Yet another 2.4JTD thermostat question
Have not had this car long (2.4 175 MJet) and trying to explain the ****ty mpg. Am planning to change the thermostat as a starter, but want to be a bit sure before I start flinging large lumps of cash around (bankrupted myself doing that on a Volvo T5 years ago, so many sensors, MAFs and ECUs...and multiples of £150)
Thought I'd do a test this morning to see how quickly the guage rose, and establish when the thermo opened. Ambient temperature was 12 degrees according to my thermometers, one in the cabin and one taped to the top pipe.
Sat on the drive , let it idle for 8 mins, then a fast rev for 3 mins, another 3 min idle, 3 min fast rev etc. It took 23 minutes for the needle on the guage to even move (just touched "50", I know the calibration is only average), and the top pipe was stone cold. By this time I had to get to work, so drove a ile up the road, noticed the guage had moved to the next increment (70?), stopped and the thermo had just opened, top pipe warmish. All the way to work it never touched 80.
Now my idea of a stuck open thermostat is that heat starts coming through more or less straight away, and that temeratures rise dramatically in traffic. Even in standing traffic this car never gets hot, the engine just does not seem to produce heat. The cabin heater worked to a toasty level after about 10 mins, but then according to the manual it has a secondary heater somewhere, something to do with the two 30A fuses on the bulkhead.
I usually change thermostats on all secondhand cars I buy, usually as it costs about a tenner and never otherwise gets looked at. Having said I only ever really noticed a difference when swapping from an 88 deg to a 92 deg winter thermo on my Volvo, but it was a cheap peace of mind. There now seems to be an alarming trend to make them part of a much larger casting or ever more complicated component which really makes you think twice.
I have searched all the old threads about this but have seen enough "I swapped it and nothing changed" replies to cast doubts. There are no clouds of smoke, just the odd puff you would expect from a large capacity diesel, so I was discounting the MAF