8 replies to this topic

[graphitemondeo15]

My mondeo tdci auto has had an mpg of around 35 mpg since i bought it, recently it has dropped to 25 and only rises to around 35 mpg when i'm on the motorway, it has a known thermostat problem which i am planning to sort asap but i have never known a thermostat to cause such an issue, the car is serviced regulary, is 100% stock, i've cleaned the EGR and intake manifold to no avail, does anyone have any ideas as i could afford the car but now i cannot justify the running costs and may have to sell it.

[PURPLE_2L_LX]

Short journey's? Kills the MPG. Winter fuel seems worse than normal also.

Do you have the fuel comp or working it out yourself?

Mine was down to 26 - 28mpg last winter. How long do you leave it ticking over to warm up and doing zero mpg?

I lost 2mpg waiting for the front heated screen to clear.

[Gary Price]

Definitely sounds like you have a problem.

My thermostat is not as good as it should be, takes a long time to get up to temp and drops when going slow.
Even so I am still getting 55 mpg average. I only got a few mpg more in the summer.
It does depend how fast you drive but I seem to get about 60mpg at 60mph or 50mpg at 80mph.

It might be worth changing the thermostats but they are expensive. There are 2 and its recommended that genuine Ford ones are used expect about £50 for the 2.

If you had a serious engine/fuel problem the engine management light (EML) would be on.

Its possible your brakes are binding.
Jack up the wheels one at a time while cold to see if they turn freely,
Then repeat after driving a few miles. The rear ones seem to be the most common culprits.
Hand brake cables can jam and pistons can seize in the callipers.

Split turbo hoses are also worth checking for, I've not had this problem myself but usually there is a noticeable whoosing noise, loss of power but the EML light does not come on.

Good luck

Gary

[graphitemondeo15]

I do relativly short journeys (10 miles) commuting, but checked (calculated myself) mpg over a long run up to scotland and not any improvement. The car is parked in a garage so there is little to zero warm up time before it has an mpg above zero, checked all intercooler pipes as i had to replace the egr/intercooler pipe recently, also noticed when i took the car out last there is what sounds to me like a loud diesel knock when i accelerate for the first mile or so. Would this be a warning sign of anything? will check the brakes in the morning and any other ideas would be useful

[Dices]

Do change the thermostat first because a cold engine pulls down MPG dramaticly and driving an engine constantly or longer than necessary below normal temp creates lots more engine wear. After you know your therm. is ok you can search further.

[mr_dilz]

My thermostat is also suffering from yoyo like symptoms especially when going slow or coasting downhill and the engine is not in use. Also i have noticed that my temp guage never seems to go below -2c. I know for a fact it has been colder than that when I have been driving.

[Dices]

Your outside temp and thermostat are 2 different things, Outside temp is a sensor usually somewhere behind the front bumper. The thermostat is a kind of valve in the coolant of the engine. That shows 60°C and up to ( I think) 120°C on the dash. If that doesn't work properly it stays open and your coolant temp doesn't reach operational temp. especially with weather like this.

[Mondy55]

 mr_dilz, on 08 February 2012 - 04:36 PM, said:

My thermostat is also suffering from yoyo like symptoms especially when going slow or coasting downhill and the engine is not in use.

To me that sounds more like the temp gauge sender rather than the thermostat itself.

[mr_dilz]

I think I have two issues - temp guage giving not accurate temperatures - i.e. not going below -2c. I have never seen it go below -2c.

I think I also have issue with thermostat is it does reach 90c when car is warmed up, but if i drive slow or coast or go round a bend even and lift off power, then the needle does drop. I am sure this did not happen before.