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Unleaded gas in old cars

I am looking to buy an older luxury car (1960’s or early 1970’s). Will I have any problems burning unleaded gas in this car or is there anything that I will have to do so that the car will run smooth with no pinging, knocking, etc. ?

An early 60’s vehicle won’t have hardened valves or valve seats. So with the lack of lead in the gas there will be no lubrication for these parts. So you could end up with valve recession. By the 70’s however, engine manufacturers were installing hardened valves and valve seats so they could tolerate unleaded fuel without valve damage.


I believe that auto part stores sell a additive for using unleaded gas in older cars.

Are there any additives that can prevent or reduce valve recession?

I think that’s been banned from stores now.

In my old vehicles, '71 Chevy Van, 250 c.i. in-line 6 and my '56 Allis Chalmers farm tractor 4-banger engine, I use Marvel Mystery Oil. It comes in 1 gallon plastic jugs now. Follow the instructions on the jug. It’s about 2 ounces of MMO per 5 gallons of gas. In the van, I have an old used plastic bottle that formerly had chalk line chalk in it. I used a magic marker to mark lines on the bottle so the bottle has exactly 1/3 bottle marks. When filling up, I simply pop off the cap and pour in 1/3 bottle of MMO then pump the gas. MMO works like lead used to without the air pollution qualities of leaded gas. It acts as an upper cylinder lubricant and acts as a “cushion” for the valves like leaded gas used to do. Van has 115,000 miles on a rebuilt engine. No valve issues. Tractor is a '56 so I have no idea how many hours are on it. No valve issues. As I get my gas for the tractor via a 16 gallon steel drum that I fill up at the gas station, I place the appropriate 6 ounces of MMO into the steel drum at home prior to going to the gas stop. I use this gas out of the drum for my log splitter engine, chain saw and weed whacker, also. Log splitter is a 4-stroke. The two-stroke engine gas is mixed with the appropriate type and amount of 2-stroke engine oil in a separate small container. Works for me! No valve issues on any of this stuff.

I’ve run a lot of old cars on regular gas with no problem. Although the oldest one I have is a Buick with aluminum heads, so it’s not an issue with that one. And I suppose the other one from the 60’s is a VW with an all-aluminum engine. However, I have owned a few pre-74 pickups with iron engines and they did just fine with no lead additives.

I’d talk to the owner about it-- chances are that most cars from that vintage that have been on the road for any length of time since the carter administration have had their valves redone to be compatible with unleaded gas. Unless the owner has been driving it extremely few miles or personally putting in lead additive since the mid-70’s, I wouldn’t worry about it.

Check at a WM store in the auto parts section for a quart container of lead substitute. The container has a built-in measuring section. It does not have lead in it and last I checked, WM still had it. If you drive in an easy manner, it is likely that your engine will not have valve recession but the lead substitute is cheap insurance.

When I used to work at a gas station a few years ago, a lady (I think it was a lady… couldn’t quite be sure, though) came in with an old Porsche 911. After filling the tank, she added a bottle of liquid with lead or a substitute to the tank. So you can certainly get the additive, but you might have to look around a bit - it won’t be all that common.

I presume you will be using this as a show car. If you go easy on the throttle, no problems. I ran my '67 Cougar on regular unleaded gas during the 1990’s as a daily driver for over 80K miles on a rebuilt 289 with OEM non-hardened valve seats with no ill affects. The engine was still running strong before being T-boned by an idiot that blew through a stop sign.