Rear Main leaking, vented oil cap?

[02Lightning]

So it looks like I have oil inside my transmission inspection cap, meaning I have a rear main leaking. I called around to see how much to replace, and one garage said that when they looked it up, there is service bulletins saying to clean the PCV system and change to a vented oil cap.

She gave me part number 12589430 it try before changing the seal. I looked the cap up and doesn't look to fit my truck? Also, has anyone heard of this on my year truck? One thing that crossed my mind too, is replacing the drivers side valve cover, but everything I've heard on this is when clogged it will increase oil consumption. I haven't notice any increase in oil consumption. I've got about 133k on the truck now.

 

[thompsoj22]

I would find a different shop, That is old school and not a solution for your "modern" engine. At 133k it is possible the seal is worn, when you look inside the bellhousing can you see the oil path on the block coming straight down the center of the engine? could also be a valve cover gasket, oil pressure sending unit leaking from the top. Either way find a new shop, the rear main is a pita for any mech simply based upon R&R of the trans to get to it. If it isnt pissing than live with it? you havent changed brands of oil lately have you?

 

[02Lightning]

I would find a different shop, That is old school and not a solution for your "modern" engine. At 133k it is possible the seal is worn, when you look inside the bellhousing can you see the oil path on the block coming straight down the center of the engine? could also be a valve cover gasket, oil pressure sending unit leaking from the top. Either way find a new shop, the rear main is a pita for any mech simply based upon R&R of the trans to get to it. If it isn't pissing than live with it? you haven't changed brands of oil lately have you?

It's been a while since I've looked in the transmission cap, but I do recall oil inside there, but not sure if it looked like it was coming straight down the center. Before I have anyone do anything, I'm going to replace the oil cooler block off gasket, and maybe the crank position sensor. The valve covers don't look bad, but I have the gaskets to replace those, and I'm going to replace the drivers side valve cover while I'm at it. My first thought when she said vented, is it's a closed system and would give me a check engine light. I was running Mobil 1, this last time I changed oil I switched to Valvoline, but not sure I've notice more of a leak or not.

 

[iamdub]

As suggested, first verify the source of the leak. With the multiple possible leak points all around back there, a leaking rear main is commonly misdiagnosed and the actual repair is a much easier/cheaper sensor or gasket. Us a bright light and, through the inspection hole, look between the flex plate and rear engine cover. If the RMS is leaking, there will be a trail. Due to the wind currents under the vehicle and in the engine bay, oil dripping from higher up or from the side can be blown back and collect in other areas and lead you to believe something else is leaking.

A vented oil cap will cause an SES light due to loss of crankcase pressure. If you have a clogged PCV system, fix that rather than try to purge the air elsewhere. If your driver's side valve cover is original, it's likely the design that has been updated to solve an oil consumption problem. Since you already have the gaskets, have the new updated cover ready for when you go to install them. This would also ensure you have a clear PCV port since that comes mounted in the cover. It's not a valve with any moving parts, just a fixed orifice. The design of the PCV system (inlet on the passenger side, outlet on the driver's) keeps the flow going in one direction.

 

[Bill 1960]

Unless it’s losing a noticeable amount of oil, I’d just live with it. I’ve had a Jeep with a weeping rear main for four years, but it’s just a nuisance leak. Doesn’t require any refills between oil changes so there’s no way I’m pulling the trans out just for that.

I would check the PCV system because that can cause all sorts of seal and gasket issues.

I’d also remove the oil filler cap at idle and check for blow-by just in case you’re getting some worn rings, which can pressurize the crankcase too.

 

[donjetman]

OP, Find another garage.

GM came out with a new improved valve cover yrs ago. My guess is you need install it, GM# 12570427 for 2007-08. Made a huge difference on mine. Here a thread I started:
https://www.tahoeyukonforum.com/threads/valve-cover-change-cleanup.108604/

My engines rear main seal was bad too. Here's a thread I did on that subject too:
https://www.tahoeyukonforum.com/threads/engine-oil-pan-gasket-change-6-2-yukon-l92.108487/

 

[davidavidd]

Check your Camshaft Position Sensor (passenger side, above the starter), it's a common oil leak source too.