Rebuilt flathead V8
Fleet Owner
Joined: Dec 2000
Posts: 25,431
Likes: 5,439
From: Central PA
I don't have a flathead. I have a 54 Yblock. Years ago (1990's) I used it but then did some research.
Most of the experts here say unless you are hauling loads daily or drag racing you don't need to use lead substitute. And of course the additive is not lead.
If your engine has recently been rebuilt I would think it got hardened seats.
And welcome to FTE the best Ford truck forum on the World wide Web.
Most of the experts here say unless you are hauling loads daily or drag racing you don't need to use lead substitute. And of course the additive is not lead.
If your engine has recently been rebuilt I would think it got hardened seats.
And welcome to FTE the best Ford truck forum on the World wide Web.
Fleet Mechanic
Joined: Aug 2019
Posts: 1,372
Likes: 421
From: Monmouth County, NJ
I’ve seen a lot of people, especially older people recommend using marvel’s mystery oil as an all around alternative to replacing the lubricity that they claim pump gas lacks today. I think running Stabil is probably even more important.
Lead Driver
Joined: Oct 1999
Posts: 6,783
Likes: 559
From: Kalispell, MT
No on lead substitutes. Originally designed in the 1920s for it's anti-knock properties, today there are safer ways to raise octane. I've never had issues with 87 regular gas.
I tried it 25 years ago but quit using it after doing some research.
Interesting side note - my dad owned a Sohio franchise around 1959/60. He often mused how gas companies charged more for gas when lead was added (ca. 1923) to it, and then in the 70s charged more for gas to "remove it".
I tried it 25 years ago but quit using it after doing some research.
Interesting side note - my dad owned a Sohio franchise around 1959/60. He often mused how gas companies charged more for gas when lead was added (ca. 1923) to it, and then in the 70s charged more for gas to "remove it".
Hotshot
Joined: Oct 2009
Posts: 16,205
Likes: 4,818
From: Burbank, WA
It seems the general consensus around here is that for general pleasure driving, needing lead or additives isn't a big deal. It's not likely you're going to drive it enough to ever wear it out cruising to Dairy Queen on Saturday nights. If your plan is to work it hard or go on a cross-country trip, that's another matter and it may be better to add hardened seats rather than trust some snake oil additive to protect you. But as they say, your mileage may vary. Welcome to the forum!
Fleet Owner
Joined: Jul 2004
Posts: 27,304
Likes: 1,062
From: NM
'51 and later flatheads didn't all have hardened seats. You might be able to tell by looking thru a spark plug hole with a borescope.
Trending Topics
Fleet Mechanic
Joined: Aug 2019
Posts: 1,372
Likes: 421
From: Monmouth County, NJ
hi Ross. I thought the OP was asking most likely about a rebuilt flathead as it’s in the title of his post? As there probably isn’t any original from the factory flatheads out there still running? We are most likely taking about a rebuilt one and they from what I understand almost invariably have hardened seat valves. However it’s interesting to learn that some came that way from the factory.
Concerning the lead substitute and the reason people use it, doesn’t it go just beyond hardened Seat valves? I thought it was claimed to be a lubricant as well. This is why people recommend using the marvels mystery oil? I have heard read a lot on forums to this effect although I don’t have any experience or opinions. I’m just curious to hear what you and others think.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
3 Best / Worst Features Of The 2025+ Ford Expedition
Brett Foote
10 Ways Ford is LOSING to the Competition
Joe Kucinski
Top 6 Best Deals Available on New Fords & Lincolns Right Now
Brett Foote
This Hennessey Takes the Expedition Tremor's Off-Roading Capability to the Next Level
Verdad Gallardo
Top 10 Fords at 2026 Carlisle Ford Nationals
Joe Kucinski
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
Parts Nerd Extraordinaire
Joined: Sep 2010
Posts: 4,396
Likes: 1,801
From: Western NY
Ford stopped the hardened valve seats and introduced rotating valve assemblies. Discussed here with Ford documents: https://www.ford-trucks.com/forums/1...l#post21747992
Thread
Thread Starter
Forum
Replies
Last Post
Tom
Y-Block V8 (239, 272, 292, 312, 317, 341, 368)
5
Aug 22, 2004 08:03 PM