Where is my oil going?

Just as the title says, I’m trying to figure out where my oil is going. It’s a ‘97 3rz with 350k. Loses roughly 1 quart every 1k miles or so.

I know most likely culprit is that it’s burning it, but I have no indication of that. I have no cat on the truck and a straight through muffler, so there is nothing to prevent any oil smoke from making it out the tail pipe. Yet I have none. No visible smoke whatsoever. I pulled the plugs yesterday to see if there was any indication of burning oil on them. Nothing, all 4 plugs were a perfect light shade of cardboard brown. While I had the plugs out I threw a compression tester on there, and that was good with 145-155 psi across the board at 4500ft elevation. So all evidence indicates it’s not burning it.

as for leaks, the only thing I can see is a slight seepage at the oil pan. Just enough to make the seem look wet, but no running or dripping anywhere. Definitely not enough for the usage I’m seeing. When the oil usage started, I had a pretty serious leak at the oil pump cover that was bad enough to drip on the ground, but have since replaced the oil pump and cover and the leak is stopped yet the oil still disappears. The only place I’m seeing oil seepage that is fairly new is at the intake manifold junctions. Like manifold to head and where the two pieces of intake bolt together. They both have what appears to be fresh oil seepage, which would lead one to believe that somehow the intake is filling up with oil. As far as I can tell, both the vent line and pcv hose don’t appear to have had significant oil through them and the pcv valve appears to be clean and rattling. Just to be sure yesterday I through an inline fuel filter on the pcv hose just to see if it collects any oil. I don’t know how else oil would be getting into the intake, and I don’t know how if it is getting in there how it’s not visibly burning it at the rate I’m losing it.

sorry for the long post, anyone have any ideas?

Ohh yeah, truck still runs great and is still pulling 19 mpg with 35” tires.

 

How long have the current set of plugs been in the engine? A quart is pretty significant. What weight oil are you using?

 

I don’t recall exactly, but the plugs are a few years old. I know a quart is significant, that’s why it baffles me that there is no obvious sign of either leaking or burning. It’s either 5w or 10w-30 pennzoil ultra platinum. Had oil loss on supertech synthetic as well, but that’s when the oil pump started leaking so I just chocked it up to the leaky pump at that time. Probably a coincidence, but Honestly it all started about the time I had to switch to synthetic because conventional oil is getting harder and harder to find.

 

No oil coating under the truck from the transmission back?

Your checking the oil after the engine sits over night?

Coolant is still the correct color ?

It is leaking or burning . At 350,000 miles I would be happy with only using a quart every 1000 miles.

How many days to drive a 1000 miles a week or longer.

Good Luck

 

nope, truck is bone dry underneath

yes, checking after truck has sat all night

coolant looks perfect

10k miles ago it wasn’t hardly using any is why there’s concern. I know it’s leaking or burning it, it’s just that there’s no obvious sign of either.

it’s probably About 3 weeks to hit 1k miles and top her up. This is my off-road/commuter car.

 

I suspect that it is not a coincidence. How long have you been running the synthetic oil?

 

Im on the second oil change with it, so Probably the last 5k or so miles. I’m aware that it’s a possibility that the synthetic is causing some issues, although I’ve ran it on other high mileage vehicles in the past with no issues. It was shortly after switching to syn. that the oil pump started leaking so I fixed that and here we are. Also around the same time I regeared the diffs for bigger tires so my cruising rpm has gone up significantly from what it was with stock gearing so that may also be a factor.

 

Well, think I might have found the culprit. For whatever reason it appears to be sucking the oil out of the pcv. I put this filter in the pcv line yesterday for diagnostic reasons, and have probably put less than 50 miles on since. It has already accumulated what I would consider a significant amount of oil for that time frame. Now to figure out the cause, whether it’s just a significant amount of blow by or something in the pcv system not doing its job. Still weird that it’s not smoking.

 

You're burning it. There is oil blow by in the PCV system and that's why some people use catch-cans to catch that oil. With the miles you have on your engine, your piston rings are probably worn but it could be a valve stem seal issue as well. Regardless, your engine is consuming the oil.

 

I figured it had to be burning it just surprises me that at the rate of loss im seeing im not seeing any smoke with no cat and the plugs look perfect.

 

Simple way to check for bad blow by is open the oil cap while its running, if smoke or loud puffing comes out, there's excessive blowby.

It's expected after 25 years+ But really bad blow by shows up as smoke as you said.

 

its always blown oil splatters out of the filler cap if removed while running, even when I got it 8-9 years ago, so it’s hard to judge if it’s gotten any worse.

 

Car Care Nut can explain. The first vid is the one you want but the other two are interesting...

Edit: The first minute and a half he will explain normal rates of consumption for Toyota engines...


https://www.youtube.com/watch?v=v4JS7PybV2k

https://www.youtube.com/watch?v=YjsUsXc3TPU

https://www.youtube.com/watch?v=h6XnNAfQ904

 

A quart every 1200 miles sounds excessive to me for “normal” consumption. The rest of the video doesn’t seem to pertain to my issue. I’ve got no visible smoke, even with no cat. my compression is fine, it’s actually improved in one cylinder that was a bit low a year or so ago when I last tested it. Probably had stuck rings at the time that seems to have freed up. I also have changed the oil every 3-4K miles for the last 8-9 years. I’m sure the age and mileage is the main culprit, it just seems odd how quickly this issue has arisen and how there’s no obvious signs of oil burning other than the oil in the intake. I’m sure she’s on her last leg, but I’m gonna try whatever I can, might even have to try that fellas oil cleaning idea. Don’t have much to lose at this point.

 

You're not always going to see smoke. The pcv getting dirty quickly is a good indicator of blowby, as well as the pressure coming out the fill cap

Time for an engine rebuild or just keep topping it off