I installed a jdm 3.0 in my 94 4runner prior to install I replaced timing belt and all gaskets. Fired right up runs great not a problem. Drove around town no leaks not a drop. Finally get it on the freeway runs great when I stop a huge oil slick down a quart 5 mile trip. Thought maybe it will work itself out.... didnt. Cleaned it up real good same thing low speeds no leak ...freeway a mess. Can't locate source tear back into it replace gaskets galley plug that's what I thought it was.put back together......same thing local dealer looked at it said they couldn't find the source nut with 4 hours clean up an tech time they might be able to. Heck I'm perplexed any thoughts

 

So it's only at speed on the highway.....hole in oil filter? What about oil pressure sending unit?

 

Thanks for the reply. I've checked both the filter and sending unit. I wish that was the issue would have saved lots of grief from my son who wants to be driving this rig.

 

Had a Chevy that liked to blow its dipstick out due to blowby and spray oil everywhere on the highway. But then there was a lot of smoke from oil burning off exhaust manifold too. Check your oil cooler o-rings on the block (if equipped) and associated lines. Sounds like high crankcase pressure from higher RPMs are pushing oil out somewhere.

 

Crankcase ventilation is a good point. You gotta make sure when you reinstall the upper plenum that the PCV line isn't pinched. Otherwise, the already mentioned inspections are good places to start.

 

I would certainly go with the PCV or something related to the oil cooler located on driver's side of the block. Just a thought, could it be a cam seal since it is behind the T-Belt cover, or rear camshaft seal?

 

Just thought of something else so simple we sometimes overlook.... is the oil filter tight and the correct one?

 

so where is the oil once its low...drivers side passenger side...etc. I had a similar issue on a car and it was rear main was just old...replaced it and all good see if its dripping out of the bellhousing.

 

Clean it up, put it on jack stands, set the rpm's at 2000 and watch. Oil pressure increase over 2000 rpms are slight so you'll be spinning the engine at a simiulated freeway rpm. Obviously it is a pressure leak. Auto parts stores also sell a dye for engine oil. Flourescent green makes leaks easier to find. No blacklight needed.

 

Clean, clean, clean! You can't even see the leak now, what are you going to do when you get "close"? Gravity (and air flow) will blow that oil all over the place. You need to get the engine clean enough to eat from, so that when you first see the oil you can see right where it's coming from.

I've had good luck with spray engine degreaser and a garden hose; I'd lay off the pressure washer. You'll need a good place to work (a driveway with some slope). The local car wash won't work as well; by the time you get it to some place where you can look closely, everything will be covered.

Good luck!

 

Clean up the engine as has been suggested, put talcum powder/baby powder or any such fine powder on the engine, place engine on stands as suggested previously, run at higher rpms and look for fresh oil in the wet powder.

During freeway driving oil drips down and blows back on the engine.