operating coolant temperature?

[Mark Dirac]

Does anyone know what should be the operating temperature of the engine (coolant) when the engine is "warmed up"?

My ODBII tells me that the thermostat is holding the temperature closely to 78 C / 79 C. Which sounds low to my mind.

So I am suspecting my thermostat, or perhaps the car's temperature sensor.

[Jocko]

With my Mk 1, I found it operated around 84-85°C but on shorter trips in the winter it was around 77°C. In queueing traffic, in the summer, it would get up to 90+°C. For the time of the year, yours sounds about right. I would need to do about 10 miles at this time of year to get to 84°C.

[pete-preston]

Hi Mark
How do you find the coolant temp gauge on the Honda Mk 4??  Have never see it on my wanderings thru the many
Screens/menus and have often missed the old temp gauge from previous cars

Thanks

[Kremmen]

As posted, it's from an ODB reader.

There is no temp gauge.

[Jocko]

I used to use my ScanGauge E which recorded the maximum temperature reached on a trip. It also displayed it in real-time, if selected. The ScanGauge also plugs into the OBD port.

[Zaier]

Hi Marc, the temperatures you're reading matches what I've read in my car, around 80° when engine is warm, with 82-85° peak while on motorway.
From what I've read, the thermostat fully opens at 78° so, it matches what we're observing.

[Mark Dirac]

Thanks for answering my question Zaier. And thanks to Kremmen for replying to pete-preston.

So, if my thermostat is opening at the same temperature as others, then I reckon there's a design flaw. Because...

My Jazz, just like many here, starts its engine just to provide cabin heat. So what? Well, my ODBII scanner reveals that this is happening even with the thermostat open. That's crazy. Instead of starting the engine to produce heat, it would be more sensible to close the thermostat.

I can drive 20 miles (country roads) with the coolant at operating temperature, at 78 degC, and yet the engine will still start when I start the climate control (AC off), and stop/EV mode when I turn the CC off. So the cabin heater is demanding that the engine starts up to generate heat even though the coolant is hot and indeed is being sent to the radiator to be cooled down.

It's as though the design is such that cabin heating demands and radiator cooling demands are not co-ordinated.

[Zaier]

It shouldn't behave like that, from what I've seen the demand of heat takes into account the external temperature and the temperature set on the climate control, so even in cold days close to 0° or a little below, the engine only warm up untill a certain temperature, and then shut down usually around 60°.
Which temperature did you set on the climate control?
I usually set it to 16° when I take the car in the morning (with recirculation on when possible), and then gradually increase to 18° and switching back to full auto cliamte as soon as the engine starts to shut down because it's warm enough.

[Mark Dirac]

It happens even at normal temperature settings such as 23C. Although it happens more if the dial is whacked up to "Hi".

If I'm descending a long hill, or crawling in EV mode in congestion, then it's fair enough for the engine to need to start up to generate some cabin heat, because the engine gradually cools down. But what I'm observing is that the engine sometimes starts up even though the engine is warm with the coolant temperature at 79C or close to it.

[Marco1979]

The engine will also fire up when battery level becomes too low. A higher ventilator speed can cause that to happen. So maybe coolant temperature is okay but the battery needs charging.

I use the heated seats for the first 2 minutes, then change to the ventilation system, trying to keep ventilation speed at 1 or 2 bars. Then I think the system operates just as intended. Haven’t measured coolant temp though…

[Mark Dirac]

The engine will also fire up when battery level becomes too low. A higher ventilator speed can cause that to happen. So maybe coolant temperature is okay but the battery needs charging.

I use the heated seats for the first 2 minutes, then change to the ventilation system, trying to keep ventilation speed at 1 or 2 bars. Then I think the system operates just as intended. Haven’t measured coolant temp though…

No, that's irrelevant to this puzzle. It's obvious that the engine will come on when the battery is low.

[Zaier]

It happens even at normal temperature settings such as 23C. Although it happens more if the dial is whacked up to "Hi".

If I'm descending a long hill, or crawling in EV mode in congestion, then it's fair enough for the engine to need to start up to generate some cabin heat, because the engine gradually cools down. But what I'm observing is that the engine sometimes starts up even though the engine is warm with the coolant temperature at 79C or close to it.

23° is a very high temperature if you're using the climate in "Auto" (as I do 90% of the time), I'll be sweating in my Jazz, I normally stay between 17° and 20° depending whether or not I'm wearing a jacket because it's a short trip.
HI kicks in the engine always especially in winter, it's an "extreme" setting meant to tell the car "heat me up as quick as possible".
Try lowering the temperature and leave the climate in "auto" to do his job, it should be better also for the engine kicking in.

Edit: at the same temperature setting on another car I'll feel cold, it's just the Jazz climate which looks to be more precise about the cabin temperature.

[Lord Voltermore]

I'd have thought Hondas primary concern is to ensure the ICE reaches  efficient, operating temperature as soon as possible. From a cold start they will run the ICE for longer to warm it up, rather than continually stop starting.      Cabin heat is secondary.   There will be a bit of  a compromise,  They may  open the thermostat a bit earlier than is ideal  to put some heat into the radiator  to indirectly heat cabin air.   But its more efficient to use  the heated seats  initially.    Eventually the ICE will have enough excess heat that it needs to be cooled by the radiator anyway. . Rather than letting this go to waste its can now be used to heat cabin air. Until this happens  heated seats are a more efficient source of heating.
 
As others have said  climate control and other cold weather demands will also require  the engine to run more often because of a higher demand for recharging.    Thats on top of the extra run time  used to warm it up quickly  .  A double whammy.   

78C coolant temperature seems to be quite low compared to what conventional cars often ran in the past    .  But I think a lot of research has gone into  extracting the maximum efficiency from waste engine  heat and generated battery power . I wouldnt call it a design fault.  .

[Kremmen]

23° is a very high temperature if you're using the climate in "Auto"

A lot depends on your age. As you get older you feel the cold. I have mine set to Auto 22c in winter and it works just fine.

At my daughter's house she has her lounge at 19c to 20c and she feels cosy bit I find it cold. Years ago when my parents visited me it was just the same, I was cosy but they complained of being cold.

[Zaier]

23° is a very high temperature if you're using the climate in "Auto"

A lot depends on your age. As you get older you feel the cold. I have mine set to Auto 22c in winter and it works just fine.

At my daughter's house she has her lounge at 19c to 20c and she feels cosy bit I find it cold. Years ago when my parents visited me it was just the same, I was cosy but they complained of being cold.

Yes I know about that but my wife still doesn't want to increase the temperature in the Jazz, which made me think it was warm enough.