Let me preface this by saying I know very little about engines. I've done a ton of work on my 4Runner in the past 7 months but it's been mostly suspension and brake work.

I'm trying to track down the cause of a small oil leak. It accumulates on the skid plate as well as at the oil drain plug (lowest point I presume). Oil plug is tight with fresh gasket. I've added maybe 1/4 quart in 2500 miles, just to get the level to the top of full on the stick.

I added some dye recently but then it rained for days. When I finally got under to take a look, the dyed oil had sprayed everywhere. I wiped everything clean after the rain stopped and the next day noticed dyed oil on the left side and bottom of the oil pan, having come from somewhere above. There was also dyed oil along the bottom of the steering rack. Most notable to me though was a pooling of dyed oil in the highlighted spot in this image:



In April of this year I hired someone to replace my TB, WP, TS and VC gaskets. That's where this picture is from. It's also why I decided to learn to work on this 4Runner myself.

I should have checked long ago but I took a torque wrench to the 4 outer bolts on each valve cover yesterday and they all took multiple turns to get to 53 in/lbs. I was thinking that might be the source of the leak and I'd just need to learn what to remove to get to the other 8 bolts. In the image above it looks like it was a problem even before that work was done. I had no leaks for a couple months after the work in April. I drive maybe 250 miles/month. Currently just over 250k. I don't know if any of that is relevant.

Wish I had current pictures but here's a tighter shot:



Any suggestions as to where to focus my research on this? Is it something obvious? Maybe crank seal? Again, I know very little about engines but I'm keen to learn. I have the technology. I can make her better than she was. Better, stronger, faster. ( everyone here has a little Oscar Goldman in them, no? )

FWIW, I have a recurrent film of oil in the same exact spot. Not nearly as much oil as on your truck, but same location. I can't stand greasy motors, and try to fix every source of leakage that I see. I've replaced the valve cover gaskets, as well as the crank seal when I did the timing belt. And I can see that there is no seepage from either of those, yet the oil at that location keeps coming back. I replaced the dipstick o-ring (you might want to check that on yours), to no avail.

I was all set to replace all the hoses and o-rings for the oil cooler, but when I looked closely, there was not a hint of oil leakage from there.

So I"m at a loss too. The only thing I can possibly think of is perhaps a bit of oil spilling during the oil changes (oil filter is in that area), and eventually making its way to that area above the oil pan.

I'll be keeping an eye on your thread to see if you find your source.

I kinda doubt this would throw that much oil all over the place but you might check your dipstick seal. That picture above looks like its coming from there. When I did my valve cover gasket job the seal on it was pretty bad and had some oil around it. Its fairly easy to fix tho, so it shouldn’t take much to knock that off your list.

Just get some of the Toyota FIPG sealant, unbolt the bracket holding the dipstick guide to the engine, pull it, add some FIPG to the end of the guide where it mates with the pan, reinsert and install, and let sit for a bit. Make sure you clean around/on the dipstick so no grime gets into the pan.

In April of this year I hired someone to replace my TB, WP, TS and VC gaskets. That's where this picture is from. It's also why I decided to learn to work on this 4Runner myself.
Any suggestions as to where to focus my research on this? Is it something obvious? Maybe crank seal? Again, I know very little about engines but I'm keen to learn. I have the technology. I can make her better than she was. Better, stronger, faster. ( everyone here has a little Oscar Goldman in them, no? )

In your picture there is no crank seal installed, so it must have been replaced with the timing belt. Maybe it wasn't installed right. Could also be dipstick tube seal, oil filter, oil cooler, oil pan gasket, oil pressure switch, cam seals or cam end plugs. The valve cover gaskets are the number 1 source of oil leaks on the 3.4L, but they have already been done and the first sign that they are leaking is a burning oil smell because they typically leak right onto the exhaust manifolds.

Thanks for the replies and suggestions. The engine's a lot more oily in that pic than it is now but I still need to give it a good cleaning at some point. I forgot that I'd asked the guy to replace cam and crank seals at the time so those should be good. I don't see any leaks around the filter or cooler. I do need to get in there and tighten the remaining VCG bolts but I'm not seeing any dyed oil in that area so I think I'll start with the dipstick o-ring.

I ordered a new dipstick tube o-ring from the dealership and some Aisin gasket sealant from Amazon - the Toyota FIPG wouldn't arrive for a week. Should all be here tomorrow. I'll update with the results after I get it changed.

To really nail down a leak, you need to do a good cleaning of the engine so you can find the fresh oil. The age-old grime can hid things pretty well.

Start with tightening the valve covers - slowly, carefully and work your way around. It is easy to crack the cover if you over-torque it.

Then work your way down. It is possible to have a totally leak free 5VZ... Then you just have to figure out the tricks to a no-spill oil change.

-Charlie

The only other thing in that area is the oil pump. Is it possible it has a microscopic leak? You really should see it if you clean it really good.

Also is there any possibility that when filling the oil up after changing it that oil isn't spilling and running down the engine?

Just the thoughts I had.

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I can honestly say it's not possible I spilled oil when filling after the last change. I'm actually due for another but I was hoping to figure this out while the dye is still in there (but I have another bottle of dye if needed).

I hope it's not the oil pump but it's entirely possible. Drove to the local DIY car wash recently with a jug of Purple Power and a couple scrub brushes but discovered the city closed it down. I'll have to figure out another way to do a thorough cleaning.

The leak appeared after maybe a 5 mile drive previously. I wiped it down again today after replacing the oil dipstick o-ring and didn't see anything after a short test drive. I guess I'll see what it looks like after a longer test drive tomorrow.

It would be great if it was just the dip stick o ring.. as that's an easy fix

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No way Karma's going to let that happen!

I replaced the oil dipstick o-ring and that pooling hasn't returned where I wiped it clean. So I got that going for me, which is nice.



But there's still something leaking. Pic makes it look like the Valdez but it was just a thin layer.



The only VC bolts I haven't tightened are the inside 4 on the left side so I guess I need to investigate further (and earlier - this getting dark at 4:30 thing really grinds my gears). Or could a VC leak on the left side make its way to the right of the skid plate like that?

Changing the oil dipstick o-ring didn't hurt but it sure didn't fix anything.



The dye really makes it stand out.



The main area it's collecting in is the right side of the skid plate, just in front in front of the steering rack.



It seems to be coming from somewhere above that on the right side of the engine but I need to thoroughly clean everything somehow so I can figure out where. I'm way out of my wheelhouse on this one. I suppose I could start by removing the timing belt cover and checking there. Certainly open to any and all suggestions.

The key with finding a leak with oil dye is to start with as clean of an area as possible and then checking for leaks often. I always let it run for a few minutes after adding dye and then rechecking, then I go on a 1 mile trip and recheck, then a 5 mile trip and recheck. You want to find the leak when it's as small as possible to help narrow it down.

It's quite possible that it's coming from a crankshaft or camshaft seal and then finally leaking out at the bottom of the timing cover area.

Plus 1 with Bad Luck as most likely the causes. The only other thing there is the oil pump itself. I can't say I heard of the oil pump ever leaking. Possible I guess

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I'm unfamiliar with the oil pumps on these engines. Are they external in any way to the engine? I'm used to GM oil pumps which are usually internal to the engine so any oil pump leaks never make it to the outside of the engine if that makes sense.