Concerns about momentary spikes in Engine Coolant Temperature

Well I would first check if you have the right coolant level. When the car is cool, open the radiator cap and fill as needed

 

When I had this problem with my 2007 a year ago it was simply air in the system. Hopefully your problem gets resolved that way. But in general I think you're being overly-vigilant about these relatively normal number and as the saying goes: A watched pot doesn't boil.

 

That is a reasonable hypothesis, with the added benefit that it can be checked. The OP should verify that when the car is totally cold (like after sitting overnight) that the coolant is up to the top of the fill tube and that the level in the overflow tank is at the center. If either is not correct, then there is air in they system. Refill to the tube top and/or overflow center, and repeat daily until the levels stop changing. If they never stop being low then there is a leak somewhere.

There are some other possibilities but they all seem pretty unlikely.

The temperature measurement could occasionally be faulty, from a loose connector, or some timing issue in the relevant computer.

The thermostat might stick closed briefly and only occasionally. (Really unlikely since since it would normally open at 87C (185F).)

Some sort of chunky contaminant might be in the coolant which temporarily blocks the coolant path, when it releases the overheated coolant from the motor might appear as a spike.

 

That's exactly what I did to fix it...

 

Wouldn't hurt to sniff the radiator for combustion gasses

 

I suggest driving the car to get the ICE warm, then park on a level surface- parking brake applied. Do a quick check- turn on the A/C- do the radiator - condenser fans both work? If they do then continue.

Turn off electrical loads (lights, heater, A/C). If the HV battery is less than 6-7 bars then force charge it. Next, press on the brake and gas pedals at the same time- the ICE should run. Shift to neutral and the ICE should stay running at about 1000rpm. Release the pedals. Now monitor coolant temperature and see how high it goes before the radiator fans come on. Keep an eye on the HV battery level as the car can't charge in neutral.

The service manual shows that fans should turn on "above 199°F" - that's for low speed. (Compared to many cars that's a very low temperature. 210-220° is fairly common). If the fans work properly then any temperature reading that consistently stays below the "fans on" level should be fine.

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