Hi all,
I need some advice please - I have got a 1968 Jag 240 (Mk2 shape) and I don't know which octane fuel is best to use (Regular or Super)? I am not sure if the engine has been adapted for unleaded petrol so I recently added some lead replacement additive to the petrol and now my car smokes rather a lot. I don't know if it is because I put the additive in or not? Should I use any additive or should I run the car on straight unleaded fuel (Regular/Super).
Any advice greatly appreciated.
Many thanks,
Andy

 

This will be a looooong thread, but from the Colonies, my opinion,

I use our 98 RON in ALL my Jags, even the MK10, and NO additives at all.

The engine is fine, its a Jaguar, and one must have faith.

Our 98 probably converts to your Super, coz we got Standard which in known as 91RON.

That snake oil additives can cause smoke, so I would not worry too much, but do not add anymore, let it run its course.

 

Hi Grant,
Many thanks for your reply, which is duly noted. I will fill up my tank tomorrow with our (UK) Super petrol which is 98 RON and hope for the best!
Regards,
Andy J

 

Andy,

I forgot, it happens.

Drive it like ya stole it from time to time, that XK will run forever with that attitude.

 

Jaguar engines had hardened valve seats fitted from some time in the 60s, but before 1968, I think. This was because unleaded fuel was about to be forced through in California. I sold my Mark 2 in 1988 and can't remember what I put in, it was probably 4-Star ! I ran my 1980 XJ6 on unleaded 95 RON.

 

 

I forgot to mention my 1977 MG Midget 1500 (see the little yellow car behind he Jag), which definitely does NOT have hardened valve seats ! For this car, I add Castrol Valvemaster Plus to the fuel when I fill up. Valvemaster Plus is an octane booster and also lead substitute. I always full up with 95 RON petrol, not the 98 RON stuff. So far I have had no trouble with the car at all, it runs beautifully.

So, if you want to use 95 RON, and not alter the ignition timing, buy this stuff and add it in when you fill up. I am assuming your car is not a daily driver, and is only taken out for pleasure purposes like my Midget.

 

Octane level of a fuel and valve seat protection have no connection whatsoever.