My 408 is up and running but not without problems. My main concern is an oil leak coming from the rear the engine. I can not pin point it exactly, but he's the strange part. It doesn't start leaking until I have shut off the engine?!?! Weird huh? I can't figure it out. Maybe one of you have experienced similar problems. Any help would be great!
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Ok I looked into it further. It appears to leak from the front and rear of the engine and it also leaks with the engine running. I still can not tell where the oil leak is coming from. I fear that the front and rear seals may be bad. I bought this longblock new so it is hard to believe the seals are already bad. No miles ont he engine BTW. I did support the engine on the flexplate with a jack and a 2x4 when the trans was out. Can that have caused any damage??

 

It had the potential to bend or warp the flexplate, but it shouldn't have started a leak. Unless the engine sat a long time, or the seals weren't oiled at assembly time, they are the last items I would suspect. First, of course are the intake end seals. Then, there all the other possibilities. Freeze plugs, valve covers, even the distributor. Good luck, and...

RACE ON!!!

 

Did you use the thick front seal on the pan?

 

The pan was already installed then I purshased the longblock. It looks like they used a thin cork type gasket.

 

After my recent rebuild, I have a leak from a rear oil gallery plug above the cam plug.

 

Any more suggestions would be appreciated. The oil is leaking off the front crossmember and near the oil filter in the rear. Anybody??? I need a lift!

 

Sounds like the same oil leak on my LT1. Been leaking since I bought it 3 yrs ago and getting worse. Last winter I pulled off the water pump and saw oil around the water pump drive shaft. Replaced that seal, but didn't have the pullers to remove balancer so I hoped the water pump shaft was the leak. WRONG. Still leaking. I think its the oil pan seal at bottom of timing chain cover. The guy who rebuilt my engine before I bought it installed a 8 quart oil pan, so he might have screwed up when mating pan and chain cover. This will be this winter's project. Good luck with your leak. John

 

First thing to do is diagnose; second thing is to fix it.

You'll need to jack up the car as high as the four jackstands will allow. Yes, four stands, one at each corner of the car with the car a level as it would normally be when sitting on the tires.

With the car on the stands, first shake the car vigorously to make sure it's stable.

Now crawl under on your back with a couple of can of spray carb cleaner and some clean rags. Spray everything that is oil soaked and wipe away any oil that remains with the rags.

Start the engine and crawl back under with the engine idling and use a drop light to try to see where the oil is leaking from. If you look long and hard enough you will see the source.

Most times oil leaks low on the engine are from the front and rear oil pan gaskets. The point where the oil pan and the timing chain cover meet AND where the oil pan seals against the rear main cap are the likely locations.

One other possibility is that the rear main seal was installed backwards. If yours has a two piece rear main seal, the lips should face toward the front of the engine. You'd need to drop the oil pump and rear main cap to verify this. I'd only resort to doing that if I determined that the pan gasket wasn't the cause.

If it is the pan gasket, get a one piece gasket as a replacement, not the four piece type which are prone to leaking. Be sure to clean any oil from both the block and the oil pan rails when replacing the gasket.

Be careful while you're under there; most of the stuff will get HOT; the flex-plate/converter will be spinning at the back and the crank pulley/damper in the front.

Keep us posted.

Jake

 

Jake,
I will put her up on jacks tonight if I have a chance. I already bought a one piece felpro rubber oil pan gasket. Is there anything else I shoud look for while the pan is off? Thanks for the help BTW.

 

The other things I can think of are:

Where the dip-stick tube fits into the oil pan. I didn't list that before because you said the leak was at the front and rear of the pan and the tube is about midway.

There's a plug that screws into the front of the block, lower passenger side right near where the mechanical fuel pump would bolt (but on the front of the block NOT the side) that sometimes leaks if thread sealer isn't used on the plug. You can check that too.

Sometimes leaking valve cover gaskets can cause a leak that may seem to be coming from the bottom of the block. With the valve covers still installed, run your fingers (or a clean white rag/towel) under the out-board lips of the valve covers. If you get oil on your fingers/towel, the valve cover gaskets aren't sealing well.

For the rear leak, be sure to check the intake mainfold to block seal at the very back. If the person who installed the intake used the gaskets supplied in the intake manifold kit, instead of using a bead of silicone on the front and rear (china walls) leaks often result.

Not sure of the year of the system we're working with, but on mine there is an oil pressure sender and switch screwed into the block are the very rear, just to the driver's side of the distirbutor. If sealant wasn't put on the threads, it'll leak too. then the oil will run down the back of the block and seem to be coming from down low.

Right next to the sender/switch there is a recessed hex-head plug that screws into the block; again, without thread sealer leaks can occur there too. You can only access that plug from the top though. So be sure to spray that area with your carb cleaner then check it for any sign that oil has returned.

There should be a paper gasket between the distributor and the intake manifold; if left out, leaks can occur there too.

There are a few other places that can cause leaks at the rear too, but getting to those requires unbolting the torque converter and removing the flex plate. Let's wait until we see the outcome of the oil pan gasket check before jumping into that.

When cleaning off all the oil with the spray, start at the top of the engine and work your way down; let gravity work for you in washing away the oil.

Keep me posted.

Jake