will it make it run bad

 

Unless you have updated the valve seats to hardend seats, you could do some damage to the heads and valves. The purpose of lead in gasoline was as a lubricant. The hardend seats allows the use of non leaded gasoline.

 

they did sell lead additve have not looked lately for it or you could add like one gal to a tank full of gas of air plane gas 100LL it is called do not add alot it has stabilizers for thin air as it will over heat the valves & guides but a gal to a tank you should be ok

 

Another urban legend. Unless you are going to drive the bejabbers out of your E-Type, don't worry about it.

See:
The E-Type Forum - celebrating 50 years of the ultimate motoring icon :: View topic - Sintered valve seats & Unleaded

 

+1, the old myths just won't die...........

This one is false also. There's nothing in 100L that causes it to burn faster, slower, hotter, cooler, etc etc. than any other gas.

 

...the higher the octane the more even the burn.....if you are operating your Jag in a high temp environ and/or lots of stop/go traffic octane could make a difference.

 

Nobody mentioned 'octane'. The discussion was about leaded/unleaded.

 

it was implied in reference to aviation fuel....

 

What was implied was the presence of lead. Pump gas is more than adequate when it comes to octane levels.

Your understanding of how gasoline burns and it's relationship to octane levels is also incorrect. The topic has been beaten to death many times- let's not go through it again.

 

Okay Cliff Clavin....

 

Unleaded will not hurt the Jaguar unless you race it constantly. Average driving and running occasionally at speed will not hurt these cars. The seats are hardened as the earlier Jags were manufactured and raced before lead was introduced to gasoline. Then they pulled the lead out again and same old white gas with octane inducers and additives. Low octane kills quicker as it pings and destroys the aluminum head more than the seats. I have run an E with 200,000 miles on it with no signs of fuel related problems, as the owner uses premium fuel and runs it hard once a week.

 

My 74 XKE had 100,000 miles before the restoration. When the engine was taken apart, it was in great shape and the shop advised it could have gone another 100,000 miles. The car used leaded gas from 74 to 75, and than starting 76 it went to strictly unleaded as leaded was phased out in USA and Canada. I went through the OEM shop manual and it makes no reference to leaded or unleaded, just rating.

 

My machine shop, which is an older generation of operators, was welding a spacer ring on a transmission gear. First did not want to do the job because they thought it was on the gear itself. He said the English back then (40s thru the present ) know how to harden steel. One of the best places for hardening steel. Did the job on the ring and did not touch gear. Anyway the seats for the valves were hardened back in the XK production to cover the internal heat from racing, and the owner of the shop said most seats are replaced as a money thing. He will only replace seats if needed as the process of heating the head and chilling the seats is still a lengthy process and must be done correctly or you will have more problems. They used unleaded fuel in the 40s thru the 70s and was not a problem. Cheap fuel and pinging hurt it the most.