Elusive engine oil leak

[Daniel B Martin]

2004 GMC Yukon SLT
VIN 1GKFK16Z54J122888
5.3L V8 Bone stock


A nasty (and worsening) engine oil leak. Drip, drip, drip while the engine is running. Not a rear main seal leak, the drips are coming off the head of a starter motor mounting bolt. There is no engine oil inside a starter motor, so the source of the leak is somewhere above, and on the passenger side.

Advice from various forums suggested a leaky engine oil pressure sensor. That sensor is at the rear top of the block in a difficult-to-see location. However, it looked dry. I replaced the sensor anyway.

Advice from various forums suggested a leaky valve cover gasket. However, it looked dry. I replaced the gasket anyway.

Advice from various forums suggested a leaky oil pan gasket. However, it looked dry. None of the pan bolts were loose.

The leak persists! What should I try next?

The engine starts and runs well, does not lose coolant, so there are no obvious signs of a failed head gasket.

 

[Fless]

Pull the starter and be prepared to replace the crankshaft position sensor. If that's the source of the leak and after that is changed, a cam-crank correlation procedure should be done to help prevent misfires. Not always necessary, but highly recommended.

If that's not the source of the leak, clean the area behind the starter and use some powder foot spray on the area. Run it for a bit to see if that indicates any other sources.

 

[972sparky]

I had a 2008 5.3 that had oil dripping from the same areas, was the rear main seal.

 

[RAMurphy]

I hope it is the more simple fix by changing the crankshaft position sensor. That rear main seal will require pulling the transmission.

 

[Daniel B Martin]

Pull the starter and be prepared to replace the crankshaft position sensor. If that's the source of the leak and after that is changed, a cam-crank correlation procedure should be done to help prevent misfires. Not always necessary, but highly recommended.

If that's not the source of the leak, clean the area behind the starter and use some powder foot spray on the area. Run it for a bit to see if that indicates any other sources.

Thank you, Fless, for a good lead. The location of the crankshaft position sensor matches the observed drip drip drip. I'm working outdoors so will hope for a warm day soon. This Yukon is not my daily driver so I can wait for a while.

 

[89Suburban]

Pull the starter and be prepared to replace the crankshaft position sensor. If that's the source of the leak and after that is changed, a cam-crank correlation procedure should be done to help prevent misfires. Not always necessary, but highly recommended.

If that's not the source of the leak, clean the area behind the starter and use some powder foot spray on the area. Run it for a bit to see if that indicates any other sources.

Damn I thought he dropped that bolt into the bell housing, had to rewatch it LOL.

 

[treehan77]

Likely still rear main seal, but , yes, you can check the crank sensor. Probably not it though, RMS can sling it

 

[Logani]

I have the same leak. It seems like the rms is leaking and the oil is running along the lip of the oil pan and then dripping out at both corners: under the oil filter and under the starter. Oil pan is also leaking from the front but the deluge is definitely rear engine, unfortunately. Pretty sure it the rms. I've just been in denial because I'm not looking forward to wrestling the trans. Please let me know what you find.

 

[89Suburban]

I have the same leak. It seems like the rms is leaking and the oil is running along the lip of the oil pan and then dripping out at both corners: under the oil filter and under the starter. Oil pan is also leaking from the front but the deluge is definitely rear engine, unfortunately. Pretty sure it the rms. I've just been in denial because I'm not looking forward to wrestling the trans. Please let me know what you find.

I'm in the same boat. Just going to keep dumping oil in it. I envy you guys with the 2WD. I might attempt it myself if mine was.

 

[Logani]

I'm in the same boat. Just going to keep dumping oil in it. I envy you guys with the 2WD. I might attempt it myself if mine was.

I can't keep putting oil in it at $8/qt. I'll never have to change the oil but it's a hellova mess and I worry about it lighting up on the exhaust. Glad I'm 2WD, too. Gonna be replacing the oil pan gasket when I drop the trans.