Truck leaks oil only while running

[Tpanda]

I noticed a few weeks ago that my truck leaks oil but only when running. Its a Z22 motor.

It appears to be leaking between the transmission and rear main seal. My problem is that I already replaced the rear main seal a few months ago when I installed a new clutch. Also, Ive never known a vehicle to leak oil only when running.

Does the transmission have a seal in the front housing? Its a manual so I doubt it has a front pump seal of any sort.
It also doesnt smell like gear oil which has such a distinct smell.

I know the valve cover gasket needs to be replaced. Maybe the half moon is leaking? Wouldnt it leak all the time though?

Maybe the truck running causes the leak to be worse but I havent had to add any oil yet. I dont drive the truck much because Im still tracking down some stalling issues. Brake booster and master cylinder were leaking air and now i think i have a fuel delivery issue. Truck idles great, under brake load and driving the truck stalls out but always fires right back up. It will idle all day until you rev it up, then it stalls out when returning to idle.

[PEZi]

My guess is that the rear main may need a second look. To be leaking only while its running would suggest, however, that oil pressure is causing the leak. Yes, there is a front main on the trans, but that wouldn't make sense because it would leak all the time.

[breadbox]

Half moon is on the head and it would have to fill the head with oil out of the pan before it can leak from the moons, so it'd have to run to do that. I second rear main, I always replace it if I have the flywheel off for any reason. They are cheap insurance.

Are you stock carb? Test your fuel pressure, do you have a mechanical fuel pump?

[Tpanda]

Half moon is on the head and it would have to fill the head with oil out of the pan before it can leak from the moons, so it'd have to run to do that. I second rear main, I always replace it if I have the flywheel off for any reason. They are cheap insurance.

Are you stock carb? Test your fuel pressure, do you have a mechanical fuel pump?

Stock carb, 3 piece hitachi. Every vacuum line is plugged besides the brake booster and distributor advance. I believe its a mechanical pump but Im not a 100%. I noticed fuel leaking near the fuel filter (the one by the bed of the truck where the bed meets the cab passenger side) and I have two theories. 1) Fuel filter is clogging cutting the truck off when trying to return to idle. 2) fuel line is cracked/broken/ or missing and sucking air leaning the truck out.

I replaced the rear main when I did the clultch. I tore up two of them because I didnt have a socket big enough to fit over the crank while putting it in. I finally got the third one in flush with no visible damage.

I did all of it on my back with two friends helping me. Not a job I want to tackle again without a lift.

Im not going to fool with rebuilding that carb, saving up for a Weber.

I should add that the truck sat for 6 years. These stalling issues started coming up the more I drove it. Ive only put maybe 50 miles on the truck since doing the clutch after bringing her back to life. I suppose its either stuff breaking or starting to fail. : :

I did all the tune up stuff. New gas, coolant, oil, plugs, wires, caps, rotor buttons.

[breadbox]

like you said, it leaks fuel. that's an issue. I replaced my fuel filter pretty early on, just to be safe. Its pretty easy to replace all that, unless your hard lines are rusted out. Like they were on my friends 240sx.

[Tpanda]

Fuel lines are not rusted. I think its the rubber fuel lines coming off the fuel filter.

I only saw it leaking twice and havent noticed it sense. Fuel filter and lines are on the to do list, so much is needed before that.

[breadbox]

Do it now or at least sooner than later, I mean its a few dollars in fuel line and a few dollars in hose clamps, throw down on a new fuel filter(its tiny), If your truck is stock height you don't even need to jack it up or down, just replacing a few things with basic hand tools.

[Tpanda]

Do it now or at least sooner than later, I mean its a few dollars in fuel line and a few dollars in hose clamps, throw down on a new fuel filter(its tiny), If your truck is stock height you don't even need to jack it up or down, just replacing a few things with basic hand tools.

its stock height. You can clearly see the fuel filter when standing by it. You're right, its only a few bucks. Ill knock it out tonight.

[Tpanda]

Do it now or at least sooner than later, I mean its a few dollars in fuel line and a few dollars in hose clamps, throw down on a new fuel filter(its tiny), If your truck is stock height you don't even need to jack it up or down, just replacing a few things with basic hand tools.

its stock height. You can clearly see the fuel filter when standing by it. You're right, its only a few bucks. Ill knock it out tonight.

[Kahmael]

Did you ever find the solution to the leak when running? I'm having the same issue, and It blows through oil pretty fast.

[Rev_D21]

The only spot it could leak oil from back there is the rear main seal.

[Tpanda]

Never found the issue. I never went through oil so I think it was trans fluid even though it wasn't low. Haven't noticed the leak in a few oil changes. Maybe the rear main finally seated or doing the valve cover gasket job sealed it off and it stopped the leak.

Ethol is current parked waiting for a ka swap. Donor motors came out of 1992 d21 pickups. Both two wheel drive and both manuals. Have to get the block cleaned, crank polished, and the heads rebuilt and then start the motor build. I have all new chains, idlers, and guides as well as the cover. The guide snapped and chewed the cover up. It ran we dropped the motors.

I bought a 2008 four door soft top jeep wrangler to get me by until then. Lol.