# Older Cars & Leaded Gas **URL:** \ **Category:** Factual Questions\ **Created:** [April 2, 2000, 7:42pm UTC](https://boards.straightdope.com/t/older-cars-leaded-gas/9652 "2000-04-02T19:42:00Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Torgo](https://avatars.discourse-cdn.com/v4/letter/t/94ad74/32.png) [@Torgo](https://boards.straightdope.com/u/Torgo)\ **Post date:** [April 2, 2000, 7:42pm UTC](https://boards.straightdope.com/t/older-cars-leaded-gas/9652/1 "2000-04-02T19:42:00Z")
Do the majority of older cars (pre-1980) require leaded gasoline (or a lead additive) or can you go ahead and pump unleaded into the tank without fear of any consequences? * * * “My hovercraft is full of eels.” ---
**Author:** ![Scylla](https://avatars.discourse-cdn.com/v4/letter/s/a5b964/32.png) [@Scylla](https://boards.straightdope.com/u/Scylla)\ **Post date:** [April 2, 2000, 7:55pm UTC](https://boards.straightdope.com/t/older-cars-leaded-gas/9652/2 "2000-04-02T19:55:00Z")
They year is '73 or thereabouts, and you need to add a lead substitute ---
**Author:** ![billehunt](https://avatars.discourse-cdn.com/v4/letter/b/c37758/32.png) [@billehunt](https://boards.straightdope.com/u/billehunt)\ **Post date:** [April 2, 2000, 9:10pm UTC](https://boards.straightdope.com/t/older-cars-leaded-gas/9652/3 "2000-04-02T21:10:00Z")
I’ve got a 63 Corvair. For the last couple of years I’ve used the high octane stuff, and it runs fine. ---
**Author:** ![Scylla](https://avatars.discourse-cdn.com/v4/letter/s/a5b964/32.png) [@Scylla](https://boards.straightdope.com/u/Scylla)\ **Post date:** [April 2, 2000, 10:14pm UTC](https://boards.straightdope.com/t/older-cars-leaded-gas/9652/4 "2000-04-02T22:14:00Z")
Billehunt: (please, not again) Is it the original engine? has it been modified to accept unleaded? If not, the engine needs the lead or the substitute for lubrication. If you are not using it, you are damaging the engine. ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [April 2, 2000, 11:54pm UTC](https://boards.straightdope.com/t/older-cars-leaded-gas/9652/5 "2000-04-02T23:54:00Z")
Lawnmowers, old vw’s, etc do fine on unleaded. You don’t have to add lead substitute at all unless you go 60mph a lot. ---
**Author:** ![Joe\_Cool](https://avatars.discourse-cdn.com/v4/letter/j/ecb155/32.png) [@Joe\_Cool](https://boards.straightdope.com/u/Joe_Cool)\ **Post date:** [April 2, 2000, 11:57pm UTC](https://boards.straightdope.com/t/older-cars-leaded-gas/9652/6 "2000-04-02T23:57:00Z")
the lead cushions and lubricates the valves in older engines. If it doesn’t say “unleaded fuel only” and hasn’t been rebuilt with hardened valve seats, then you need to use a lead substitute. ---
**Author:** ![pmh](https://avatars.discourse-cdn.com/v4/letter/p/df705f/32.png) [@pmh](https://boards.straightdope.com/u/pmh)\ **Post date:** [April 3, 2000, 12:16am UTC](https://boards.straightdope.com/t/older-cars-leaded-gas/9652/7 "2000-04-03T00:16:00Z")
Yes, lead did help lubricate the valve guides and seats, and yes, running one of these older motors without leaded gas will cause those areas to wear faster, but an additive is not neccesary. It will take about 50k miles of normal driving to see any significant wear due to the lack of lead in the gas. At that time you can replace the guides and seats for far less than what you would have spent on additives. I would only recommend an additive if you car knocks with premium unleaded AND you have already tried all the normal tricks (re-curve the dist, thicker head gaskets, etc). ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [April 3, 2000, 3:02pm UTC](https://boards.straightdope.com/t/older-cars-leaded-gas/9652/8 "2000-04-03T15:02:00Z")
‘the lead cushions and lubricates the valves in older engines. If it doesn’t say “unleaded fuel only” and hasn’t been rebuilt with hardened valve seats, then you need to use a lead substitute.’ This is a common misperception & has been proven to not be the case by the biggest automotive people in the world. ---
**Author:** ![Centerline](https://avatars.discourse-cdn.com/v4/letter/c/94ad74/32.png) [@Centerline](https://boards.straightdope.com/u/Centerline)\ **Post date:** [April 3, 2000, 4:32pm UTC](https://boards.straightdope.com/t/older-cars-leaded-gas/9652/9 "2000-04-03T16:32:00Z")
As I recall, lead was added to gasoline as an Octane enhancer. I will try to get references when I have time. The biggest problem with unleaded was that the octane ratings were low. The main thing to do is to retard the engine timing so that the lower octane gas have time to complete is combustion before the piston hits TDC. The flame front is much slower. Otherwise severe knocking will occur. The same thing will happen if you put low octane gas into a high compression high performance engine. But because you retard the timing, an old engine will produce much less horsepower, but its workable.