Low oil pressure light at idle

Hey, I'm new here but a long time admirer.
I have wanted to own a Tacoma as my first truck for a long time, and recently I was finally able to make that a reality. I purchased a 1997 Tacoma 2wd 3.4L V6 from its first and only owner a few months a go. It has 203k and was lovingly maintained, plus several brand new parts on the engine itself. New radiator + hose, all belts new, new head gasket, spark plugs, ignition coils, front and rear shocks, brand new AC system, etc. Too much to list.

Here's the problem: Truck runs and drives like a dream, I've had no complaints. However, recently I'm getting an intermittent low oil pressure light at idle. The light only comes on if the truck has been running for 20+ mins and the rpms fall at or below 500. So basically I have to be idling at a stop, or nearly at a stop for the light to flicker on. As soon as I so much as graze the accelerator, the light goes right off and remains off as long as the engine is under load.

Here's what I've tried: I replaced the oil pressure sensor (this made no difference). While I was doing that, I got an oil pressure gauge, let my truck warm up for awhile, and tested things out. What I found is that the oil pump itself seems to be doing its job, and the oil pressure easily achieves spec parameters. I couldn't get the low pressure light to come on while I was testing things out, probably didn't run it for long enough to replicate, I dunno. The lowest the pressure fell at idle was around 8PSI (I think toyota spec for this engine says 7PSI at idle and low pressure light at 5PSI?), but the minute it fell to 8PSI the pump would kick in a bit more and bump it back to 10PSI. It seems like good news because I do not think it's my oil pump but it is frustrating that I couldn't seem to replicate the problem enough to help my diagnosis.

Here's some ideas I have:
I'm wondering if this may be a sign I have a clog in my oil pickup screen, or even just a lot of sludge/crud in the oil pan itself. Is it worth dropping the pan, cleaning things up and poking around?
Alternatively, I'm worried this is a early and more sinister sign that my main engine bearings are getting worn...in that case, do I try a higher weight oil to try and bid my time as I save for a rebuild/engine swap? It had an oil change about 1k ago with 5W30.

I'm at a bit of a loss and feel defeated seeing as the truck is so new to me and was a dream of mine to own. I really value your guys' expertise and am eager to hear your thoughts.

 

if you keep RPMs above 550~ oil pressure stays in spec?

If so it sounds like everything is fine aside from the low idle

 

Correct. The low oil pressure light only comes on at idle, and only once the truck has been running for 20+ minutes. But if I'm idling in stop and go traffic, the light is of course consistently on, which seems like a potential problem for engine wear and tear reasons.

 

simple, throw a oil sender / switch at it,
if that doesnt fix it, throw an engine at it.....

 

Now that I read what you wrote, go throw an entire bottle of Lucas heavy duty engine oil stabilizer, its actually REALLY good stuff...
The entire bottle.....
Not going to hurt anything....

If it fixes it, your crank bearing clearances are wiped-out,
Needs a rebuild...
wont be an oil pump....

 

Maybe try a 5 minute oil flush and let drain overnight.

 

I would try and figure out why it is idling low enough for that oil pressure drop. it should be 550-650ish RPM when warmed up and keep you in the happy oil pressure range

opinions vary but I would focus on that and would avoid doing flushes or oil additives except as a last resort

 

If you think its sludge...
Couldnt hurt to try Valvoline Restore, heard good things about it....

 

Pickup screen is most likely.

Thicker oil or stabilizer will increase oil pressure sure but its not the answer.

 

As engine warms, oil thins along with crank bearing tolerances increase in-result drops oil pressure excessively low & triggers the light....
Could do this for another 200k if its normal wear & not due to lack of maint, sludge, etc....

 

I agree with @Wulf, < 600 rpm is a low idle (out of spec) and that's the primary issue that need be addressed.

My 5vz idles at 650-700 rpm, or 750-800 rpm if the AC is on.

 

Heres another scenario...
Be 100% certain you dont have ANY oil residue in the connection wiring from the previous oil sender leaking.
The oil can ground out the circuit on the side of the sender & cause light to come on...
Brake clean & lots of pressurized air from a compressor....

Ive seen that bite lots of rookies around me....

 

I also agree with others, about base idle needs to be 100% on point....
I dont know much about these engine but couldnt hurt to clean your throttle body plate, IAC valve & ports if it has one, etc.....

 

You did not mention the the engine you are referring to, but 500 RPM is lower then spec for:

5VZFE - 600-800 (warm) 1200-1800 (cold start)
3RZFE - 600-800 (warm)
2ERFE - 650-750 (warm) 1200-1500 (cold start)

I am not 100% sure on these numbers, so you should look them up in a manual. But assuming the above numbers are correct, running at 500 RPM would be significantly lower than recommended and would give you less oil pressure by nature of the engine just moving to slowly to build up the pressure.

There are a host of reasons that your idle could be off (e.g. Idle Air Control, dirty throttle body, mass airflow sensor, etc.) I am not a professional mechanic, so take what I say with a grain of salt!

 

First off i want to commend you, a girl working on a truck, very rare, very rare.

Plan A
For your piece of mind you can drop the oil pan and look at the pickup screen. It the pan has never been off before the FIPG, (form in place gasket) that Toyota uses is extremley difficult to break the seal, dont use a screwdriver to pry, use a putty knife and just keep working it between the pan and the block, others might have different methods, the point being is you do not want to distort the oil pan sealing lip. When the pan is off you can take off a rod cap and a main cap and look at the bearings. I forget if Toyota uses a babbit, cooper, steel bearing assembly, if they do and there is copper showing through the babbit and the bearing surfaces have no grooves then you have a decsion to make, try to slide new bearings in with the crank in the block or pull the motor and go through her. It is scarrier than it actually is. I have done both... this is a patch at best as the bearings for the camshaft are just as worn as the mains and rods and any excess clearances affects the oil pressure throuout the entire motor.

Plan B
Run 50wt oil

Plan C
Shut it off at stop lights.

 

Welcome to TW...

 

Thank you for the respect and the advice, it's much appreciated. I admit that plan B and plan C are looking pretty sweet right now. I'm hesitant to go to the trouble of a patch fix if the whole engine needs an overhaul. Based on what others are saying, it seems I have another problem of a low idle that may be contributing as well, so I need to figure that out.

 

I mentioned in my post that it's a 3.4L V6, so the 5VZFE. I appreciate the clue in about the low idle, I hadn't even thought about that being a low idle speed. I'll double check my manual for spec, but it definitely sounds like I'm idling low.

 

I would warn against plan B. Running heavy weight oil can cause other problems. There are tolerances all through the engine that are specifically designed with 5W30 in mind. Using thicker oil or additives can slow the flow of the oil in the engine in general causing problems down the line, especially in the top end of the engine. I would first work on getting your idle up to spec which should fix your issue without causing and issues down the line.

 

Sorry I missed that! I have the same engine, and my idle hovers around 700 +-.