LT4 Engine Oil Drain Plug
This is my first time changing the oil myself since I acquired this car. When I removed the oil drain plug bolt I noticed that it did not have any kind of gasket or seal. Should there be one? 
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'69 Blue/Blue L36 Vert w/ 4-Spd
'73 Blue/Blue L48 Coupe w/ 4-Spd
'96 Red/Black LT-4 Convertible
"Drive it like you stole it" -
Re: LT4 Engine Oil Drain Plug
Hi Floyd !
I've looked at a million of these during services, but now can't remember since you've asked. I'm almost sure there is a nylon washer on these. You sure there is not one under the shoulder of the plug ?Last edited by Tom H.; November 29, 2009, 05:38 PM.Tom Hendricks
Proud Member NCRS #23758
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'69 Blue/Blue L36 Vert w/ 4-Spd
'73 Blue/Blue L48 Coupe w/ 4-Spd
'96 Red/Black LT-4 Convertible
"Drive it like you stole it"Comment
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Re: LT4 Engine Oil Drain Plug
Floyd-----
Check your oil drain plug CAREFULLY. Note if it has an INTEGRAL elastomer seal on the flange area. It's easy to check but not so easy to SEE. Just press on the flange surface with your fingernail to see if it's "rubbery". If it is, this is drain plug that does not use a separate seal. And, you definitely DON'T want to add one. This integral seal plug seals FAR better than any previous plug + separate seal design. And, I mean FAR BETTER.
So, for those of you that might be wondering, why not convert small blocks with the earlier style plug to the later, integral seal design plug? Well, earlier pans use an SAE thread. The 1996 pans changed to a metric thread for the oil drain plug. So, the plugs are not interchangeable. I don't know of an integral seal style plug available from GM for SAE thread. There may be one now, though.
Attached is a photo of the integral seal design plug.In Appreciation of John HinckleyComment
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Re: LT4 Engine Oil Drain Plug
Bill-----
That nylon gasket may be what's there now, but I don't think it was always there. Has the car ever been to a "quick lube" sort of place for an oil change? If so, they probably replaced it.
I believe the nylon gasket was last used for the 1987 model year, if it was even used that late. The gasket used since then is a "composition"-type gasket composed of what I believe is a tin frame with a bonded fluroelastomer seal. It's GM #14090908 and it seals better than a nylon gasket (but nowhere near as good as the integral seal-type plug).In Appreciation of John HinckleyComment
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Re: LT4 Engine Oil Drain Plug
I am the only person that has ever changed the oil on my original owner 96 LT4. It does not have a gasket. Completed another yearly oil/filter change Friday. I will check it on next years oil change for the integral seal. Do not remember seeing it when I was cleaning oil off the plug directly after removal.Last edited by Jim T.; November 30, 2009, 06:41 PM.Comment
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Re: LT4 Engine Oil Drain Plug
Jim------
Yes, check for it next time. However, if it does not have a gasket and never had one, it almost certainly has the integral seal. Without one or the other, you'd have a serious leak.
By the way, how well does what you have seal? Do you have any seepage, at all, around the filler plug?In Appreciation of John HinckleyComment
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Re: LT4 Engine Oil Drain Plug
Bill-----
Over the years, GM went through all sorts of different gaskets for the oil drain and never solved the "weepage" problem. Very early (1955 and prior) used a metal/asbestos composition gasket. Later came several different versions of the nylon gasket and these were used for over 30 years but NEVER sealed well, even if you replaced it every time you changed the oil.
Later, they tried a copper gasket, but it was gone almost as soon as it was introduced. Then, the 14090908 came along and it worked better than anything prior----not perfect but better than anything prior.
Finally, the plug with the integral seal. After over 50 years, they finally got it right.In Appreciation of John HinckleyComment
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Re: LT4 Engine Oil Drain Plug
Joe,
You have solved another mystery for me. My plug required a 15mm socket to remove it and it does indeed have the integrated rubber seal. But the seal has been "squashed" during the past 13 years so it was dripping oil: not a lot, but some. I haven't refilled the crankcase yet so I can stop by the dealer and get a new plug tomorrow.
Thanx,
-Floyd-'69 Blue/Blue L36 Vert w/ 4-Spd
'73 Blue/Blue L48 Coupe w/ 4-Spd
'96 Red/Black LT-4 Convertible
"Drive it like you stole it"Comment
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Re: LT4 Engine Oil Drain Plug
Jim------
The Monte Carlo will almost certainly have the metric plug with integral seal. If it's a 3.1 or 3.4 liter engine, those engines are all metric and should have the integral seal plug.
If it's a 3.8 liter, that engine had most of its core components SAE size right to the end of production. However, the peripherals (including things like the oil pan drain plug) were converted to metric a long time ago. It should use the same drain plug as the above-referenced engines.In Appreciation of John HinckleyComment
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Re: LT4 Engine Oil Drain Plug
Joe, for those that don't want to buy a plug each time the seal gets tired, that seal is replaceable...at least it is on my 2006 LS2.
The seal is not an circular section o-ring, but is like a square section ring gasket (similar to a water hose gasket) with a semi-circular o-ring section molded to one face as a contact surface. You dig the old seal out of the groove, and press the new seal into place, and it stays. I purchased a couple of those seals early, but they came in a plain plastic bag...no part number.
Your picture of the elastomer seal washer used on LT1s reminded me that my later 87 with aluminum heads had that type drain plug seal when I bought it. The car had been owned by a Corvette afficianado however; if the seal could be interchanged with the nylon washer, he could have made that change himself.Comment
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