Premium gas

My 2006 Jaguar says it needs premium gas— or at least the dealer does. I sometimes forget and it seems to run fine on regular. Am I hurting the car by not using premium? There are several other cars with same engine that do not use premium.

Yes, is says 91+ octane required, and it means it.

Several other cars that use the same engine? Please name them, I’d like to know about this (I’ll bet that Jaguar would too).

When it says it needs premium, it means you may (likely) loose power and may damage the engine if you don’t use premium. You also will likely get a little lower mileage, all things taken together means it is cheaper to use premium.

You should use premium gas. You will lose power and gas mileage without it.

this car was manufactured by Ford (owned Jaguar at that time)- same platform as Volvo, Ford and a Mazda- In Europe this exact car is often a Ford with slightly less fit and finish. The 3.5 engine is same as in a Taurus, Lincoln and Volvo- which makes the same horsepower with regular gas. I would be surprised if Jaguar (Ford) doesn’t know where they acquired their engines. New Jaguars are now a different consortium- and the X and S are dropped and no more 6 cylinder engines.

Yes, it’s a modified Ford Mondeo (prior version sold here as the Ford Contour). It has a 2.5 or 3.0 l engine, not the 3.5 l. What exactly does the manual (not the dealer) state? “Recommended” or “Required”?

Best case - the engine doesn’t put out as much power, and you lose some fuel economy.

Worst case - you get some premature detonation and damage the engine (gradually…takes some time, but it’s still not good.)

The octane rating determines how resistant the fuel is to detonating…lower octane fuels used in an engine designed for high octane fuel (anything with high compression ratios, like most sports cars) may be detonated by the heat and pressure of the engine rather than by the spark, which is bad for the engine.

Most new cars that use high octane fuel can adapt to low octane fuel, but at the cost of performance. That is probably what will happen if you don’t use premium.

Also, other cars with “the same engine” might not have EXACTLY the same engine. If you can’t find other more specific identifiers, look for the rated power output. If it’s different, the engines are probably related, but different.

If you can not detect any spark knock or detonation, you are not hurting anything…

Those aren’t the same engines. They are similar engines, and share a few parts. However, the controls are different, and that is what determines the octane that they need. Go back and do some better research on this.
I happen to have a couple of Lincoln LS’s. These are sister cars to the Jaguar S type. The engines in these cars use modified Jaguar engine blocks, but the top halves of the engines are different. Even if they weren’t the octane required can be changed just by minor changes in the engine programming.

I agree. Detonation is very obviously audible unless you have the radio turned up very loud. It is becoming a noise from the past that possibly few have heard. Cars since the 1990s have knock sensors on the engine block that hear detonation, spark knock, pinging or pre-ignition and will instruct the engine control computer to back off the ignition timing even with cars that can better use premium gasoline.

I have heard pinging for many years and many times, the first time when my Dad went around a corner in his 1937 Chevy in the late 1940s and accelerated in too low a gear on a hot day.

In 1957, Oldsmobile came out with the “J-2” Rocket engine. Three deuces, dual exhaust, 4-speed Hydramatic that would truly light 'em up if you punched it…Olds claimed 12 to 1 compression and if you strayed from the “high-test” gas nozzle, everyone on the block could hear that poor engine rattle. High Test back then was 100 octane…

So when I see these “Octane” threads, you’ll have to forgive me if I find them somewhat amusing, all this hand wringing about a little occasional ping…

Those kept the old Sunoco pump in business!

Every case is not the same and if the fuel mileage stays about the same along with the most important factor, no pinging, I wouldn’t have a problem running lower octane at all.

Until I wrecked my Lincoln Mark a few months back, that car (uses 91) got nothing but a steady diet of 87 and on repeated trips to the CO mountains it got 85 with never a hiccup, loss of fuel mileage, or one ping taking place. After about 150k miles of 87 only I decided that it wasn’t a problem.

Also, repeated inspections of spark plugs showed zero problems and the same applies to my “new” used Lincoln Mark. Not a peep out of it under any conditions.

And as per the usual, when you refer to talking to the “dealer” this probably means a conversation with a service writer or service manager. Very, very few of these guys have any mechanical abilities and simply recite what they’ve heard even if it includes old wives tales.

Until I wrecked my Lincoln Mark a few months back, that car (uses 91) got nothing but a steady diet of 87 and on repeated trips to the CO mountains it got 85 with never a hiccup, loss of fuel mileage,

If it got nothing but low octane fuel, how would you know if the fuel economy didn’t decline?

I bought this car sight unseen over the internet- so no manual. Am scrounging for one. Yes the local Jaguar dealer was very nice service manager, but strangely inept. Again pleasant and the car has 60,000 miles remaining on warranty and 3 more years, so no cost involved, but the problems did not actually get fixed either. I would say recommended is more in line with what he said, but online says to use premium. On the filler says 90 octane— our midrange in 89, and high test 92. I have run a tank of 87 and a tank of 92, and since I drive interstate on cruise control mostly, I could tell no difference in sound. Unfortunately the (unsuccessful) repair was to the RADIO- which gets no stations greater than 30 miles from a large metro area— I have great opportunity to hear the engine- the HVAC is wonderfully quiet as are the tires and road sounds. I drove about 380 miles on about 14.5 gallons each way- which is kind of in the range I expected. The rated output of power from the related engines is identical best I can tell.

Because on several road trips to TX and CO I used several tanks of 91 for test purposes. The fuel economy is the same no matter if it’s 91 or 87 and as a matter of fact, when traveling the mountains of CO and using 85 the economy actually improved to about 28 to 28.5 from the normal 27 MPG.

The reasons I don’t worry?
No pinging, no power loss, and no loss of fuel mileage.
Examination of the spark plugs (which I do every 15k and replace them every 30k) shows absolutely nothing going on inside the engine that would cause even one second of alarm.

And something to keep in mind is that when pinging does occur that does not automatically mean the octane rating of the gas is not high enough. It’s often due to an EGR system fault. Fix the EGR problem and any pinging will likely go away.

Well, I’d say your car is a good candidate for regular. I did the same thing with my '96 Lexus ES300. Premium is ‘recommended’ in the manual for ‘optimum performance’, but it’s the exact same engine specs as the Camry V6. I switched to regular the year after I bought it, and have noticed no problems and no decrease in performance or milage.

Hopefully you’ll get your hands on an owner’s manual and verify - “required” and “recommended” do mean different things.

But think about this - most people who ask this question are looking to save money at the pump by not paying extra for premium. If you actually sit down and do the math you will probably find that the extra money isn’t nearly what you think. And if you weigh it against possible engine damage it can sometimes be “penny wise and pound foolish” - as they say.