Winter Operation

91°C (195°F) is the normal operating high.

When the temperature outside drops, it's more of a challenge reaching that. So, we block the grille to help reduce the loss of heat.

 

I will admit that I've never see an official document that outlines the maximum coolant temperature for the Prius engine. Hopefully, someone can link an official source. I have seen the coolant temperature as high as 198F (92C) during extended hill climbs in the summer when the OAT was 102F(39C). I think the car will take care of itself as long as you don't impede airflow while operating it as outlined in the owners manual.

Now regarding cold weather... Living on the west side of the Cascades, I block the lower grill 100% when the high temps are consistently below 60F(15C). The engine seems to reach 103F (39C) within the first 1/2 mile (>160F/71C by 1.5 miles) with temps in the low 40's on surface streets with speed limit of 35mph or less. The engine does seem to retain heat better without having to restart itself to warm up during city/slow EV driving.

 

The car tries to get to 195F (91C) as a matter of course. I have seen 198F (92C) as my max temp.

 

AFAIK grill blocking doesn't affect the warm up time, the thermostat stems the flow through the radiator until the engine is up to temperature. Grill blocking will help maintain the heat once its up there.
On a different note, one thing that I've always wondered about is, does engine braking cool the engine on a petrol car ?
I would think it does on a diesel engine as there is no throttle plate so it's drawing in fresh air through the air intake, but on a VVT petrol engine does it even draw in any air ?

 

Actually, engine braking on a big diesel retains heat rather than cooling it. Sudden gulps of cool air are bad for red-hot pistons in a diesel. The diesel engine brake closes the intake valves and just cracks open the exhaust valve, retaining heat. I'm not sure what the ICE in the Prius does with the valves, but it does alter valve timing. In either case I doubt it offers any "cooling".

 

Thank for the info, logically it makes more sense to close the valves, it sort of holds the pistons back more on the suck and squeeze strokes.

 

Thought I'd weigh in regarding blocking the radiator: I'm in Saskatchewan and we had more than a week where the temperature didn't get any warmer than -27C (coldest was -35C). I did plug in the block heater, but aside from that I didn't do anything else and it had no trouble pumping heat inside (this is a 2014 Prius V).