[Engine] Coolant Temp Gauge Maybe Not Working or a Stuck Open Thermostat

[IHateMyDadsM59Berlingo]

The Mighty DV6B has suffered with this issue according to my dad for years ever since it ran out of coolant due to a leak in the corrugated coolant manifold down the back of the engine, It didn't overheat at least as he's aware which is the problem. Now The van has ran about the town for most of its life until my dad retired. Now he's allowed me to drive it since him and the vans retirement I'm struggling to figure out if it could be the temp sensor or the Thermostat being stuck open after a good run up the motor way at 65 ad 70 MPH which its running between 2500 and 2850 RPM . The fact hot air does eventually after a 20 or 30 min drive hot air does start to come through suggest to me its stuck open but if after a good drive leaving it to idle for 20 mins brings the temp gauge up to about 70 degrees and I'm sure if I could be bothered to sit there for half an hour or more at idle it would reach 90 degrees which it should as I'm aware from pervious experience from PSA cars, but the second you move off it crashes down to the cold or just above. I have never heard the coolant fan run in almost 10 years and there is no code for the coolant fan resistor failing. Is it a fact its so under powered and under strained it just doesn't get hot for a long time or are one of my suspicions correct?.

[jj9]

From your description it does sound like the thermostat is letting by.

Feel the top hose and if it gets warm before the thermostat would normally open (around 80 -90°C) then the thermostat is letting by.... this is difficult to judge accurately by hand as the heat from you hand gives you the impression that it is heating up !

Place a piece of cardboard over the front of the radiator when driving from cold this will block any air to the rad and you should see the temp rise quicker than normal.


Cheers.

.

[smutts]

Just for the record, the 1.6hdi's normal coolant temp is 82 degrees......ish.
Part number is "1336AF" for the thermostat, at least for mine (DV6TED4 crossed with a Volvo variant; ....don't ask!)
It's a stupidly overcomplicated (therefore expensive) mass of welded plastic hiding a bog standard £5 thermostat.
some Ford, Fiat, Volvo, Suzuki, Mazda, Mini, used the same 1.6 diesel engine, so Ebaying might find the same part cheaper.
Good luck.