MONDEO TDCI Mk 4 DIESEL - Erratic Temperature Gauge

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Fri 1 Jan 2016 22:04
MONDEO TDCI Mk 4 DIESEL - Erratic Temperature Gauge - mr jinks

Hi

My 09 tdci Mondeo MK4 has a strange temperature gauge issue.

Sometimes it will appear ok (it never goes past halfway) but most other times not really.

Usually it will warm up fairly slowly and only get up to halfway when at speed (60+), slowly dropping down to 1/4 or just below when encountering towns/traffic and driving at a lower speed, but occasionally it does spend most of the journey at halfway, but will never stay there.

The car drives without fault apart from this minor issue and both heater and aircon work fine - there seems to be no noticeable effect if I have heat/aircon on or not. It has relatively newish coolant (usually at the right level or thereabouts).

Any thoughts? I've had a quick look online and it seems it could be a trial and error job - possibly a faulty sensor/connection, thermostat (less likely) or the instrumnet panel itself.

Thanks, semi-baffled.

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Fri 1 Jan 2016 22:56
MONDEO TDCI Mk 4 DIESEL - Erratic Temperature Gauge - elekie&a/c doctor
I would consider the thermostat as the first check.perhaps get some diagnostic /scan tool plugged in to check real time actual value of coolant temp.
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Sat 2 Jan 2016 09:33
MONDEO TDCI Mk 4 DIESEL - Erratic Temperature Gauge - Fernando P

Also check for airlocks in the cooling system.

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Sat 2 Jan 2016 10:07
MONDEO TDCI Mk 4 DIESEL - Erratic Temperature Gauge - hardway

You say "thermostat less likely",

Odd as I would condifer this as classic symptoms of a partially stuck open 'stat!

Working 'stat only circulates engine coolant until aprox 90 degrees,

So gauge ought to rise relatively quickly to normal operating temp then drop as the 'stat opens to the Radiator,

then rise again to normal operating temp,

which is where it stays unless it's a hot day,

your stuck in trafic,

or high engine revs,

when the rad fan should kick in to drop the temp to normal operating temp.

If the 'stat is stuck open the rad system is included in the coolant circuit so the entire coolant cuircuit NEVER reaches operating temp unless you hammer it until the engine temperature does actually rise to where it ought to be.

I run a rough coolant test by starting the car,

leaving it at idle while monitoring to temp,

which should rise and fall/rise again as stated,

then the rad fan should kick in then switch off when cooled some.

But as this is winter it might need a 5/10 min' high idle to get the gauge up.

I'm betting yours never gets hot enough to kick the rad fans in.

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