Hi fellow xtypers! New to the forum and a new jag owner. Glad to have you all as a support. I am currently putting 89 octane in my car. Some are telling me I should be using 91. Thoughts or experiences with different octanes? It is running a bit rough. Also, anyone know where I can get the spring kit to attach the hood ornament? My car was missing it when I bought it but I was able to obtain one. Just don't know how to get it on the hood now. Thanks in advance

 

Hello and welcome. I have always put premium gas in mine. The one day i put regular in it... I had the infamous gearbox fault and it went into limp mode. I dont know if it was related but it never happens when i use premium

 

Ebay for hood ornament and sometimes using less than 91 causes the engine to knock and in some case, go into limp mode

 

Thanks, guys, for the octane information. What an education I am gaining from this forum. Am not thrilled, however, to find out that I have to start buying the $4/gal gas. (((( I researched "limp mode" and this is exactly what has been going on with my car. Check engine light has been coming on, riding really slowly, idling high etc. Thanks for the info on the hood ornament as well. Once she is "fully dressed" with her ornament I will post a pic. The guy I bought the car from also told me I should have a complete check of the car fluids that costs about $600. Is this something you think I should have done? Have a great weekend.

 

I have been using mid-grade (89) octane for two years and have never had a problem. No CEL, knocking, and she always runs smooth. I had a gearbox fault back when I first bought the car, but that was due to a wiring issue under the dash (a wire pinched by the tilt steering column).

I average about 26 MPG in my highway/city mix of driving, 57 miles round trip every day work commute.

 

I'd like to hear more about the supposed connection between low octane gas and limp mode.

 

If you plug in the mileage between 89 and 91 octaine, and factor in the cost...the difference in mileage is not anything to deal with. I get more MPG on 91, than on 89. Costs equate on all my cars, the Jag,and my Alfa Spyder. Try it. Also, the owners manual says 91, so I'd believe them. It makes a difference in the way you will drive...Also the additives in 91 are different (more) than in 89.

 

This is by and large not true- but even if it was the 'extra additives' are not required. Why would cars rated for lower octane gas run OK with less additives and not our cars? Engine deposits and buildup are not related to compression ratio or HP output.

 

the reason that our cars run better on higher octane is because that is the octane they are tuned for. I personally have never had the problem of my car riding rough with low octane, yet I know this is a common problem. The reason that this is a problem with jaguar engines is because jaguar engines run at a higher compression compared to other engines. That's one of the reasons that the x type is able to get around 240bhp out of a 3.0 compared to most other cars with a 3.0 that only get around 200. The level of the octane is the fuel's ability to withstand pre-ignition and heat. With that being said, 87 octane will combust earlier than 91 octane and cannot withstand as much compression and heat as the 91 octane. Again, because our engines squeeze so much power out of such little displacement, sometimes if we use 87 octane it will combust too soon and put our cars into limp mode. Yes, 91 octane is more expensive, and before I was educated on the matter, I too bought 87 octane. I hope I have been able to explain this well enough that others will also learn to step up and buy 91 octane.

 

I think you mean detonation, not pre-ignition- these are very different phenomena. Pre-ignition is not cured or affected in any way way by fuel octane levels, whereas detonation is.

All modern cars are equipped with knock sensors which will detect even slight detonation- far less than the driver could possibly be aware of- and retard the timing as required to eliminate the problem. This is a normal function of he car and will not set it into limp mode. If anything the car might seem down on power or get reduced fuel mileage but that's it.

 

+1 to disguay
I've been using 91+ since I got this car. The previous owner never used anything but 91+ as well.

 

Yes, you are correct. It will retard the timing in order to reduce the risk of preignition. I just described it a little bit different. The main point is that our cars must use 91 octane

 

Not pre-ignition, detonation.

 

I've been using 89(mid grade) when temps are consistently below 50deg. All other times it's 93(high grade). This per jaguar technician when I bought the car. It's worked out well for me.

 

Interesting and good to know

 

Ive only used 87 octane (2 years)now that ive had the car. never had any troubles with it. i do however put lucas fuel treatment in it every few months. plus i dont drive but 25miles a week or so in mine.

 

I only use 91 and sometimes treat it to 94

 

Here is what I tell folks who ask. If you run 87 and your happy with it run it. If you run 91 all the time your car becomes"octane hungry' and will ping if it don't get it then you have to use it always unless you clean it. Most newer cars have enough leeway built into the emission system to defer changes in altitude and octane which both figure into the equation. This is a general rule and you know about rules, And all gas stations are not equal to what they dispense state for state/country for country.I have ran 87 for 100k in the Jag. with no problems but have noticed when traveling there is a mileage change from state to state. This is true from when I was driving my Dodge Dart in 1970 to the 2010 Chev. HHR.(rented) especially in the mountains.

 

According to my Owners Handbook (2004 X-Type 2.5L LE Sports) it stipulates
Premium Unleaded Fuel.

According to our Shell Outlets here in Australia;

Standard Unleaded Petrol = 91 Octane
Premium Unleaded Petrol = 95 Octane
V-Power Unleaded Petrol = 98 Octane

Coles Express | Shell Fuels

I've always used 95 Octane - as recommended by Jaguar,
and Never had an issue to date.

Cheers,

 

Your 95 (RON) octane in Australia is equivalent to our 91 (RON+MON/2) in the USA.