So, wanting to look at battery voltage, I installed one of those ODB gauge apps on my iPad, hooked up my Kiwi bluetooth module and went out for a 10 mile drive.

Battery voltage is lovely. No problems there. But then I noticed that the coolant temperature was running between around 83 and 87 centigrade, settling at around 85 driving steadily at 40 mph . This is too low, yes?

I didn't do any spirited driving (iPad on my lap!) so maybe the car wasn't really warmed up. But I read that the 5.0 has a fast warm-up time and I imagined I'd be seeing something over 90. When I got back and parked up, the temperature did eventually rise to 90 centigrade idling on the driveway, but still...

 

Other may vary in their opinion but I am only ever bothered about engine temperatures which are too high. 40mph will definitely not be taxing the cooling system. If the air blowing out of the heater vents starts getting warm after a minute or so in cold weather, then it means that you do have a thermostat fitted and that it is opening and closing properly. Of course, it all depends upon the ambient temperature as well.

Richard

 

@RichardS thanks very much for your response, which is reassuring. My suspicion is that the thermostat may be "on the way out" e.g. not fully closing, and that sooner or later I'll have to replace it. As you say, running somewhat cool isn't a big deal (compared to running too hot at least) but it will be affecting efficiency, especially on short low-speed runs to the shops etc.

The heater does blow hot soon after starting, and engine management has displayed no signs of disquiet. I'm going on a longer trip today (which happens to be a cold day; 6 degrees C in the garden right now) and I'll be driving for a time at speed, so I'll check the temps when I get back.

 

Why not take the iPad along? You don’t have to watch it constantly.

 

So, after a burn up coming back from Leatherhead, temp reading is 92. Still lower than I might have imagined, but all seems well. I'm going to keep an eye on it though; I still suspect there's a thermostat change in my future sometime.

 

Justin:
Here's a screen shot or my 2008 4.2 XKR showing voltage and temp.

Default gauges on my OBDLinkMX+, Coolant temp is great to see!
XKRICK

 

You're seeing 94C on your car - which is great.

The service manual (for the 5.0) says the thermostat starts to open at 88 - 90C and is fully open at 102C. I infer from this that Jaguar intends the running temperature to be regulated somewhere north of 90C. If while I'm burbling around town doing my errands I'm seeing 85C then the thermostat hasn't even started to open - unless my thermostat doesn't close completely. Either way, the engine is running cold.

I'm probably fretting about nothing. As I said above, I'm going to keep an eye on it. I might set up the app to log temperature and speed and then go for a run, to see how quickly the engine warms up.

 

For what it's worth; my 2013 XKR runs between 190f and 210f depending upon speed, traffic and ambient temperature in So Cal.

 

Not awfully familiar with the cooling circuit of the X150 5.0 litre cars, but on the Rover with the same engine, there's 2 sensors, one for the heater manifold and one for the electronic thermostat. I find the thermostat temp typically remains quite cold compared to the manifold temp and only increases whilst idling stationary for prolonged periods.