Gas with lead substitute

I drained the gas from my Allis Chalmers tractor the other day. Due to the tractor’s age, I use a lead substitute in the gas. It’s going to be a month or two before I can use the tractor again so I thought I’d put the gas in my Subaru. Is there any potential problem in using the gas with the lead substitute in my car (about 6 gal.)?


If it actually contains Lead then YES…there’s a problem using it. Lead will DESTROY a catalytic converter. Very costly.

Keep the gas in the tractor, but add a stabalizer.

Instead of a ‘lead substitute’, try Marvel mystery oil. Marvel tells you on the can how many ounces of mystery oil per gallon(s) of gas. I use Marvel in the fuel in my A.C. WD-45 tractor. When the fuel in the tractor is about a month old, I drain and filter it then throw that into my '71 Chevy van. No problems. Last van engine rebuild was done using unleaded valves and valve seats in the head. (L-250 6-cyl. w/ 130K on last rebuild). If you use a lead substitute, you will damage your catalytic converter. You could also try a product like ‘Stab-il’ (I think). That stuff acts to prolong the volatility of gas. Use that in the tractor and don’t worry about any kind of a lead substitute adversely affecting your Subaru. My A.C. happens to be a 1956 model. Those engines were designed to use as low as 75 octane fuel. So fairly fresh fuel with Stab-il should keep the gas fresh enough for the tractor for several months. Check the label on the Stab-il container for correct mix. Using both Stab-il and Marvel Mystery Oil, plus a bottle of ‘dry gas’ in the winter has not at all affected the old A.C. engine.

I agree with the answers you’ve seen but let me add: After you add the stabilizer, run the engine for awhile, well, at least long enough for the mixed fuel to run through the carb and fuel line so it will have used the ‘old’ gas up.

I do this with my snow blower (lawn tractor too) every spring and come winter, start ups are immediate and with no engine miss.

I seriously doubt that you will have a problem with your cat converter. The lead substitute that I used to buy at WM had no lead in it. Read the bottle; it should tell you if it is safe for a cat converter. Otherwise call the company or look a their web site.

Old gasoline engines don’t need lead or lead substitutes to keep them healthy. That’s “urban legend” stuff. Gasoline has a shelf life of at least 6 months and with “stabil” added, it will go a year or more…

Old gasoline engines don’t need lead or lead substitutes to keep them healthy. That’s “urban legend” stuff.

In 1975 when new cars had catalytic converters and required unleaded fuel, the engines started being built with hardened valves. The hardening was needed to compensate for the “lubricant/cushion” effect that the lead once provided.

I remember doing valve jobs on pre-1975 cars (without hardened valves) that used unleaded gas over a period of time. A common problem was a recession in the valve-seat contact area.

I do remember, however, hearing many people saying they used unleaded in pre-1975 cars with no ill effects. If someone knows why, I’d be interested.

It seems from what I have read on the internet on this topic, is that valve seat recession is a function of how hard the motor is required to work. Most motor vehicle engines are just loafing at 60 mph as only about 10 or so horsepower is needed to keep a car moving. A tractor engine, on the other hand might be required to work hard for plowing, for example. Pulling a wagon down a flat road would be easy going.

People with antique cars typically drive them gently for fear of breaking something that may be expensive to repair.

Valve recession can occur on any engine and many of those old cars hold up well because the cast iron used back then had a high nickel content. Since the seats were part of the cast cylinder head the nickel allowed them to stand the abuse.