Oil leak - need some direction
 

Truck specs - 1991 4WD Pickup, 3VZE, Manual transmission

History - 3rd party rebuild engine installed at 248k mi be ASCE and Toyota certified mechanic. 255k mi on engine now. Clutch belts hoses and radiator done at that time as well.

Problem - oil and/or tranny fluid all over bottom of bell housing. Last night while in a tough spot, engine suddenly began running very rough while warm. Idle low and uneven. Skipped and stuttered when brought up to revs. Lacked power. Got it to a better spot by running at 4k+ revs in 4lo (I had to be there anyway for other reasons) and killed it and let it sit. Ran fine after that for 35 miles until I parked it.

While it was sitting I got underneath it. The clutch fork boot was out of the bell housing and it looked to me like either motor oil or transmission oil was leaking out of the bell housing. Which is odd - the clutch was not slipping. Transmission and shifting were fine. Oil pressure and level are fine. Engine temp is fine. Slight coolant smell through heater but not exhaust. I'd like to think I do not have yet another failed HG, but given the engine and coolant smell I am nervous (could also be some failure in the heating system which is very old...). What do you all think?

Here's a pic (sorry about size) after I drove it back home after stuffing the failed boot back in:
https://cimg5.ibsrv.net/gimg/www.yot...00eb8f275.jpeg

With oil leaks, gravity is not your friend. Oil goes downhill, so every leak looks like it's the main seal. On the 3VZE, I often hear of leaks in the backs of the valve covers (caused by not following the FSM directions to put spots of RTV in the corners). These all go down hill.

So I would suggest you get a can of spray engine degreaser; use it and a garden hose to get the engine squeaky clean. Start it up and immediately look for a leak.

As you fear, you COULD have a bigger problem, but at least you'll be working on a clean engine!

What do you think of the clutch fork boot popping out? Other than needing to be replaced - just coincidence? Is there anyway exhaust or anything could create pressure inside there?

Probably the valve covers. They leak regularly on 3.0s and make quite a mess when they do. As for the fork boot, it happens. Try to put it back in. I find they swell up pretty bad when they soak in oil and never go back in.

OK. Thank you.

What about the part where it ran super rough, then sat and ran fine? What could cause that?

I'm not real sure where to go with the running problem. We don't really have enough information to have any real direction to head. You can check for any stored codes and see if there's anything visually wrong under the hood. Other than that, its kinda just a waiting game for when it happens again.

It could be both engine oil and gear oil from the transmission. The front input shaft seal and/or seal housing gasket like to leak oil after so many years and miles. The clutch fork boot swells and deforms from oil and you should eventually replace it but only after fixing the leak. Don't worry about it for now, you have bigger fish to fry.

The rear main is probably not leaking or your clutch disk would get contaminated fast and start slipping. When the gear oil leaks, it generally slides down the bellhousing and out the drain hole, not really contacting the clutch. Engine oil from valve covers or head gaskets would largely remain outside of the bellhousing

I recently rebuilt my 3.0 and now in the process of breaking it in. After my first 10 miles it started running really rough. I revved up the rpms a few times then it cleared up. Happened a few more times with same results. Did some reading in the FSM and it said unmetered air in the intake tube between the AFM and the throttle body will cause missing and rough running. So I checked it out and found a crack in the tube at the TB. I took and put some gorilla glue on it. I have not had a repeat of the missing issue. New intake tube ordered from Toyota. A FSM can be your best friend for trouble shooting. Hope this helps.