Strange oil leak on 383 with TH350 - Team Camaro Tech
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post #1 of 23 (permalink) Old Jun 12th, 19, 07:17 AM Thread Starter
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Alex
 
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Strange oil leak on 383 with TH350

Hi folks,

i'm tracing a very strange oil leak.

What's my setup?

New (500 miles) ATK 383 stroker crate engine with new TCI Th350. For those who think about too much pressure inside engine: i'm running an adjustable PCV Valve. With a standard PCV, the problem was the same.

Where do i find the oil:

Dripping of the lower bell housing cover & i can find oil between engine and trans near the starter (passenger side) and near the oil filter (driver side).

How much oil?

It's enough to leave a 5 inch diameter (maybe 15 drops) amount on the garage floor every time i drive (it then stops after sitting for a while) and cover the bell housing cover, trans pans etc.

What did i already check?
  • No oil on flex plate - bone dry - from what i know this means i don't have a rear main seal leak
  • No oil on distributor seal
  • No oil on valve cover gaskets (also back at firewall), also retorqued the bolts
  • No oil on oil pressure sender/sensor (mechanical)
  • Little oil on spark plugs (strange...) - i did retorque them, there were a little loose, but another test run showed oil again - but not enough to create that much oil on the bell housing
  • When i try to trace it from starter/oil filter up the engine with my fingers, i don't "feel" any noticeable amout of oil.

So here i am being annoyed and more.

Can anyone help me, give me a hint oder tell from experience?

Thank you very much!

Alex

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post #2 of 23 (permalink) Old Jun 12th, 19, 07:28 AM
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Re: Strange oil leak on 383 with TH350

Sounds like you blew out the gasket at the rear china rail on the top of the block.

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post #3 of 23 (permalink) Old Jun 12th, 19, 08:02 AM Thread Starter
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Hi Dave,

thanks! You mean the gasket between intake and block at the firewall?

Should be able to "feel" the leak Witz my hands. I'll check that.

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post #4 of 23 (permalink) Old Jun 12th, 19, 08:05 AM
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Re: Strange oil leak on 383 with TH350

^^^. OP, you can buy oil dye kit which has a black light. Oil will glow neon green using light & glasses in the kit

New motor and oil is hard to trace a stubborn leak

do you feel any oil running fingers along rear china wall?

FWIW that is where I thought my leak was coming from as leak was similar to yours (covered starter, dripped from lower center of BH. It turned out to be valve cover gasket...after I re-did intake gasket.

I use Permatex Black "ultra" RTV on China walls

Got these for VC gaskets....they sealed the VC leak

https://www.autozone.com/external-en...253_35483_6534
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post #5 of 23 (permalink) Old Jun 12th, 19, 08:44 AM
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Re: Strange oil leak on 383 with TH350

An old school trick is throw flour onto suspected area for leak detection.
Flour will change to a darker color, of course.

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post #6 of 23 (permalink) Old Jun 12th, 19, 09:02 AM Thread Starter
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I just checked the chinese Wall - bone dry (Front and Back). Seems like ATK used rtv or a silicone gasket.

Always thought about valve covers but they are just dry....

Using a dye light is an option, but i'd like to first check some more options.

Using powder sounds good - worth the try.

Any other ideas?

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post #7 of 23 (permalink) Old Jun 12th, 19, 09:10 AM
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Re: Strange oil leak on 383 with TH350

just had exact same symptoms and turned out my rear main seal was the culprit. relatively new build engine and machine shop installed the two halves of the seal in opposing directions. i know it's not what you want to hear but it may be the case. i didn't have any oil on the actual flexplate either. but if you can get in there with a boroscope or flashlight, you may see oil splattered in at star pattern on the back crank flange that rides on the outside of the block. it will typically throw the oil from a rear main leak to the passenger side due to engine rotation and it usually winds up all over the started then drips down the pan and it'll get all in the bellhousing and all over the exhaust. look close at these pics of the way the shop installed my seal. hopefully that's not your issue, but it sounds like it is.
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post #8 of 23 (permalink) Old Jun 12th, 19, 09:47 AM
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Re: Strange oil leak on 383 with TH350

Quote:
Originally Posted by wrekki View Post
Using a dye light is an option, but i'd like to first check some more options.

Using powder sounds good - worth the try.

Any other ideas?
new motor painted with fresh oil and a relatively slow leak and at this point you can't confirm where it is coming from.....well you can start throwing new gaskets at it....or get a dye kit as it will VERY clearly show you source.

flour is old school and works "if" you can get the flour on the core source of leak and if so actually see the discolored flour

at this point you and the rest of us are just guessing as to where the more common leak sources are

pour the dye in, drive for about 15 min, pull car in garage and let cool. Best to check in darker environment and you should get the car up on jackstands as you will likely discover the leak source from under the car. It will lite up like neon green when you see oil. Follow the trail

There are dye "kits" that have various fluids for different parts of car (AC, oil), pair of yellow lens glasses and a UV flashlight (aka black light). Most auto part stores either have these things sold separate or in kit form. IIRC I got mine at Harbor Freight. Gonna cost WAY less than throwing new gaskets at various places let alone time

Your note about finding oil on/near spark plug base to me screams VC....but IMHO you need, at this point, to use something that will reveal the leak source

Sadly if it is RMS...everything come out of the car
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post #9 of 23 (permalink) Old Jun 12th, 19, 01:11 PM
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Re: Strange oil leak on 383 with TH350

Rear main, there are also three oil galley plugs by the cam plug on the back that can leak.

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post #10 of 23 (permalink) Old Jun 12th, 19, 01:12 PM Thread Starter
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Re: Strange oil leak on 383 with TH350

@bhodgdon400: interesting news, that there does not have to be oil on the flexplate. And yes, i didn't want to hear that

In the end i'm convinced now that searching with dye is the best next step. I ordered some and will take it for a ride when i have the time to investigate.

I will then come back here and tell the results.

Thanks for your quick help guys!
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post #11 of 23 (permalink) Old Jun 12th, 19, 01:14 PM Thread Starter
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Re: Strange oil leak on 383 with TH350

Quote:
Originally Posted by ilikeike View Post
Rear main, there are also three oil galley plugs by the cam plug on the back that can leak.
How can i distinguish those from the RMS without the trans being disconnected?

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post #12 of 23 (permalink) Old Jun 12th, 19, 01:21 PM
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Re: Strange oil leak on 383 with TH350

Quote:
Originally Posted by wrekki View Post
How can i distinguish those from the RMS without the trans being disconnected?
If you determine that it's coming from the back of the engine, you'll be pulling the trans to pin point and fix.

I'd maybe clean the engine real well, then put the car on jack stands run it and try to watch where it's coming from ?

Hopefully it's something easily fixed without pulling major components.

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post #13 of 23 (permalink) Old Jun 13th, 19, 02:17 AM
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Re: Strange oil leak on 383 with TH350

In looking at the pictures the OP posted in post #7, isn't this correct for a main seal? Meaning, the seal ends are not supposed to be flush to the bearing cap and block, but rather slightly offset as shown in the picks. Books on rebuilding various engines always mentioned offsetting the rear main seal slightly.

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post #14 of 23 (permalink) Old Jun 13th, 19, 06:29 AM
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Re: Strange oil leak on 383 with TH350

Quote:
Originally Posted by wrekki View Post
Hi folks,

i'm tracing a very strange oil leak.

What's my setup?

New (500 miles) ATK 383 stroker crate engine with new TCI Th350. For those who think about too much pressure inside engine: i'm running an adjustable PCV Valve. With a standard PCV, the problem was the same.

Where do i find the oil:

Dripping of the lower bell housing cover & i can find oil between engine and trans near the starter (passenger side) and near the oil filter (driver side).

How much oil?

It's enough to leave a 5 inch diameter (maybe 15 drops) amount on the garage floor every time i drive (it then stops after sitting for a while) and cover the bell housing cover, trans pans etc.

What did i already check?
  • No oil on flex plate - bone dry - from what i know this means i don't have a rear main seal leak
  • No oil on distributor seal
  • No oil on valve cover gaskets (also back at firewall), also retorqued the bolts
  • No oil on oil pressure sender/sensor (mechanical)
  • Little oil on spark plugs (strange...) - i did retorque them, there were a little loose, but another test run showed oil again - but not enough to create that much oil on the bell housing
  • When i try to trace it from starter/oil filter up the engine with my fingers, i don't "feel" any noticeable amout of oil.

So here i am being annoyed and more.

Can anyone help me, give me a hint oder tell from experience?

Thank you very much!

Alex
Make sure your cam did rub a hole in the cam button in the rear of the block. Had that happen on a Z/28 once. Had it Helicoiled but that didn't really fix it, ended up getting a new engine.
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post #15 of 23 (permalink) Old Jun 13th, 19, 07:42 AM
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Re: Strange oil leak on 383 with TH350

Quote:
Originally Posted by bucko View Post
In looking at the pictures the OP posted in post #7, isn't this correct for a main seal? Meaning, the seal ends are not supposed to be flush to the bearing cap and block, but rather slightly offset as shown in the picks.
You are correct in your statement shown above... but the photos in post #7 show that the lip seal on the main cap is installed 180 in the opposite direction as the lip seal in the block. I believe the seal in the cap needed to be removed and reinstalled so both lips were facing the same direction.
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