So I guess it's time to admit that my S3 is guzzling far more fuel than it should! (I think).

I've only owned the car for two months so far and from working things out I believe I am getting between 25-30L/100km / 8-9mpg. This is mainly city driving.

What can be done to improve this? I believe it could be running rich (how to check - spark plugs out?)

What has been done to the vehicle since I got it (that may affect consumption):

• Oil Change
• Spark Plugs (old ones were OK brown colour)
• Oil & Air Filter
• Coolant Flush

I've noticed that the engine does take quite a while (maybe 10km / 6mi city driving) to climb up to the 90 degree mark. Perhaps I have a thermostat stuck open? Would this affect consumption?


Thanks in advance guys.

 

Oliver,

The temp of the FI engine will have a marked affect on fuel usage. The S3 likes to run in that 90c range, and an 88c stat is what is called for.

I have just had that with a S3 XJ6, using excessive fuel, and the gauge was below that "green range" by about 2 needle widths. Fitted an 88c stat, NOTHING else done, and now he reports a significant decrease in consumption.

Others I have owned, carby and EFI, have had a slight increase in economy by using a 15W/40 oil, in lieu of the 20W/50.

The obvious other points are:

Tyre pressures.
Ignition timing, maybe its retarded a tad, that will do it also.


On a larger scale, the camshaft timing may be wrongly set. This I have seen many times. The "dialing in" of the 2 sprockets is a little time consuming, but well worth getting spot on.

 

Thanks Grant. The engine does however get up to 90c (middle) when sitting in traffic, etc but when moving at any speed it will drop below that again. (70km/h +).

Do you reckon I have a lower setting thermostat or that perhaps its stuck open? How easy are these thermostats to replace on an XJ6?

 

If its moving around like that it is palin worn out.

They are not that hard to replace, just fiddly and time consuming, and then the rusted bolt/s, usually the bottom one, and the one nearest the head, and if they break off, there goes another day to get them out.

Check that fan clutch also, as it may be getting tired, and they can either seize or just go really free and spin uselessly.

 

Thanks Grant. I guess that's as good a place to start as any.

 

Make sure to drain the coolant below the level of the thermostat, (sorry I'm sure you already know to do this,) if you don't it'll leak all over the distributor and that's not something you want corroded and gunky. Also you'll want to get two gaskets, one for either side of the thermostat housing, the whole thing comes out when you remove the two bolts. I just stenciled out the gasket from each side of the housing and cut it with an exacto knife from gasket material, only cost 99 cents and was easy and I didn't have to order a specific gasket(s). Also, check the two heater hoses that connect to the housing, they might need to be changed while you have them out, good preventative maintenance, and killing two birds with one stone is always good =)

 

Thanks for the advice guys. I will try to get this done this weekend. Is it a specific thermostat or can I pick up a generic from Autozone? The temp definitely drops quite a bit when the car is at speed.

 

It is not that specific in the parts world.

I use the Dayco DT18A, which is a 82c stat.

Another is Tridon brand TT228-180, is also what I have used on the V12's, same stat, just 2 of them.

I would also consider the DT18G, which is a 89c stat, of the same family. The S3 will drink fuel if running tooooo cold, as you already know.

When you go to source the stat, forget Jaguar, they will say, "no way man", so just give them the part number from above and let them convert that number to whatever brand they stock. It really is not that hard for them.

 

good advice grant, I hate the preconceptions some people have towards jaguars, and the affect it can have on price, parts or labor, that's why I do it all myself, its a car not an ancient alien artifact for goodness sake!

 

YEP, You forgot the most important thing.

Jaguars are ALL female, think about it.

Time for work, see ya.