Why Does Oil Drain Plug Keep Loosening Up?
Thread Starter
Burning Brakes
Joined: Oct 2009
Posts: 1,065
Likes: 56
Why Does Oil Drain Plug Keep Loosening Up?
'70 C3 350/300 w/48K original miles. Stock everything.
Cleaning underneath today, I saw a drip of oil hanging off the oil pan drain plug and decided to snug it up while I was there.
I was surprised that the drain plug was just a little more than finger tight. It's the original drain plug with new nylon washer.
I was the last person to change the oil sometime last year. I always tighten by feel to what I imaging would be about 25 ftlbs.
What can I do to not have the plug loosen up in the future?
Thanks
Cleaning underneath today, I saw a drip of oil hanging off the oil pan drain plug and decided to snug it up while I was there.
I was surprised that the drain plug was just a little more than finger tight. It's the original drain plug with new nylon washer.
I was the last person to change the oil sometime last year. I always tighten by feel to what I imaging would be about 25 ftlbs.
What can I do to not have the plug loosen up in the future?
Thanks
Safety Car
Joined: Dec 2012
Posts: 3,781
Likes: 1,686
From: Summerville SC
Your finger needs to be recalibrated. I always would use the FEEL method but in your case( since you have a new washer, that will compress the first few times you tighten it) I would get a torque wrench on it. Just so you know for sure what that FEEL is. 
Thread Starter
Burning Brakes
Joined: Oct 2009
Posts: 1,065
Likes: 56
Box wrench only.
Thanks
Thread Starter
Burning Brakes
Joined: Oct 2009
Posts: 1,065
Likes: 56
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 8,998
Likes: 4,152
From: US-PNW
Might you be able to snap a clear pic of the drain bolt in the pan? I'm imagining a GM bolt and pan, but that may not be what you have.
Thread Starter
Burning Brakes
Joined: Oct 2009
Posts: 1,065
Likes: 56
I think kanvasman has a good comment that the new gasket may need to be seated better — and yes, you should have a plastic washer there. Make sure there are no metal burrs on the sealing surface of the pan or the underside of the bolt's head that can nick the plastic washer and allow oil to seep past.
Might you be able to snap a clear pic of the drain bolt in the pan? I'm imagining a GM bolt and pan, but that may not be what you have.
Might you be able to snap a clear pic of the drain bolt in the pan? I'm imagining a GM bolt and pan, but that may not be what you have.
Correct Repro nylon washer.
Thanks
Melting Slicks
Joined: Nov 2006
Posts: 3,380
Likes: 1,799
From: Apple Valley, MN
You just need to apply German Torque - Guten Tight.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
Drifting
Joined: Jun 2025
Posts: 1,611
Likes: 567
Race Director
Joined: Nov 2006
Posts: 13,146
Likes: 7,758
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
Just what I was thinking. Nylon washers get soft with heat.
I personally would be running a copper washer on that drain bolt.
I personally would be running a copper washer on that drain bolt.
Drifting
Joined: Jun 2025
Posts: 1,611
Likes: 567
If car Not being judged; consider a sturdy, competition-grade, US-made pan that have some oil/windage-control improvements over OE.
Either Canton, Champ or Milodon brands.
* But do Not settle on a "Drag race" pan; those typically hang down too low for an already low-slung Corvette.
Either Canton, Champ or Milodon brands.
* But do Not settle on a "Drag race" pan; those typically hang down too low for an already low-slung Corvette.
Last edited by Rebelyell; May 9, 2026 at 11:38 AM.
Melting Slicks
Joined: Apr 2023
Posts: 2,663
Likes: 1,595
From: Poplar Bluff MO
With the plug screwed part way in does the plug wiggle a lot? This might indicate striped threads.
Edit: I've never had a drain plug come loose so there must be something wrong with either the plug or the threads in the pan.
JT
Edit: I've never had a drain plug come loose so there must be something wrong with either the plug or the threads in the pan.
JT
Last edited by jthornton; Yesterday at 07:10 AM.
Safety Car
Joined: May 2001
Posts: 4,737
Likes: 1,638
From: Fairfax Virginia
After dozens of oil changes is it possible the threads on the pan's drain bolt are just a bit looser than they were meant to be in the beginning? I would try a new oil pan bolt with a new sealing washer before replacing the entire oil pan.
Race Director
Joined: May 2006
Posts: 18,653
Likes: 2,557