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LT1 Oil Leak


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My 1997 LT1 Firebird has developed an oil leak again...From the rear of the intake manifold..I've fixed it correctly with great attention to detail twice already ...Once in 2005 or 06...Then again in 2014..Now it has started seeping again...This is common problem with these engines...So I'm going to pull the intake (pain in the ass) again... Was wanting to know If anyone out there has come up with a permanent fix for this issue...?? Or am I just destined to have to redo it every few years...??

Any input or suggestions would be appreciated....

Thanks..TLBT

Edited by TWO LANE BLACK TOP
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2 hours ago, TWO LANE BLACK TOP said:

My 1997 LT1 Firebird has developed an oil leak again...From the rear of the intake manifold..I've fixed it correctly with great attention to detail twice already ...Once in 2005 or 06...Then again in 2014..Now it has started seeping again...This is common problem with these engines...So I'm going to pull the intake (pain in the ass) again... Was wanting to know If anyone out there has come up with a permanent fix for this issue...?? Or am I just destined to have to redo it every few years...??

Any input or suggestions would be appreciated....

Thanks..TLBT

Two Lane, I don’t know what your approach has been to try and resolve this, but my thought would be this! Also I don’t know what end gaskets you are using,I.E. cork, neoprene or just rtv! You might try the following. I would use cork end gaskets with the red rtv! Put a thin layer of the red rtv on the block, than while still wet place the cork gasket into the rtv, but don’t press it in to the rtv hard, and let it cure over night! Next day put another thin layer on the top of the cork gasket! Set the intake manifold in place while wet, install the bolts to align the manifold properly, but don’t bolt it down, just tighten them till they engage the manifold surface! Again let it cure over night, than torque down the next day! 

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Last indian..

Thanks for the response...

The Gen2 LT 1 engine block and intake manifold are of a different design from the old school small blocks and instead of having the traditional cork/neoprene gaskets across the front/rear of the block...Between the cylinder heads...The Gen2  block and the bottom of the intake manifold are machined flat and fit tightly together with zero clearance between them and they are sealed with a copper type Rtv sealant...The only gaskets are the ones that seal the cylinder head intake ports and the manifold...Unlike the traditional small block No water flows thru the intake manifold..Instead there is a pipe that connects the Cylinder heads together for the coolant flow on the rear of the engine...(The engine has a reverse flow cooling system) with the water pump driven off the camshaft...

So I guess what I'm asking is..Is there maybe some kind of a nuclear space age super sealant RTV that will last for millions of heat cycles...and cope with the different expansion/contraction rates of the cast iron block and the Aluminum intake manifold....(Which is the point where the reoccuring leaks are happening)   That is commercially available...?? 

Edited by TWO LANE BLACK TOP
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1 hour ago, TWO LANE BLACK TOP said:

Last indian..

Thanks for the response...

The Gen2 LT 1 engine block and intake manifold are of a different design from the old school small blocks and instead of having the traditional cork/neoprene gaskets across the front/rear of the block...Between the cylinder heads...The Gen2  block and the bottom of the intake manifold are machined flat and fit tightly together with zero clearance between them and they are sealed with a copper type Rtv sealant...The only gaskets are the ones that seal the cylinder head intake ports and the manifold...Unlike the traditional small block No water flows thru the intake manifold..Instead there is a pipe that connects the Cylinder heads together for the coolant flow on the rear of the engine...(The engine has a reverse flow cooling system) with the water pump driven off the camshaft...

So I guess what I'm asking is..Is there maybe some kind of a nuclear space age super sealant RTV that will last for millions of heat cycles...and cope with the different expansion/contraction rates of the cast iron block and the Aluminum intake manifold....(Which is the point where the reoccuring leaks are happening)   That is commercially available...?? 

I must admit I have not built any of the Gen2 LT1 motors! That said, and I know it’s easy for me to say since I would have no vested interest, but I would still try one of the following two methods!

First of all the copper rtv to me makes no sense! This is typically used for high temps like exhaust manifolds, cats, etc! I don’t know why they would want you to use that?

Ok, so you clearly have to make the call here because you have the most experience with doing the work and seeing the failure! First, the easiest way is to use Permatex Ultra synthetic it comes in a purple tube! It is for oil applications! The other is their Ultra black, also for oil applications! Both have temperature ratings of -65 to 500F. Where as the copper is rated for 700F, but if your intake sees 700F you have other problems to worry about! 
Part of the failure may be due to the 700F rating! To get to that temperature material must be incorporated into the chemical composition that to some degree actually compromise the integrity of the structure with respect to oil exposer!
If you are going to pull and clean the manifold & the area of the block & heads that needs resealed, I would suggest this! Clean everything, reinstall the intake to head gaskets? Place the intake in place with no rtv, tighten the bolts just enough to make snug contact, no torque! Take feeler gages and measure the gap at manifold and block sealing surface areas! If it is more than .010 get back to me and let me know! If that is the case you might try something else I have in mind!

 

EFC039A5-54E3-4BD9-81E5-B9853C734699.jpeg

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4 hours ago, TWO LANE BLACK TOP said:

Last indian..

Thanks for the response...

The Gen2 LT 1 engine block and intake manifold are of a different design from the old school small blocks and instead of having the traditional cork/neoprene gaskets across the front/rear of the block...Between the cylinder heads...The Gen2  block and the bottom of the intake manifold are machined flat and fit tightly together with zero clearance between them and they are sealed with a copper type Rtv sealant...The only gaskets are the ones that seal the cylinder head intake ports and the manifold...Unlike the traditional small block No water flows thru the intake manifold..Instead there is a pipe that connects the Cylinder heads together for the coolant flow on the rear of the engine...(The engine has a reverse flow cooling system) with the water pump driven off the camshaft...

So I guess what I'm asking is..Is there maybe some kind of a nuclear space age super sealant RTV that will last for millions of heat cycles...and cope with the different expansion/contraction rates of the cast iron block and the Aluminum intake manifold....(Which is the point where the reoccuring leaks are happening)   That is commercially available...?? 

Just watched Freiberger rebuild one yesterday on Motortrend.  He only used RTV and was not copper.  BUT ....  His engines usually last the duration of his 1 hr show.:rofl:

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Two Lane, another RTV consideration would be to use Permatex Ultra Copper High Temp Silicone RTV. If for some reason, copper is needed as a barrier between the two dissimilar metals of the iron block and aluminum intake, this is another alternative.

image.thumb.png.b64b68075855efab232c10c5b11e471b.png

I've also heard of guys having sludge build up in the PCV system when they develop this leak on the LT1/LT4 engine. So if you remove the manifold, take the time to check out the entire PVC system for build up. If the PCV system has failed, you might have too much internal pressure blowing out the place of least resistance, the silicone seal.

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4 hours ago, Frosty said:

I've also heard of guys having sludge build up in the PCV system when they develop this leak on the LT1/LT4 engine. So if you remove the manifold, take the time to check out the entire PVC system for build up. If the PCV system has failed, you might have too much internal pressure blowing out the place of least resistance, the silicone seal.

yes, Two lane, frostys thought was what i was thinking too!, maybe its a back pressure issue thats helping the leak🙄

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17 hours ago, Frosty said:

Two Lane, another RTV consideration would be to use Permatex Ultra Copper High Temp Silicone RTV. If for some reason, copper is needed as a barrier between the two dissimilar metals of the iron block and aluminum intake, this is another alternative.

image.thumb.png.b64b68075855efab232c10c5b11e471b.png

I've also heard of guys having sludge build up in the PCV system when they develop this leak on the LT1/LT4 engine. So if you remove the manifold, take the time to check out the entire PVC system for build up. If the PCV system has failed, you might have too much internal pressure blowing out the place of least resistance, the silicone seal.

I believe this is the product Two Lane is using! And if you look at the picture you posted it is clearly listed as exhaust and 700 degrees F! Thus why I’m saying, I don’t really believe that is the right product for the application! That type of sealant usually does not have the proper composition for flexibility, ductility, shear strength or adhesion! It is usually has a composition more so for expansion, contraction. And while I know they say it’s oil resistant, I believe that is more from a exhaust oil perspective, not an engine oil bathing perspective! Otherwise why would you make any of the other products? You would JustA need one! Right?

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19 hours ago, Last Indian said:

I believe this is the product Two Lane is using! And if you look at the picture you posted it is clearly listed as exhaust and 700 degrees F! Thus why I’m saying, I don’t really believe that is the right product for the application! That type of sealant usually does not have the proper composition for flexibility, ductility, shear strength or adhesion! It is usually has a composition more so for expansion, contraction. And while I know they say it’s oil resistant, I believe that is more from a exhaust oil perspective, not an engine oil bathing perspective! Otherwise why would you make any of the other products? You would JustA need one! Right?

I don't disagree with you Last Indian. My first inclination would be to use a high RTV without the copper too. However, if GM spec'd an RTV with copper originally for these engines, I'm sure they had a reason. However, that reason alludes me.

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3 hours ago, Frosty said:

I don't disagree with you Last Indian. My first inclination would be to use a high RTV without the copper too. However, if GM spec'd an RTV with copper originally for these engines, I'm sure they had a reason. However, that reason alludes me.

Frosty, I understand that, and this is just my opinion, but I don’t believe GM says to use the copper! But if they do, I can only say they also say to use Dex-cool! And that crap is the worst s"?!t on the market! You might as well pour acid in your engine! While I never have built any of the LT1’s I have had a lot of interaction with the guys who were building them for our engine lab! They always used the red RTV! These engines ran hundreds of hours under some of the severest conditions! 
The one thing I remember they would tell me they always did was to put a blob of rtv in each corner at the cylinder head! Then run a bead on the rail! Also it was imperative that both the manifold & rail of the block be very very clean! I.E. all RTV removed, cleaned with brown scotchbrite & then wiped with an aggressive solvent like a carb cleaner!

below the first one is using the red RTV! The bottom pic is using a white, which I’m not familiar with, but it’s off of a Hot Rod build article! 

C03C311E-6040-406B-8380-26474ABAC886.jpeg

C2023466-4B07-4303-B77F-05CA55F47A0D.jpeg

Edited by Last Indian
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Back in the day..When these cars were new...There were alot of warranty claims for the oil leaking at the front and rear (mostly at the rear) of the intake manifolds...It is a very common problem...With these engines to the point that it was just a matter time before they all started leaking..They were only used for five years 92..96 Corvette...93..97 for the F bodies..Although they were used in various full size Buicks...Oldsmobiles..Chevies and certain Cadillacs during that time period.. But without the Aluminum cylinder heads...GM put out A TSB..That said to use the copper sealant  (shown in Frosty's pic) that instead of what had been originally used at the factory.. GM never really worked out the issue or made any design changes throughout the production run to address the issue...I think their reasoning for that was....They were coming out with LS series engines anyway and focused their attention on that..Instead of the soon to be obsolete Gen2 lt1/LT4 engines...personally I think the main design issue is the difference of the expansion rates of the Cast iron block and the Aluminum Intake manifold... GM Rather than machining a groove across the top of the the sealing surfaces of the block with a corresponding groove on the sealing surface on the bottom of the intake manifold...To put a flat O ring type gasket between the two...Just blew it off and moved on to other things....There is really no internal pressure in the valley under the intake..Unless the PVC system is clogged as Frosty pointed out...I will definitely look at that.... and address any issue that May be present...If I ever pull my engine or ever redo another one I will use a ball type end mill... And cut a shallow groove in both the intake and the block and take some of the material and instead of gluing it together at ends to form an O ring..I will just take a piece and lay it flat in the groove and sandwich it between the manifold and the block along with a coating of RTV...(I think that would be  permanent fix..??) But in the meantime I will remove the intake and  just use RTV.. If there is any commercially available RTV that will better cope with the different expansion rates between the dissimilar metals I Will definitely give it try...

Thanks....

Edited by TWO LANE BLACK TOP
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48 minutes ago, Last Indian said:

Frosty, I understand that, and this is just my opinion, but I don’t believe GM says to use the copper! But if they do, I can only say they also say to use Dex-cool! And that crap is the worst s"?!t on the market! You might as well pour acid in your engine! While I never have built any of the LT1’s I have had a lot of interaction with the guys who were building them for our engine lab! They always used the red RTV! These engines ran hundreds of hours under some of the severest conditions! 
The one thing I remember they would tell me they always did was to put a blob of rtv in each corner at the cylinder head! Then run a bead on the rail! Also it was imperative that both the manifold & rail of the block be very very clean! I.E. all RTV removed, cleaned with brown scotchbrite & then wiped with an aggressive solvent like a carb cleaner!

below the first one is using the red RTV! The bottom pic is using a white, which I’m not familiar with, but it’s off of a Hot Rod build article! 

C03C311E-6040-406B-8380-26474ABAC886.jpeg

C2023466-4B07-4303-B77F-05CA55F47A0D.jpeg

The day the new car warranty expired..First thing I did was Get Rid of the DEX-cool...Have seen several GM engines with the Aluminum cylinder heads/blocks...Heater cores.... Pretty much internally destroyed because of it...

Edited by TWO LANE BLACK TOP
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I just read today that a federal judge denied a request to make a 47-state class action suit into a single national class action suit against GM for DEX-Cool. He said it would be too complicated. So litigants have to either do state-by-state class action suits, or sue GM individually for damage caused by DEX-Cool.

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3 hours ago, TWO LANE BLACK TOP said:

Back in the day..When these cars were new...There were alot of warranty claims for the oil leaking at the front and rear (mostly at the rear) of the intake manifolds...It is a very common problem...With these engines to the point that it was just a matter time before they all started leaking..They were only used for five years 92..96 Corvette...93..97 for the F bodies..Although they were used in various full size Buicks...Oldsmobiles..Chevies and certain Cadillacs during that time period.. But without the Aluminum cylinder heads...GM put out A TSB..That said to use the copper sealant  (shown in Frosty's pic) that instead of what had been originally used at the factory.. GM never really worked out the issue or made any design changes throughout the production run to address the issue...I think their reasoning for that was....They were coming out with LS series engines anyway and focused their attention on that..Instead of the soon to be obsolete Gen2 lt1/LT4 engines...personally I think the main design issue is the difference of the expansion rates of the Cast iron block and the Aluminum Intake manifold... GM Rather than machining a groove across the top of the the sealing surfaces of the block with a corresponding groove on the sealing surface on the bottom of the intake manifold...To put a flat O ring type gasket between the two...Just blew it off and moved on to other things....There is really no internal pressure in the valley under the intake..Unless the PVC system is clogged as Frosty pointed out...I will definitely look at that.... and address any issue that May be present...If I ever pull my engine or ever redo another one I will use a ball type end mill... And cut a shallow groove in both the intake and the block and take some of the material and instead of gluing it together at ends to form an O ring..I will just take a piece and lay it flat in the groove and sandwich it between the manifold and the block along with a coating of RTV...(I think that would be  permanent fix..??) But in the meantime I will remove the intake and  just use RTV.. If there is any commercially available RTV that will better cope with the different expansion rates between the dissimilar metals I Will definitely give it try...

Thanks....

That’s a good point about the expansion rate! Quite often those are overlooked issues by manufacturers! I have seen that many times in my working career. 
So that prompted me to look at the MSDS sheets! Interesting enough the difference between the copper, black, red, blue & gray is enough to possibly make a difference in sealing! 

The red is the softest shore A 20, copper 26, black 30, blue 30 & gray 30-40! The elongation was close to the same for all except the gray, it was much lower! The shear strength was the lowest on the copper and the highest on the gray! 
So what does that mean? I’m not 100% sure because I don’t know the failure mechanism for sure! But if thermal expansion is part of the equation, which in turn creates the possibility of vibration? Than the red or the gray jump to the top of my list! Why? Well a softer durometer material with a ok elongation number might survive those demands! Still a harder durometer with a better shear strength might be tough enough to withstand both demands. 
But if it were me I would put my money on the red RTV!

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Two Lane, I'm still looking for more information but I read somewhere that GM developed a new (improved?) gaskets for the LT1s because of this oil leak. Not sure if this new gasket is the standard go-to gasket at over-the-parts-counter anymore, but I thought I'd mention it. This might have a groove in them.

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Thanks Frosty..

Seems Like I remember reading about the Impvoved gaskets too...I'm 95% sure that those are the ones that are sold new Nowadays.....

On 2/1/2021 at 9:54 PM, Frosty said:

Two Lane, I'm still looking for more information but I read somewhere that GM developed a new (improved?) gaskets for the LT1s because of this oil leak. Not sure if this new gasket is the standard go-to gasket at over-the-parts-counter anymore, but I thought I'd mention it. This might have a groove in them.

Will be doing the work starting in the next few days....When I Have a couple of uninterrupted days..Will also Replace the plugs and wires (Has never done) even though car still runs great...Just hoping I don't have any issues removing the original Spark plugs from the Aluminum cylinder heads..After 20 plus years...and 100,000 miles..

Any input on removing the plugs from the Aluminum heads would also be welcomed....All the spark plugs are pretty much only accessible from under the car and they're still a pain in ass to see/get to...Combined with fact that my hands don't work as well as they once did. (Getting old sucks).....If the engine was out of the car I wouldn't really be worried about it...

Edited by TWO LANE BLACK TOP
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I’ve heard of guys cutting down their spark plug sockets by 1/2 inch in order to get the socket on the hard to reach plugs.

Have lots of swivel head wrenches and sockets of various lengths in order to get at the spark plug socket.

I’ve  heard that guys with long tube headers have to remove the starter to get to #5 and #7, not sure if that is true.

Try not to push on the Optispark to hard especially if it is a working original like mine is.

Put anti seize compound on the threads of the new plugs, and a dab of dielectric grease on the boots.

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Thanks for the input...

My main concern is taking the plugs out of the Aluminum heads after 20 plus years...Without the threads in the heads coming out with the spark plugs...

Have seen lots of them that were seized through the years...When they finally came out the threads in the heads were galled/damaged....And required the spark plug holes to be helicoiled... Which is almost impossible to do correctly without removing the heads from the car due to the tight confines...Also by the same token have also removed them from Aluminum heads with absolutely no issues at all if the engine was still hot at the time of removal (although that is no guarantee they will come out with no issues) plus I do NOT want to be forced to repair damaged threads....So I figure it's pretty much luck of the draw as to which ones come out easy wth no thread damage as opposed to having to fight with them and still wind up with damaged threads....Guess I'm probably being paranoid about changing them...And I'm not looking forward to doing it....

 

Edited by TWO LANE BLACK TOP
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