At the risk of beating a dead horse with this topic I'm wondering what other peope's fuel economy is with the car?

I recently did a 900km round trip mostly steep highway (1250m summit) driving and some city averaged 6.5km/L or 15.2mpg is this good for a car with 210000km on questionable injectors/fuel filters/regulators and oil leaks all around?

 

Hi Vancouver

On a run, I usually average 17.2 although around Town its much the same as you at about 15
and I'm also using Premium 99 Octane Gas.

So one of those 'slings and arrows' that you just have to learn how to live with or buy something else.



Its never a 'Cheap day out in an XJS'

 

I did 2000 miles in 2016 and averaged 7,3 km/l (20,6 UK MPG, 17,2 US MPG), everything included.
That is absolutely satifying for me. I did many cold starts and short drives, and on long drives cruising speed often is 80-85 MPH, so better numbers is possible. And no, we do not have a lot of police or cameras on the motorways...

 

Assuming we're talking about the V12s here.

17mpg city 26mpg highway here since eFan was installed. Was around 14.5 / 22 before that change. And it was as poor as 10.5 / 14 in the recent past.

Not a scientific study, many variables involved, and it's still not quite right.

 

My '85 with all the stuff done as far as catch up is concerned, returned:

Interstate runs 9kms/ltr, 25MPG Imperial.
Suburban running 7kms/ltr, 18MPG Imperial.
The BIG road trip, 25000kms, returned an average for the whole run of 10km/ltr, 29MPG Imperial.

When I first got the beast in 1994 the fuel gauge moved quicker than the tacho.

Efans, no emission stuff, 16CU computer, large throttle discs, cold air intakes, and so on.

 

Thanks, I've been gaining mpg since I first got the car it used to be as poor as 3 8km/L I could see hw efans improve things sadly the wait time is quite long for the quality dropin unit.

 

I assume you went over the Coquihalla? On the Vancouver-Calgary run I could get 22mpg ( imperial). If you're that low I would start by making sure your vacuum advance actually works. Both that it has vacuum ( the dump valve is a suspect) as well as the the advance mechanism works within the distributor. If we are talking strictly Hope-Kamloops, it will drop to about 17 mpg.

This assumed you have a Lucas distributor, as your car in an 89 you might have Marelli.

 

Marelli yes, hope to kelowna avg 6.5kmL there and 6.3 on the return trip. The car is in the shop for another task I might just have them go over your suggestions, I'm not as capable (yet) compared to their 40+ yrs exp.

I'm also running winter tires but in my experience anyone who claims tires make a huge difference is probably stretching the truth abit.

 

That's not a road that's good for fuel economy! How fast were you going? I find the fuel economy gets worse quite quickly over 110 Km/h.

Tires will make a bit of difference, but probably not more than 5%. Air filters and sparkplugs can make a difference too, I replaced plugs that had been in too long and I recorded about a 10% increase in fuel economy. I was surprised at how much difference it made.

 

Remember UK gallon is 4.5L and US gallon is 4.0L so mpg needs to specify which you are using L/100km or km/L is universal.

I average 12L/100km but thats mostly open road driving thats 8.3km/L or 24US mpg

 

My car has new plugs and new air filters and new rear tyres. On a 2,700 km road trip around Japan I averaged 15.2 mpg, though I don't know if that's US or UK mpg. That's including a lot of expressways, but also a fair bit of town and rural driving - normal rural roads in Japan are generally limited to 50 kph. For expressways only, I can average about 17 mpg. It will hit over 20 at times, but drop back down as soon as there's an uphill slope.
Makes me wonder if an electric fan would actually be a good idea....

 

This brochure has some mpg stats. They reckon 11.4 mpg around town, which is actually pretty much what I get (11.2 at the moment).
Jag-lovers brochures - a 1977 XJ-S Brochure Page
(That's for the pre-HE engine it seems. So I don't get good mileage at all....)

 

Other way around. UK gallon is 4.54 litres, US gallon is 3.78 litres. 160 vs 128 ounces, and the ounces are different too!

Agreed, metric is much easier.

 

I didn't know the ounces were different but that makes sense as the gallons are different.

We used UK here in Aus until the change to metric I remember as I was in year 6 at school.

 

My experience with 6.0 V12 (4 speed auto, torque convertor lock up clutch)

Was as follows:

urban stop / start up to 30mph typically returned 12mpg imperial)

cruise control at sixty mph (motorway) 25mpg
(boring, didn't happen often)

mix of urban and fast road / motorway about 18mpg.

Always surprised that 80mph gives better fuel economy than start stop urban.

Agree that with all vehicles above 70 to 80mph leads to large increase in fuel consumption due to wind resistance / drag.

Guess most of us didnt buy a V12 for fuel economy reasons.

I know given choice between saving fuel and 130mph plus on autobahns I'd opt for the latter anyday!

 

I have a '93 XJS 4.0 and I've probably been averaging 19-20mpg mixed driving.

 

I installed the trip computer in place of the clock panel a few years ago. 95 4.0 coupe commuting to work average 15.8 to 16.4 without my A/C on. It was lower than that but I now drive with the computer set to instantaneous to help me keep my foot out of it. I think it should be much better than that. Long trips it is about 20 with cruising between 75 - 80 using cruise control.

 

How easy is it to swap between the trip computer and the clock? I'd rather like to go the other way, I think.

 

Fuel economy?

 

If anyone else asks, I always say my fuel economy is "abysmal."

In honesty, though, I've been averaging about 15mpg, primarily due to a lot of stop and go traffic in my daily commute.