Join Date: Mar 2011
Location: Mid Hudson Valley, NY (USA)
Re: Toyota Sienna Radiator pressure
The dash gauge is a rough indicator of 'normal' - it's dampened quite a bit and doesn't indicate small changes in actual temperature. It will hold steady with an engine temperature of around 185 to 215, and then start to rise if the system temperature exceeds this. For a more accurate reading you can use the OBD port and one of the better laptop or smartphone apps to read out real time the temperature sender.
This assumes, of course, that the temperature sender is accurate, and outputting valid data. And that your thermostat is opening and allowing the hottest water to circulate. And that the coolant level is right (the system is full) so that sensor is fully submerged in the hottest water. Lots of dependencies....
As the temperature rises, so does the system pressure. If your pressure cap is working right, it should be releasing at just above one atmosphere (1.1 ATM, or around 15 lbs). Assuming the cap is working, if you don't see the overflow bottle filling fast, the system is not over the specified pressure.
Current: '15 Sienna Limited Premium (FWD), '14 Subaru Outback, '13 Honda CRV AWD.
Past: '08 Sienna LE (FWD), '02 Subaru Outback, '02 Honda Odyssey EX