Oil Pressure Drop at Idle

How much oil pressure drop is safe when idling for an engine at operating temperature? On my '08 Crewmax with 5.7L (193k miles), I see just under the halfway mark on the gauge when driving or when the engine is at or above around 1000 rpm.


If I sit at a normal idle with the engine up to temp for a minute or so, the pressure drops.


If I tap the throttle or take off from a stop, pressure goes right back up to normal and doesn't fluctuate. The weirdest thing is that the pressure drop doesn't happen consistently. While it always drops, it may stop halfway between the "driving" pressure and the "L" mark or it could go down to the reading in the second picture above.

I will likely have to dive into the engine to replace the timing chain tensioner(s) in the future but wanted to know if there was more I need to inspect. Or, worst case scenario save time by not working on this engine and buying a used one to replace it.

Any thoughts/opinions are appreciated.

 

It is normal for oil pressure to fluctuate, be lower at idle when warm and raise with RPM. If you are concerned you could plug in an actual oil pressure gauge that gives a number reading, as the factory gauge does not show actual pressure. I would think that if the engine sounds ok, no metallic clacking or excessive noise, you are good. But it is normal for the factory gauge to fluctuate up to about 1/2 the dial, depending on RPM and if the engine is work or a cold start.

 

How's the oil level? And frichco228 is right, the OEM gauge is a glorified on/off switch from a diagnostics perspective. We have no idea if the gauge moving from mid to low translates to 5psi fluctuation or 20psi.

There's a thread on this forum about OBDII scanners using OBDFusion and its Toyota specific diag pack, that could be useful to getting a real oil pressure number for you. Though I can't remember if these trucks have oil pressure sensors stock.

 

My Tundra consumed almost all of it's oil, all but one quart, and the oil pressure gauge never dropped from it's normal operating range. Also there was no low oil warning light or alarm.

 

That ain’t normal. Im about the same milesge as you. When hot (115* temps in traffic)...I’ve never seen mine sway much from square in the middle. Maybe a dash or two towards L.

Like was mentioned, I’d verify with a functioning gauge. Its possible(probably likely) the oil pressure sending unit is peetering out.

Keep an eye on it...dont take long to trash a motor running low oil pressure if the gauge is right.

 

Oil level is full. I understand some movement is normal but I honestly don't remember the oil pressure gauge always acting like this. There hasn't been any major event since I've owned the truck that I can think would have caused any damage (other than needing to replace the timing chain tensioner).

I picked up a replacement sending unit and was going to change it out quick when I do my next oil change (hopefully this weekend) and see if that changes anything.

 

Definitely something is sideways with the sending unit... or related... I'm at 230k 5.7 and have never dropped that low at any temperature, only when its off... but lately it's been slow to climb to just over half and coming back down like your 1st pic.

 

My 2007 with 265k sits just below half when fully warmed up & idling.

 

Specs for: Toyota 3UR-FE is a 5.7 L (5,663 cc, 345.6 cu·in)
Idle speed: 70 kPa (0.7 kgf/cm2, 10.1 psi) or more
2,500 rpm: 220 kPa (2.2 kgf/cm2, 32 psi) or more

 

I had an older Toyota pickup that was like that. It looked like the rod bearings were slightly worn. Back then you either got an idiot light or the nice set of gauges with a tach and oil gauge. Lots of people would go to the junk yard and find the gauge cluster out of an SR5 and put it in only to find the oil gauge wouldn't work. You also had to swap out the sensor as the idiot light was just a switch while the gauge was an actual pressure sensor. Yes the mileage wasn't correct but usually close and when you're using the truck to play in the mud you really didn't care about mileage. I think I ended up using a heavier weight oil.

Of course back then getting to the oil pressure sensor was much easier (being a 4 banger). It was also pretty easy to install an aftermarket gauge. You could see if TechStream will give you a real number (I would think it would) but my guess is either the sensor is reading wrong (probably not) or the oil pressure is actually dropping. Either way reading what the CPU is seeing will just show the gauge in the dash is working (most likely). So I would most likely try to find a place to add an aftermarket gauge to see what the pressure really is. Or just do an oil change and go with thicker oil. With almost 200k on it you might have worn rod or main bearings or cam shafts. Either way that's a full rebuild so going the thicker oil route really doesn't hurt.

 

Be careful on what you call thicker oil . On newer engines it can mess with some sensors, and give you engine lights. With newer synthetics , the old theory of thicker is better , ain't right anymore. Just run a good quality high mileage synthetic, and a good quality filter , maybe a Lucas or Mystery , additive would do you better at higher mileage. I've found in past even a different filter can cause a change in pressure. As far as bearing wear , unless you are extremely heavy footed, I wouldn't worry to much , These motors are built so much better , and closer tolerances , and at 193,000 it's normal wear , and my gages at 83,000 , read same as yours , and have from day I bought it with 34,000 .

 

Minor update: Did an oil & filter change today and replaced the oil pressure sending unit today. I'm not sure if it was the fresh oil or the sending unit but my oil pressure seems to have stabilized for now. I'll wait until I get a couple thousand miles on this oil change before I can say that it's fixed (the pressure stabilized with the last oil change also) but I feel a little better for now.

 

Glad to hear it worked out, keep us updated.

 

probably sending unit that was the issue.