Low RPM + Oil Light

So cold today, in the teens with wind chills lower. I noticed when I came to a stop, the oil light would come on. It appears than when stopped in gear, my RPM's would drop to about 500 (hard to tell, halfway between 0 and 1k). If I put it in nuetral the RPM's would go up and oil light go off.

My only thought is the extra trans cooler is overcooling the trans fluid? When I get home tonight Ill check fluid levels but Im pretty sure its not low. Been driving it all week with no issues, just happened today.

 

What weight oil are you using?

 

Why do you think this would affect the oil pressure light???

The oil pressure light is activated off low pressure, not volume. If the oil is so low that the pressure drops (pan pickup is exposed) you have real problems.

What wt oil are you running? Dino or syn? Is the truck up to full operating temperature when this is occurring?

 

Increased viscosity of the trans fluid causing the engine to bog down when in gear? In neutral, engine RPM's go back up to about normal (600-800 RPM's).

Oil pump runs off the engine, I think. If the engine RPM's are too low, can the oil pressure drop?

5w-30 Pennzoil Pure Plus Technology Platinum Ultra Extreme Plus (whatever; the highest end Pennzoil Synthetic - I can't quite make sense of their naming scheme). Yes, the engine was warm. Didn't notice it when it was cold, turned on after I got off the highway and hit my first light.

 

Nah. Eliminated because you say the vehicle is up to operating temp. Granted for some reason the engine isn't responding well to that load, but it's not because of trans fluid viscosity.

Yes it does. Possible, but it doesn't take much to have the pump work. The pressure is measured by the oil filter anyway. I've seen pressure drop when the filter goes into bypass mode..........

Great oil. Shouldn't be the issue. I'm assuming you don't have a CEL lit. But if you have a reader you might check for pending codes.

Of course checking your fluid levels is always prudent.

Let us know what you find.

 

You dont think the extra trans cooler and all the highway driving (lock up clutch engaged), would over cool the trans fluid? The oil pressure light only comes on when the engine RPM's dip down and they only dip down with the gears engaged (Park and neutral make the RPM's go back up and light go off). Maybe something is causing idle to be too low

Ill keep and eye on it and check fluid levels this afternoon. I need a trans temp sensor...

No engine lights, Ill check pending codes.

 

Even wit h 500 RPMS light should not come on. If it does it means Oil pump is not giving enough pressure for pressure switch.
That does not mean oil pump is bad, it could be oil switch, it could be oil filter having pressure valve stuck in open position, it could be bypass valve stuck open. It could be multitude of things
Before anything I would check oil pressure at idle.

 

500 is a geustimate. I need to hook up my computer to get exact RPM, but its right in the middle of 1k and 0. Generally its on the higher end, towards 1k (around 6-700ish).

Oil pressure at idle in gear (500ish RPM's) = Too low (light on)

Oil pressure at idle out of gear (N or P) (6-700ish RPM's) = Ok (light off)

 

You should not be getting oil light at 500RPMS.
You RPMS are not an issue, in fact minium oil pressure you should be able to get as soon as Engine fires (little faster than starter RPMS)

So I would not focus on RPMS but rather why light comes on.
Its either due to low pressure or faulty pressure switch
if Its pressure switch that is a simple fix
but if you are not getting minimum at 500RPMS than you need to find out exactly whats going on.

 

Light is comming on when RPM's drop below a certain point. It will start to flash as the RPM's begin to drop (when coming to a hault) and stay there until RPM's go back up.

So what else is happening when the truck comes to a stop? What else is happening an parallel if the RPM's are not the issue?

The only variable that changed this week was the temp, wind chill was sub zero this morning and temps in the teens. Only variable that changed between this winter and last winter was the trans cooler

Should I not drive it if the light comes on everytime I stop?

 

As soon as I see a warmed engine oil light pop on at any time during driving, I pull over and check asap. It's the original idiot light for a reason. I was an idiot and ignored the thing once,,that's all it took.

You made it home without exploding a engine it seems, so I would venture a guess that you did in fact have good pressure. You would have heard the thing make evil sounds as you ALMOST made the driveway home,,or another mile or two or three down the road after the light came on.

BlueT nailed the high points on it.

Not the first time super cold temps affected a high mileage switch. It's a pretty easy cheap switch, and while you are there you can adapt a pressure gauge to the fitting area to check running pressure. Build a T fitting setup for a in-cab gauge and your pressure switch, if you so choose.

 

Ill check the switch. Light only comes on when truck is stopped and goes off quickly as I start going again. I put the truck in N when stopped to keep the light off so Im not too worried but def was a bit rattled when it first came on.

 

Additionally while trouble shooting, keep in mind the minimum oil pressure (v6) at operating temp and idle speed of 700rpm +50 is a scant 4.3 psi so your working with a pretty small range.

 

Start with cleaning your mass airflow sensor.

 

That 'may' have some idle down function, and won't hurt anything regardless. Nor will cleaning the throttle body.

But neither will correct whatever is happening with the oil pressure light, other than 'hide it' if the idle picks up again.

Oil pressure should be in spec as long as the engine actually runs.

 

Have you ever cleaned your throttle body?

 

Im with you on the switch. I check my MAF every time I change my oil an clean as necessary. I JUST installed a brand new OEM MAF.

A while ago. Wasn't that dirty

Toyota.

 

Did you check your oil?



If it was low, add oil.

If it was low, has it been burning oil? If so, how many miles do you get to a quart?

Has it been leaking oil?

If it wasn't low, its likely a sensor. It has nothing to do with your MAF or your transmission, or anything else, just your motor.

The light comes on due to low oil pressure caused by low oil (down more than a quart is what it would take to turn on the oil light) or by a faulty sensor.

So, first thing, did you check your oil?

 

4.3 psi is basically a steady pour out of a pitcher(or less). Crazy light duty pressure switch if so. Definitely verify your operating temp idle rpms as stated above as you diagnose.

 

Check oil pressure first. Harbor freight has a kit that has toyota adapter for cheap. Take it from there.
Do you have FSM ? There should be exact numbers that pressure needs to be at idle and high rpms. Before you check pressure everything else is speculation.