This has me stumped...

...along with my mechanic.

I have a 1999 Nissan Frontier 4 X 4 pickup with 112000 miles. It has never given me one bit of trouble and other than normal maintenance has never been in the shop for mechanical problems, until now.

It has developed an oil leak. Nothing major, but a leak just the same and I hate oil leaks! I crawled all over that engine compartment and I couldn't find one spot where there was any indication of a leak. Crawled under and found a small leak out of the transfer case drain plug so put some sealer on the plug stuck it back in and no more leak, or so I thought. I took it to the local mechanic, who is very good and very reputable and had him look at it. He found some oil on a cross member, maybe spilled there during an oil change, so he wiped it all off and said that's the only thing he found. OK, I'm happy no more leak!

Couple days later, oil on the driveway again. Now this is where I get stumped for an answer. If I park the truck in the driveway like I normally do, by pulling in, no oil leak. If I back into the drive it leaks. By backing into the driveway the front of truck would be sitting at a slight downward angle. If pulled in it would be at a slight upward angle. Any ideas where this leak may be coming from!?

 

Old time trick would be to sprinkle/blow some baby powder/talcum powder on the engine in the general area you think the leak may be. Back in the drive and check the next day or two. A dark streak in the white powder should lead you right to the source.

 

If I had to take a wild guess, I'd say oil pan gasket on the front.
If you can, give the underside a good clean and wipe down, then back into the driveway.
When you check it, don't move the truck, just get under and look what is directly above the spot. You should see some marks where it's leaking.

Have you confirmed it's oil and not another fluid?

 

That's what I was wondering- if it's a different fluid. Seals at spinning parts are grooved and I'm wondering if it's some kind of driveline seal, so when the transmission yoke or transfer case or the differential or something goes into reverse, it draws a bit of fluid out...

 

1. oil pan leak
2. main seal leak
3. head gasket leak that seeps down
4. valve cover leak.

either do the baby powder thing or add contrast dye to oil and scope it with black light.

 

I'd be inclined to pull it into the driveway but put the front on ramps so it is inclined from front to back and gives you room to crawl underneath. That way, you might be able to see the leak when it's happening.

 

These are all good suggestions, and things I or my mechanic have done. Neither of us can find a leak in any of the places mentioned, oil pan, valve cover gaskets, main seal or head gaskets. The mechanic has done the dye/black light and found nothing. Cleaned the bottom of the engine, trans and transfer case. Only thing found was a small leak from the fill hole in the transfer case and some oil on a cross member, probably from an oil change spill when the filter was removed and not wiped out. Transfer case plug leak was fixed and the oil on the cross member wiped up.
Now I beginning to get a very slight smell of burnt oil in the truck. Can't smell anything outside just inside and it is just a very, very light smell. My wife says it's my imagination cause she says she can't smell anything. It could be coming through the heater, I've not paid close attention to see if it's when the heat is on or off.

 

I did have a leak in one car that was the oil pressure sending unit, leaking through past the wiring harness. It would leave one or two drips at the most.