2000 GMC 1500 5.3 Vortec Oil Leak

[Kdsmith74]

This 5.3 has an oil leak I cannot find. We are at 268K and I don’t know the life for the first 220K. My dad bought the truck with 220K and we swapped it back and forth for a while until we both moved on to other rides. The truck was purchased and while that person had it, this leak started. They parked it for two years and didn’t run it. I finally got it back. It still runs great. Oil leak is pretty bad though. I can’t find the source. From what I can tell It’s not rear main. The bottom of bellhousing is dry, flex plate appears dry through viewing window. The leak is showing up much further back, so my best guess is that it’s leaking from above the bell housing and running down. Most of it accumulates and drips off the corner of the transmission pan around the shifter linkage. I just changed valve cover gaskets and PCV valve while I was there. Leak showed no change before/after VCG change. I am at a loss of where too look next. Oil pressure sensor I’ve seen mentioned online. I got my hand back there and felt around and didn’t come out with any new oil on my fingers. Granted that’s not a very foolproof check. Another note, it only leaks while running. Not sure if that helps. 
 

any ideas on where to check next? 

[CamGTP]

The oil pressure switch and the camshaft sensor o-ring are going to be the main leaks at the very rear of the engine. You could also have leaking valve cover gaskets on the back side.

 

 

 

I would clean everything really really good. Get some degreaser, some oven cleaner, spray it all down and let it soak then wash it all away.

 

You'll probably want to remove the intake manifold to clean everything and replace the o-ring in the back. Good time to do intake gaskets while you're in there.

[Kdsmith74]

Thanks for that. I will work on pulling the intake and inspect. Is there any way to check for leaks once intake manifold is off? The leak is only active with the engine running. I really don’t want to guess work getting this deep but not sure how to check. I don’t want to pull this, change the gaskets mentioned, put it together only to see the same thing. 

[CamGTP]

A probe camera or like a borescope camera would let you see the leak prior to taking stuff apart.

 

I suppose you could disable the fuel pump and unplug the coils with the intake manifold off, then use the stater motor to spin the engine over a bunch. That will engage the oil pump and push oil through the engine but the oil pressure will be far less than when running. It may or may not let you see the leak. There isn't much else to check back there. I rarely see the valley cover gasket leak and drip oil because oil doesn't really get splashed up there nor is it under pressure.

[diyer2]

I believe once the intake is off you will be able to see the leak.]

If it was me with that many miles and if you plan on keeping it I would replace all parts on the back of the motor.

[Kdsmith74]

This isn’t my daily driver, so I am using it to expand my knowledge. I’ve worked on small engines, boat motors and such, but only done accessories previously. I have a decent understanding of how the thing works, but everytime I tear into it, it’s my first time seeing that deep into the engine in person. I’ve watched videos on it all but just not sure what to look at past the obvious. I’ll get the intanke off and see what all I can see. 

[Kdsmith74]

Got the intake off, haven’t had a chance to inspect it all just yet. I had some fresh oil on the pressure sending unit, but the leak isn’t active unless the engine is running so I figure I’ll just be looking for the newest oil I can find. I’ve got my eyes on oil pressure sending unit, can position sensor o-ring, intake gasket. 
 

Is there anything else I should be specifically looking for while intake is off? 

[dna9656]

The pros clean the engine and put a dye in the oil that fluoresces under a black light and run the engine and look for glowing oil. There is some thing about a valve or port on the back of a 5.3 that leaks, mine does I believe. Look into that....

Push comes to shove I suppose you could get a banjo bolt and oil pump feed line on the oil pan drain, put a  an electric pump on the feed line to move the oil at operating pressure, like a pre lubing system....

Edited July 18, 2021 by dna9656
Corrections

[wayne white]

I had a similar problem with my 2003 Silverado 1500 vortec 4.3L V-6.  Turned out to be a blown head gasket.  I was also losing coolant but it didn't show up in the oil.  That turned out to be the water pump.  The bad water pump may have caused overheating which may be why the head gasket blew.  I was told by an old schooler that my year range GM pickups had a problem with head gaskets being manufactured too thin and blowing between 80-100K.

Edited July 18, 2021 by wayne white

[Kdsmith74]

I have thought about head gasket but from what I can tell I am not losing coolant. Granted I can’t run it very long because I’m losing about half a quart of oil by the time I get to operating temp.

 

[Kdsmith74]

I’ve got fresh oil around the oil pressure sensor. Also the intake manifold appears to have been bad, but it’s dry soot, no wet oil on or around the valley cover/knock sensors. 
 

question, oil pressure sending unit works still, but leaking. Is there supposed to be an o-ring or is this metal ring the proper seal? Photo is attached of what I have. Can I seal this anyway or should I just replace?

[txab]

Nope no o-ring, just metal washers. I'm looking at one right now.

 

Leaking sensors that failed internally can be common

 

[Kdsmith74]

Replace it then. Heard that. Now that you mention it, I think there was some oil up top when I removed the first plastic connection. I thought it was normal but an internal failure makes sense. 

[CamGTP]

Get an OEM sensor too. I know they cost more but I've had so much trouble with aftermarket sensors in the past. The $30-40 parts store sensor always die.

[Kdsmith74]

Just wanted to post a major thanks to you all for the input. Got it put back together with new oil pressure sensor, cam position sensor o-ring, and intake gasket. Along with valve cover gaskets that i did prior to this post. we appear to be leak free, and come to find my oil pressure sensor was bad. i has been sitting around 35 on a cold start but with the new sensor I am now reading around 55 at cold start. thanks for the knowledge shared!!