Mondeo using more fuel

2003 Mondeo TDCi.

Over the last few days my car has started to use quite a bit more fuel, coincided with the start of the cold weather whether thats related or not. The trip computer usually says I'm getting on average 38mpg, this has dropped to 32-34mpg over the past four days. This is backed up by having to put more fuel in at fill up - about £2-£3 a night on 80 miles travelled (it's a taxi so brimmed at the end of every shift.). Turbo *seems* to be working, I can hear it spinning up as usual, and I can't notice any difference in performance. Theres no extra electrics being used or aircon, just the same as I always have. Other than the extra consumption I have'nt noticed anything wrong, no strange sounds, smells, warning lights, rattles or clunks. Oil and water levels correct. Spoken to other drivers with the same type of car and they're all running as normal. Any ideas?

Reply to
Kay
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The colder weather will make a difference to mpg, likewise will a lazy thermostat. What temperature is it running at?

Tim..

Reply to
Tim (remove obvious)

Quite possibly.

Would seem about right, especially if it's for short trips...

It would be unusual for a switch to winter diesel to make this much of a difference this late on...

Reply to
DervMan

The message from "Tim \(remove obvious\)" contains these words:

And diesels don't run rich while they're warming up like petrol engines do.

Reply to
Guy King

ISTR reading about getting more mpg in winter - IIRC "the calorific value of moist air was higher" or something along those lines

Reply to
Colin Wilson

Think that was a slight departure from the truth then but cold dense air will probably let the engine run more efficiently which will give you more mileage I suspect.

Reply to
Chris Street

Think I may have found the problem. Whilst checking the coolant level (engine had been running for a while) I noticed the water in the expansion tank was stone cold. After another 30 or so miles of round town driving I checked again and it was still cold.

Does this point to a faulty thermostat and, if so, would this cause the extra fuel consumption? Bearing in mind the sub-zero temps I've been driving around in does the thermostat still open to allow coolant circulation through the expansion tank, or does the ambient temperature mean it stays shut? Theres plenty of heat coming through the heater blower. The temperature gauge hardly moves above minimum, but then again it never has!

Reply to
Kay

up as well.Try this

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will sort it once and for all

Reply to
simondo

Probably, although I've known my Focus diesel to go twenty miles and still not got hot enough to open the stat and pass hot water to the radiator. However, see below.

Most Mondeo's seemed to come with a stat stuck open! My petrol one certainly did. I'd look first to getting the stat removed and swapped, or you can heat it in a pan of water on the stove to check it. It won't fully open until something like 103 degrees but at boiling point it should be mostly open.

IF the interior heater is hot and the gauge not moving then there could be a problem with the sender - it would be worth checking there isn't a bad contact or short. From memory the sender screws into the metal on the left end of the head - there is also a larger hex head which is the oil pressure switch. The CHT sender is the smaller of the two and more awkward to get at.

Reply to
Chris Street

On all modern Fords from about the mid 80's to now, the temp gauge is calibrated so it sits pretty much mid way when the engine is running at its designed optimum temperature.

The expansion tank should be the same temeprature as the engine pretty much- say at most 5deg lower, get a thermometer and stick it in to see exactly what temperature the engine is runnning at- immediately after a run of say

5-10 miles at atleast 30mph.

Should be 90deg+.

tim..

Reply to
Tim..

If you look at how the expansion tank is plumbed you'll see a small line coming from the block (probably top of thermostat housing ) into the top of the tank. Whilst the engine is running this line will be pumping coolant into the tank. Its purpose is to remove air from the system. Therefore this will be at the temp the enigne is at.

Tim..

Reply to
Tim..

My data book says thermostat starts to open at 88 and fully open at 103, so a expansion bottle of 90 sounds about spot on.

Reply to
Chris Street

I thought its purpose was to allow expansion of the coolant up the hose into the expansion tank hence the name.

Reply to
powerstation

And don't modern diesels also have a MAF, which would mean that colder, dense air will deliver a corresponding increase in fuelling?

Reply to
SteveH

YEs but on the Fords there are three pipes in, two are bleeds for air and the main fatter pipe is the main header feed.

The thermostat housing has a takeoff at the highest point to expel air and to ensure flow past the face of the thermostat - this dumps a steady trickle of coolant into the header tank due to waterpump pressure (tap is on the hot side of the loop)

Reply to
Chris Street

Which also means you get more power so actually need to use LESS throttle so you should BENEFIT from colder air with fuel economy.

Reply to
Conor

The message from "DervMan" contains these words:

Only when you're idling!

Reply to
Guy King

Hmm... so my new-to-me-this-summer Mondeo should be in the middle? it only gets just into the bottom end, but the heater is warm *enough*.

Not having had a Fraud since 1982 I wasn't sure where it would lie (I've had all sorts of cars with all sorts of 'standard' positions since then). How hard is it to get the stat out of a Mk1 2.0 Zetec?

Reply to
PC Paul

Yes as a rule.

Check its actual running temp immiediately after a run- should be around 90 deg.

3 bolts.

Tim..

Reply to
Tim (remove obvious)

'tis to Conor. 10% is,ooh, about 0.5mpg...

Reply to
PC Paul

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