Chrysler 300C & SRT8 Forums banner

1 - 10 of 10 Posts

·
Registered
Joined
·
34 Posts
Discussion Starter #1
Had my beasty for 2 years, done 45k miles and been averaging all that time approx 32mpg (never reset the mpg on the computer all that time). Last two weeks I noticed it dropping to below 30mpg. Reset the MPG and I am struggling to get it above 28mpg combined. Just had a service and they found no issues so need some ideas form the "brain trust" please as to what to look for.

Something must of happened as its a sudden decrease not a gradual.

Cheers
Steven
 

·
Registered
Joined
·
3,666 Posts
I wouldn't call that "dropped off a cliff". You're comparing a long-term average with a short-term average and there's no guarantee that they will be close. A short-term value will be influenced by driving style, traffic conditions, length of journey and at this time of year, weather. Over the past couple of weeks my mpg has dropped by a similar amount, which I have attributed to colder weather, longer nights and shorter trips. The 1kW electric cabin heater and rear screen heater will provide a heavy load on your alternator, not to mention any use of the seat heating. Have you checked your tyre pressures and not just by the EVIC, but with a manual gauge? Pressures will be reduced in cold weather and this can have a negative effect on mpg. I don't think you should be too concerned about a variation of 32-28 over a short term.
 

·
Registered
2014 CRD
Joined
·
1,476 Posts
Mine drops one or two mpg when it's really cold too. Also have you checked tyre pressures?
 

·
Registered
Joined
·
34 Posts
Discussion Starter #4
I wouldn't call that "dropped off a cliff". You're comparing a long-term average with a short-term average and there's no guarantee that they will be close. A short-term value will be influenced by driving style, traffic conditions, length of journey and at this time of year, weather. Over the past couple of weeks my mpg has dropped by a similar amount, which I have attributed to colder weather, longer nights and shorter trips. The 1kW electric cabin heater and rear screen heater will provide a heavy load on your alternator, not to mention any use of the seat heating. Have you checked your tyre pressures and not just by the EVIC, but with a manual gauge? Pressures will be reduced in cold weather and this can have a negative effect on mpg. I don't think you should be too concerned about a variation of 32-28 over a short term.
Bit dramatic I agree. for the first 45000 miles it was averaging 32-34 on the computer, then in the space of 1 tankful that 45000 mile average dropped below 30mpg, that tankful was driving to Paris so mostly constant 85mph cruising. I will leave the computer running now its been serviced to see if it creeps up, just seemed to me that it feels like something changed or happened to create the decrease as so out of character to the previous 2 years.
 

·
Registered
Joined
·
773 Posts
Bit dramatic I agree. for the first 45000 miles it was averaging 32-34 on the computer, then in the space of 1 tankful that 45000 mile average dropped below 30mpg, that tankful was driving to Paris so mostly constant 85mph cruising.
There's your answer. I suspect you normally cruise here at a slightly lower speed?
 

·
Registered
Joined
·
34 Posts
Discussion Starter #7
ahhh no, normally a tad higher over here if not the same :p
Right so I am still struggling to get above 28.8mpg on a tank of combined driving. Something is definitely different than before.

Last night I undertook a test, cruised at 80mph for 3 miles on cruise control and averaged 30.4mpg. That is not right, over the 450000 miles previously, 70% was motorway and most of that was 80-90mph driving. I should be able to get over 30.4mpg at 80mph.

Tyre pressures are min 2.4
Brakes not binding as had them checked
Serviced 500miles ago

so my thoughts are;
1 Fuel Leak
2 Running rich (if it can with a diesel)
3 Whatever it does when the engine is cold is not shutting down when the engine is warm
4 ECU is on its way out
5 Startech Sd6 box is on its way out

Thoughts?
Steven
 
1 - 10 of 10 Posts
Top