The mpg quest

[Jeffyjazz]

I'm still hunting for my missing 20mpg that I seem to have lost.  I used to get about 60 and recently only been getting 40 same 35mile journey  each way all motor way except for the first 1/4mile

My next task is to put a new radiator in as I noticed that mine has no fins left, I'm guessing this would make the engine run hotter but would hotter reduce mph??  I've noticed that the centre console but  in front of the gearstick with the two cup holders gets really hit by the time I get to work. Hot enough that my trouser leg is warm and I can feel the heat radiating off it on to my leg.  Could this be a sign of the engine running hot

Also since the cold weather is coming in the mpg has gone up to around 46 so it's kindling if pointing to a heat issue, normally cold weather uses more fuel??

Any thoughts?? I have the new radiator just got to fit it

[culzean]

Colder weather reduces MPG,  hotter engine may make MPG higher.  If the engine radiator fan has not been cutting in (you will hear it  if in doubt turn aircon off because aircon will make both the engine fan and aircon fan come on) then assume engine is not running too hot (don't know what Honda were thinking not fitting a proper temperature gauge to Jazz,  a temperature light that is either on or off falls straight into the 'chocolate teapot' category),  the ambient temperature in UK is such that you may not need the whole radiator to have fins anyway (I can remember when it was common to block off the radiator in winter,  special 'radiator blinds' were sold, which could be raised or lowered from inside the car,   but most people used cardboard, aluminium foil or whatever else was at hand).

I know I am beginning to sound like a broken record on this,  but try Redex system and injector cleaner,  it is fairly cheap and if it doesn't show improvement within a week you haven't really lost a lot.

[guest1372]

I have the early side by side radiator & a/c matrix and am missing a fair amount of the driver's side a/c matrix fins, but the passenger side radiator is OK.  I thought the fan switch had failed (on the side of the block below the throttle) but specs show it does not kick in until 95° and the car just doesn't seem to get that hot, usually 87° or 88°.

The OBDII code reader provides live engine temperature and near-instant mpg readings so might help with trouble shooting if you have a smartphone showing the data while driving.

The cup holder area has the cabin heater ducts just above it maybe one of the heat selector cables is detached; 2nd nearest thing to the cup holders is the catalytic converter, it's fairly close to the bulkhead.  If the pre & post cat sensors are out of bounds the code reader should note this, but there is no live data for them.  It could be having to work harder to remove excess HC/NOx produced by an inefficient fuel burn. 

Still grasping at straws but I could lend you a spare EGR valve if that's something you suspect.
--
TG

[CRC]

Generally, there are two scenarios that would result in fuel economy.

1. The engine is running fine, but it's having to work harder to get from point A to point B.
2. The engine is not running fine.

In the first instance, the engine may have to work harder due to some other factor, for example a sticking brake caliper that is generating heat, very underinflated tyres, much higher speeds causing extra wind resistance etc.

Of these things, the sticking brake is the favourite, but is easy to detect when coasting / pushing the car and very easy to detect just by touching the wheels after a run. ( I once burnt my fingers touching the back wheel of an Integra with sticking brake pads.)

If the car seems to roll along fine, then logically the engine must be squirting more fuel in per revolution, and one of the favourite causes for this is that it's getting duff information from the engine temperature sensor, which is telling the ECU that the engine is cold and that it needs a rich mixture to keep it running.

However, the car would normally run really rough when ticking over ( like pulling out the choke on an old car), and would be very noticable.

Apart from the mpg figure (assume that is the onscreen display), are there any other symptoms and does the onscreen display match up with a "brim to brim" mpg assessment as done in the old days?

[Jeffyjazz]

Engine runs fine and sounds fine certainly no sticky mechanical bits. I've tried tires from 30psi up to 36 and it didn't really make much difference so I have put them back to about 32 

It might just be as the engine is older now it's just hit 123k most of it motorway miles

The spark plugs are pure white which is odd they just look brand new,  they used to be a browny/tan color. I have got a non genuine cat on it but can't remember if that coincided with the mpg drop but that's the only thing I can think of now

[jasonevans]

I'm getting between 43-48mpg in mixed town driving but have never got over 53mpg for a sustained period of time, not even on the motorway. 

[Jeffyjazz]

Hmmmmm this is getting weirder
Put a new back box on yesterday as mine snapped
And look what happened 65.1mpg!!!!!

[attachment deleted by admin]

[Jeffyjazz]

I replaced a bosal one with a cheap as chips bean can one. £27
Will probably only last a year but should be alright.   It's interesting that it has a strengthening gusset weld on but the the bosal one didn't.   Dodgy looking pigeon poo welding though lol

[attachment deleted by admin]

[guest1372]

The extra bracket looks like sense as they all seem to snap at the box/pipe joint then drag on the ground.  Maybe the old one had somehow got blocked up with rust?  Anyway good news if that's fixed

Make sure your spring joint still flexes a bit and is not done up too tight.
--
TG

[culzean]

The extra bracket looks like sense as they all seem to snap at the box/pipe joint then drag on the ground.  Maybe the old one had somehow got blocked up with rust?  Anyway good news if that's fixed

Make sure your spring joint still flexes a bit and is not done up too tight.
--
TG

Could be the extra bracket is required with much thinner steel tube.  I know the OEM Honda exhaust has a spring loaded ball joint at the front which lets the exhaust flex and 'self-align' , aftermarket ones don't have the round bit on the end and don't move as well,  I have even seen exhaust fitters put something like fireclay sealant into the joint to stop it leaking,  which effectively takes all the movement out of it 

[Jeffyjazz]

Think I might loosen the flex joint tonight a bit as at about 3500 rpm it's makes s really deep resonating noise through the car.  It's not a touching banging noise just a resonance at about 3500rpm to 3600rpm then it's gone either side if that

It may just move rpms if I loosen it but will give it a go

Like a jazz tuning fork