Ford Mondeo 2.0 Tdci not warming up

Dilbert75

2013 Mondeo 2.0 Tdci (140)
280,000 kms
Timing belt and pump changed (Ford dealer) at 235,000 - Sept 18
Normal fuel consumption is around 5.8l/100km - first sign of increase was in Sept, started becoming more pronounced in November. Last tank was 6.35l/100km (10% higher). In the last 2 months I noticed that the engine temperature would drop as I was driving, recovering a few mins later. I thought the engine was slow to warm up - would be 10km in the morning before hitting temp.

Figured at the mileage that the thermostat might be getting lazy and sticking open or not closing fully. Ordered a replacement from MicksGarage - brand was Meat & Doria.

Brought it to a local garage last week to get it fitted. Fitting went fine and they did a test run afterwards - seemed fine. Apparently there's a bleed tube from the thermostat housing to the top of the radiator, to relieve any air locks and the need to bleed them. This was heating up when they tested it, implying that there was coolant flowing. That was on Saturday a week ago.

It seemed fine on Monday morning but on Monday evening I was coming home from work when, coming down a long hill, the temperature started dropping quickly - from full temp to below 60°C in about 2km (in gear but no throttle). Pulled over in case there was a leak and found the header tank was full and no apparent leak.

Drove to the garage and spoke to the mechanic. He couldn't understand it but verified that the heater was working - "if the heater is working, it's ok" was the mantra.

Worse Tuesday morning - slow to heat, temp dropping in transit, pretty much any time I backed off the accelerator. Was nearly in work (25km at 90/100km/h) before it hit full temp. Tuesday evening much worse - engine barely warmed up to full temp on the way home. Called and collected the old stat before it got thrown out. Temp way less stable since the new one went in so could have to change it back.

Found the diagnostics function in the MFD. On Wednesday morning I verified that the gauge sweep is going full scale on the temp gauge. Set it to engine temperature and watched the temp as I drove - the gauge pretty much mirrored the digital readout, so I believe it's reflecting what the ECU is seeing. (Also noticed the battery voltage was down to 12.1V, so ended up putting a new battery in too). Temp reading on the way home is generally much more consistently higher than on way in. This has continued since - temp gauge rarely reaching operating temp. Got the full 25km in this morning without it reaching temp. I know it was cold but it was never like this before. It loses temperature just sitting in traffic.

Mechanic was supposed to check with a Ford garage if they'd seen it before but hasn't come back to me. In my head it's one of three problems:
1) Not generating enough heat
2) Losing too much heat
3) Not correctly sensing heat

1) the fact that the cabin heater heats up within a couple of km would make this seem unlikely. The power seems normal enough too.
2) This could be possible. It wouldn't be the first time a new component was faulty. 3 litres of new coolant went in with the stat change but it wasn't that old anyway. It happens even if I drive with aircon off, so it's not that the heater is a major sink. Any other possible causes, other than the stat being dodgy?
3) Could it be that the coolant is the right temp but the car doesn't know it is? The thermostat came with a new sensor built-in. Could it be flaky? Could there be a bad connection somewhere? If it's under-reading temperature, is there a danger of it over-reading too?

The fuel consumption worries me. If the ECU thinks it's cold, will it over fuel and will that have other adverse effects (DPF blocking, for example)? I'm loathe to refit the old stat without good reason but is getting back to where it was the logical first step?

Thoughts? Experiences, especially with this engine in either Ford or Peugeot/Citroen?

Lewis_Benson

I have the same issue on my 2008 2.0 tdci mondeo.
Had the stat changed last year when the timing belt and water pump were being done.

That sorted it for about a week, and afterward it actually looked like it was running colder, my gauge sometimes doesnt get up past 1/4, and mostly sits close to almost looking like it's still cold.

I dont think its actually running cold though as if it was, i'd have mo heat in the car.

Dilbert75

Lewis_Benson wrote: »

I have the same issue on my 2008 2.0 tdci mondeo.
Had the stat changed last year when the timing belt and water pump were being done.

That sorted it for about a week, and afterward it actually looked like it was running colder, my gauge sometimes doesnt get up past 1/4, and mostly sits close to almost looking like it's still cold.

I dont think its actually running cold though as if it was, i'd have mo heat in the car.

Do you notice a difference in fuel economy? I'm trying not to correlate temperature and fuel use but there may be something.

Mine is frustratingly intermittent. 4°C going in this morning and it never went above indicated 75°C. 7.5°C on the way home and it was up to temp quite quickly (5km ish). Makes no sense to me.

Lewis_Benson

Dilbert75 wrote: »

Do you notice a difference in fuel economy? I'm trying not to correlate temperature and fuel use but there may be something.

Mine is frustratingly intermittent. 4°C going in this morning and it never went above indicated 75°C. 7.5°C on the way home and it was up to temp quite quickly (5km ish). Makes no sense to me.

Cant say I note any difference in fuel economy, because I dont believe the engine is actually running cold, i think the temp sensor is faulty.
Just havnt gotten around to doing anything with it.

junkyarddog

My 08 Mk4 2.0tdci does this too,
Although the temp gauge rises as normal to just under halfway,then drops back to just above the 1/4,then it fluctuates between the two.
It doesn't seem to have any effect on how it runs or on the fuel economy,
so I just treat it as one of those quirks that a car develops as it ages.