step away from failure

id prepare for a swap or rebuild..................done before catastrophic failure

the death throws of ‘ Knocking ‘ is not always present



some of the notable solutions(??????) are merely every ‘ junk yard fix’ when

tryin to sell a questionable vehicle

how far will any of them net in mileage & NO issues in the future

short term fixes to get U out the driveway...................

another 40k or 55k miles down the road

if any bought a vehicle as such they would think theyd been duped

 

That's why I suggested valve cover removal to check if sludge had solidified and become crusty.
Best to remove cover(s) and pan to get crusty chunkies out, steam bleast, rinse repeat before solvent flushing.