Packard Forum Index » Post-War (1946-54)

Hi guys,
What’s the drawbacks if any to using 110 octane leaded fuel to blend with nonalcoholic gasoline in my 49’ std. 8 engine? Also if anyone is doing this already, would you share your mix ratio. I can get 5 gallons of SUNOCO 110 leaded for $73.009.
I value your opinion, as I think my valves would just love a little shot of lead!😀

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Leaded fuel won't hurt anything as long as you avoid drinking or bathing in it. As for benefits, I don't think you'd see any unless you habitually drive your car very hard.
There are lead substitute products sold that purport to protect valves from damage related to non-leaded fuel.

Marvel Mystery oil is much more economical than AV gas and probably of more benefit when used as a fuel additive per directions. It can provide some valve stem and upper cylinder lubrication and might help prevent "valve recession" in an engine that is run hard. AV gas is high quality and ethanol-free. AV gas might resist hot weather vapor lock better than today's pump gas. High octane fuel is not needed in flathead Packards. 87 is plenty unless you are pulling a trailer across Death Valley.

If you can afford the AV gas, 25% is probably plenty if added to non-ethanol gas. Any benefits of leaded fuel could probably be realized by blending 25% Avgas to every other tankful of ethanol-free non leaded. Concerning octane, as I understand it, adding a small amount of lead additive to non-lead raises octane substantially. Higher concentrations provide diminishing effects. Exactly how it affects non-lead that is already fairly high in octane may be different.

Thanks, I know that Tetraethyl works for the valves as history shows, but not so sure about the aftermarket products. I guess the vintage cars can legally cruise on leaded gas without any DOT repercussions……🤔

Thanks for the info, I guess the engine is running so sweet at 73, I want to feed it right, so she’ll last a looooooonng time!😊

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Sorry, what’s AV gas?

And what if I had the valve seats hardened? Do I still need to put lead substitute in once in awhile?

I believe AV gas refers to aviation fuel. It is used in aircraft engines requiring a higher octane rating with anti-knock properties, in higher compression engines, also used as a racing fuel for the same reason. Also aircraft flying at altitude may rely on a air compressor or supercharger of some sort, to keep the air flowing at pressures equal to atmospheres at or near sea level, to maintain adequate performance.
During WW2, Packard was really good building these engines.

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You don't need lead any any Packard straight eight motor. Period.

They are Low compression, low value spring pressures motors. It's a non-issue with these motors and how they are driven.

I've been driving with 87 unleaded for years, as most of us have been.

Big Kev is right as rain. And this topic is old news, "exhausted."

Tens of millions of cars in the eastern and midwestern US ran just fine hundreds of millions of miles for half a century on Amoco gasoline, which was always unleaded.

For belt and suspenders, use Red Line Lead Substitute, if concerned, which uses benign sodium as the dissimilar metal protecting from the nanosecond micro weld of valve upon seat. Potassium was tried in Europe, but leaves deposits, as did tetraethyl lead, vile ones, if you've ever examined the thick, deep, toxic goop on the bottom of the oilpan of an old original, never overhauled engine.

Lead causes brain damage in children, senility in adults. Children in schools near busy highways and streets tested lower academically than those afar. Someone adopting the appellation "Doc" might appreciate this.

Interesting priorities in some alleged "car guys." Sometimes it's good to venture out of the garage, see beyond our own hood ornaments.

Marvel Mystery Oil is a good product, protects valve stems and the upper wear zone of engines, including piston rings, but has no effect one way or the other on valve seats.

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Microwelding/valve recession only occurs in higher compression, higher output engines running under heavy load.
It's never been an issue with cars built prior to about 1956, and even those will have no issues if not driven hard, provided the cooling system is in good order, wear is within reason, and the valves are seating correctly with proper valve lash.


Before about 1955, lead levels were low even in "Ethyl" gasoline. Most pre war gasoline had very little lead additive, if any.

All that said, Av gas is fine for old cars, if you can afford it. It's high quality fuel, being stable and free of gum and ethanol.The lower octane versions of AV gas would probably be the best choice. The lead content will do no harm, except perhaps to the exhaust system. Some sources claim that leaded fuel promotes exhaust system decay, especially in lightly-used cars.

I' familiar with the gray goo in 1960s oil pans. I never heard of it being a problem, and it is probably evidence of inadequate oil changes. Gray goo and a light deposit of mahogany colored varnish were often found in older engines of that era.

The next best thing to Avgas would be "Tier 1" pump gas. It's supposed to be more stable than "off brand" gasoline.

Honestly, the only thing i miss lead in is red lead roof paint. As has been said, why bother with these anvil engines we drive? I'd worry about avgas in my hi-power hot rod with the ultra high compression modern engine - the one I don't have - yet. I run ethanol-free fuel every chance I get in the Packard and the motorcycles. They're installing a fuel station not far from the house in the hinterlands that'll carry booze free gas as a regular thing - 2 octanes, too. Back East, I buy gas at the busy by-the-interstate station because it cycles a lot of product and likely collects little water.


I'd concern myself more with boozy gas than lead any day.