Checking Possible Rear Main Oil Leak at Bellhousing

[hogosmith]

I've been going over a lot of discussions about chasing oil leaks down. The question I have is: if the front of the flexplate is clean and dry, does this rule out a rear main seal leak?
I have the typical oil drip at the rear of engine and front of bell housing area. When I cleaned everything and then came back later it looked like it was first coming down from the oil pan on the starter side, then working down to the bell housing bolts.

Mine is a 2004 Z71 with 5.3 and 4L60e with about 158,*** original. I had the tranny rebuilt in Dec. 2020. Don't know if it is connected but the car did not leak at all before the tranny work.

I'm trying to get armed with all the stuff I can do at home, before I have to start saving up for a shop visit... Maybe replace the oil cooler bypass plate/gasket, check the oil sensor unit and the cam position sensor, check valve cover gaskets... Anything else ? Sidenote: I'm thinking about replacing the oil sensor unit as I'm getting a lower pressure reading than before... Before - 40+ PSI at hiway speeds and 25-30 ish PSI at idle. Now it's about 30 PSI at hiway and below 20 at idle. This has happened over the course of about 5k to 6k miles and one oil change. I use Synthetic 5 - 30 wt (Valvoline, I think) and a Mobile One oil filter. I am on a fixed income/tight budget, so yes I do shop prices... Sorry for rambling. (smile)

 

[SnowDrifter]

Flex plate: Not necessarily. That only means it's not dripping onto the flex plate. But there's no law saying the oil has to travel from shaft to flex plate.

Oil pressure: change the oil again. See what happens. Could be filter plugging up, oil shearing down, gauge being funny, fuel contamination.

Oil leak: The car's old enough to vote. I don't think a year between transmission and an old gasket leaking is causative. Gaskets don't last forever. With that said, one of my favorite ways to track down an oil leak is to run to the auto parts store and get some UV dye. 5 or 10 bucks for a bottle. Toss it in with the oil, run the motor, and start shining a blacklight around. There is zero ambiguity as to where stuff is coming from.

As far as stuff behind the engine to leak or for oil to travel to:
- Oil pan gasket
- Cooler bypass
- Drain plug
- Rear cover
- Rear main
- Oil pressure sender (top)
- Head gasket
- Valve cover gasket
- PCV
- Oil filter
- Valley pan gasket (top)
- Knock sensors gasket against the valley pan
- Camshaft position sensor (top)
- Crankshaft position sensor (by starter)

For what it's worth: you don't need to remove the intake to get to the oil pressure sender. Chrome socket and a swivel extension that's just the right length will let you do it fairly easily by feel.

Shot in the dark.... Go Cougs?

 

[Fless]

Mine is the Flex Fuel so I know that the fuel lines are a bit different and might get in the way, but I didn't even have to use a swivel when changing the oil pressure sender. Flex head ratchet can be useful. YMMV

 

[hogosmith]

Thanks for all the input and things to look for, leakage -wise. I like the idea about the dye and black-light.

I've been a shade tree mechanic since the days of first generation muscle cars, so anything I can do to keep from getting out the BIG checkbook, I'm up for. But it is getting hard to get back up from under a car these days... LOL

This is Cougar country yes... I'm about 2 hours from WSU, down near Walla Walla.

 

[Rocket Man]

There’s nowhere worse that being under a car that’s not on a lift. Looking forward to what you find out.

 

[corvette744]

I 2nd the use of uv dye takes less than an hour to properly diagnose any leaks anywhere.You have to change the oil anyway im guessing.

 

[hogosmith]

"I 2nd the use of uv dye takes less than an hour to properly diagnose any leaks anywhere.You have to change the oil anyway im guessing."

Yes, I'm going to change oil/filter, but first try to do a solid UV dye test. Then go from there... Probably be a couple days before I can start. The weather turned last night with big winds and sideways rain.

I'll keep you all posted. And thanks again for all the input/advice. Appreciated