Am I wasting money by putting optimax in my XJR
Discussion
Unless your car actually retunes itself to the higher octane you are indeed wasting your money.
I dont know if the Jag ECU has this ability.
Some ecu's automatically advance the ignition until the engine just starts to pink ( thats what the knock sensors are for) and then the ignition is retarded ever so slightly. In this case the engine would retune itself to run a higher octane fuel.
Cheers,
Tony
I dont know if the Jag ECU has this ability.
Some ecu's automatically advance the ignition until the engine just starts to pink ( thats what the knock sensors are for) and then the ignition is retarded ever so slightly. In this case the engine would retune itself to run a higher octane fuel.
Cheers,
Tony
FWIW I reckon Optimax works pretty well 
My blow-by test when I bought the car nearly two years ago was 15..
...but at the last service it was down to 10 and I have fed it Optimax all the time, so I think it not just about the extra 'oomph' but the fact that it burns cleaner as well and seems to suit the XK.
My blow-by test when I bought the car nearly two years ago was 15..
...but at the last service it was down to 10 and I have fed it Optimax all the time, so I think it not just about the extra 'oomph' but the fact that it burns cleaner as well and seems to suit the XK.
I used Optimax since I bought my car in the belief that it was a worthwhile investment to help protect the engine.
Since the engine went bang, I've mostly used '97 in the new engine and it feels no different. I just put the occasional tank of Optimax in for the cleaning qualities.
PS: By far your biggest monetry concern should be getting those tensioners changed!
Since the engine went bang, I've mostly used '97 in the new engine and it feels no different. I just put the occasional tank of Optimax in for the cleaning qualities.
PS: By far your biggest monetry concern should be getting those tensioners changed!
dunno about a new jag like yours Pwig, but have found that my old V12 loves the stuff ....
I see a better gas milage rate over a long term test, but most importantly if i put inferior stuff in it realy makes a difference. ...
Had teh misfortune of having to fill up in the midlands one time, very low and all teh petrol stations i went to only had cr@p 95ron.
After half a tank the engine started sounding like a ropey old V8 ... then when stuck in Birmingham in a traffic jam the misfires got so bad that it was almost stalling teh car ....
Refuled at teh end of the day with Optomax and hooned back to London, and all was better ...
It does take 2 or 3 tanks worth to flush the system and actually get the detergants coating all the components properly.
Should add for disclosure that I work freelance for Shell, but that i have been using Optomax long before i started at Shell, and even when working for other oil companies i used Optomax.
I see a better gas milage rate over a long term test, but most importantly if i put inferior stuff in it realy makes a difference. ...
Had teh misfortune of having to fill up in the midlands one time, very low and all teh petrol stations i went to only had cr@p 95ron.
After half a tank the engine started sounding like a ropey old V8 ... then when stuck in Birmingham in a traffic jam the misfires got so bad that it was almost stalling teh car ....
Refuled at teh end of the day with Optomax and hooned back to London, and all was better ...
It does take 2 or 3 tanks worth to flush the system and actually get the detergants coating all the components properly.
Should add for disclosure that I work freelance for Shell, but that i have been using Optomax long before i started at Shell, and even when working for other oil companies i used Optomax.
groomi said:
I used Optimax since I bought my car in the belief that it was a worthwhile investment to help protect the engine.
Since the engine went bang, I've mostly used '97 in the new engine and it feels no different. I just put the occasional tank of Optimax in for the cleaning qualities.
PS: By far your biggest monetry concern should be getting those tensioners changed!
Speaking of tensioners, how much are we looking to change them? Most places seem to be charging about £1200?
pwig said:
Speaking of tensioners, how much are we looking to change them? Most places seem to be charging about £1200?
Pwig, at the risk of going a little off topic
... That seems to be the going rate for a full change (primary and scondary, plus chains) from an independent. (I think a member of www.xkec.co.uk got near that price from a main dealer too!
) You can get it cheaper if you just want secondary's changed - I think David Marks Gargages do it for about £400, Elite will probably do it for similar money.
Rgds
banny said:
Yes the Jasg does auto adjust by means of the knock sensor.
You are not wasting your money but the gains will be difficult to notice.
Must admit to only using optimax.
Bollox!
Pwig, ask the person who knows, your engine is the supercharged AJ26 which means it runs 16 bit Nippon denso engine management.
It DOES have knock sensing, but it wasn't calibrated to run INTO and out of knock actively as a strategy. It was calibrated to run on 95 octane and will provide very little benefit if you run 98.
My Mercedes (1990 190E 2.5 "cossie"
has an adjustment switch under the bonnet for the octane of fuel you are using. It has 7 settings including 'N' (normal octane) and 'S' (super unleaded). It goes right down to '1' for, presumably, stagnant crude oil 
.
Never seen this switch on any other cars but, now you know it's a possibility.
All it does is adjust the timing, which is easily done. So if you want to run optimax and aren't sure if the engine can automatically adjust to it, get the engine timing adjusted to run high octane. Then you'll know its definitely taking advantage of the extra power available.
>> Edited by pentoman on Monday 13th March 10:47
has an adjustment switch under the bonnet for the octane of fuel you are using. It has 7 settings including 'N' (normal octane) and 'S' (super unleaded). It goes right down to '1' for, presumably, stagnant crude oil . Never seen this switch on any other cars but, now you know it's a possibility.
All it does is adjust the timing, which is easily done. So if you want to run optimax and aren't sure if the engine can automatically adjust to it, get the engine timing adjusted to run high octane. Then you'll know its definitely taking advantage of the extra power available.
>> Edited by pentoman on Monday 13th March 10:47
pentoman said:
My Mercedes (1990 190E 2.5 "cossie"
Never seen this switch on any other cars but, now you know it's a possibility.
All it does is adjust the timing, which is easily done. So if you want to run optimax and aren't sure if the engine can automatically adjust to it, get the engine timing adjusted to run high octane. Then you'll know its definitely taking advantage of the extra power available.
>> Edited by pentoman on Monday 13th March 10:47
Agreed, if you can adjust the ignition to run on it.
Is your Merc K Jetronic? I think it also has an ignition module, EZK or LZK or something.
Unfortunately the Jag can't be adjusted in this manner. The Jag ECU has been deliberately sealed to stop this kind of thing, even at Jag Whitley the person capable of reflashing production ECUs kept the procedure closely guarded.
pentoman said:
My Mercedes (1990 190E 2.5 "cossie"
Never seen this switch on any other cars but, now you know it's a possibility.
All it does is adjust the timing, which is easily done. So if you want to run optimax and aren't sure if the engine can automatically adjust to it, get the engine timing adjusted to run high octane. Then you'll know its definitely taking advantage of the extra power available.
>> Edited by pentoman on Monday 13th March 10:47
My old Vauxhall Caviler(sp) had a simpler version of this. Can't remember the year, it was an F Reg. Anyway there was a jumper for either 95 or 98 octane. This made a huge difference to both the economy and the power output. On "normal" 95 octane it used to do 350 miles on a tank if you were lucky, on 98 octane it always bettered 500miles. The performance difference was similar, in a later one I could keep up with the bosses 16V Calibre which was supposed to have a 30BHP advantage in bascally the same car.
Another guy in the office was unlucky though, his one had a jumper for either 92 or 95
Marquis_Rex said:
My Mercedes (1990 190E 2.5 "cossie"
Never seen this switch on any other cars but, now you know it's a possibility.
All it does is adjust the timing, which is easily done. So if you want to run optimax and aren't sure if the engine can automatically adjust to it, get the engine timing adjusted to run high octane. Then you'll know its definitely taking advantage of the extra power available.
>> Edited by pentoman on Monday 13th March 10:47
Agreed, if you can adjust the ignition to run on it.
Is your Merc K Jetronic? I think it also has an ignition module, EZK or LZK or something.
Unfortunately the Jag can't be adjusted in this manner. The Jag ECU has been deliberately sealed to stop this kind of thing, even at Jag Whitley the person capable of reflashing production ECUs kept the procedure closely guarded.
That sucks.
My 2.0 is K-Jetronic, the 2.5 is KE. The ignition system is EZL. Sorry that this is so boring for anyone other than me and rex!
pentoman said:
.. Sorry that this is so boring for anyone other than me and rex!
Not at all pentoman,
Can someone tell me then... is my 97MY XK8 adjusting for the fuel or not
If not, does that mean it is running a bit rich or what? It certainly goes better on the stuff and my blow-by test has dropped.
Cheers all
robocop said:
.. Sorry that this is so boring for anyone other than me and rex!
Not at all pentoman,
Can someone tell me then... is my 97MY XK8 adjusting for the fuel or not
If not, does that mean it is running a bit rich or what? It certainly goes better on the stuff and my blow-by test has dropped.
Cheers all
I can't explain your experiences but your engine is also an Aj26 with 16 bit and shouldn't actively go into knock if you run 98 octane. Also because it's naturally aspirated, its likely to show even less benefit if it did actively go into knock.
Marquis_Rex said:
.. Sorry that this is so boring for anyone other than me and rex!
Not at all pentoman,
Can someone tell me then... is my 97MY XK8 adjusting for the fuel or not
If not, does that mean it is running a bit rich or what? It certainly goes better on the stuff and my blow-by test has dropped.
Cheers all
I can't explain your experiences but your engine is also an Aj26 with 16 bit and shouldn't actively go into knock if you run 98 octane. Also because it's naturally aspirated, its likely to show even less benefit if it did actively go into knock.
Rex - I sent you an email.
You don't have to adjust your engine for higher quality fuel - you just won't get the best out of it.
Basically (I might get some of this the wrong way round), you want the engine to spark as late as possible for best combustion and most power. However, leave it too late, and the petrol will ignite on its own (like diesel does, which makes the 'knock' sound which sounds like a diesel car). This self-ignition is uncontrolled and can cause engine damage, so you try to avoid it. However you try to get as close as possible to it so you get max power.
So you (or your engine's computer) adjust the ignition so it sparks as late as is safe. Higher octane fuels can be left later because they are more refined and less prone to self ignition, so generate more power.
So my point is, if your car does not adjust for the fuel type and you run on 95 octane, it is not a problem, so long as it is not thinking that you are running on 97/98 octane!
Russell
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