New to the Prius (just bought a 2006 package 4) and have hooked up my scangauge II to the system and made some observations while driving. My understanding of the Prius engine coolant system is that hot coolant is stored in the "thermos" to speed warm up and it is reportedly able to keep coolant hot for days. My experience with my Prius suggests that fWT as reported by the scangauge does not stay very warm. For example, if I drive to work and turn off the car with fWT reported at 170F at ambient of 60F, I can come back in 8 hours and start the car with fWT at 70F and warm up is not significantly speeded by my eye by any injection of hot coolant from the thermos. Is this typical? I can see about getting an actual data log rather than "eyeball" data. Is there a way to monitor thermos temp with the scangauge? My reading of the various diagrams suggests there is not a temp sender in the thermos. My concern is that my thermos is not functional. Is there a way to verify performance of this system beyond touching the thermos to see if it is hot (vacuum failure)? Thanks for the great info and expertise present on this forum! -Jon
Congrats on your purchase. Your experience is correct as far as you have observed. The Prius is a cool running vehicle and does cool down fairly quickly. The thermos will not keep coolant hot for very long. The purpose of the thermos is to pre-heat the cylinder head for emission purposes. What you can do to check the thermos is to make sure your Prius is warmed up before shut-down. After 8 hours, start the car and watch the scangage during the 8 seconds before the engine starts. You should see the temp go up as the thermos injects into the heads. Then when the engine starts, you should see a slight dip before it rises again. This works best when the temp is cooler outside. Wayne
The coolant, even if kept perfectly hot in the thermos, is going to cool down quickly when pumped into an engine at ambient temperature. The engine is far heavier and has a much higher heat capacity than the coolant in the thermos. I don't imagine the thermos is really all that effective in doing anything much except in making potential buyers think it's a neat idea.
jengel, If it hasn't been said already, :welcome: to PRIUSchat. There are many systems -- maybe even all of them! -- in the Prius that operate diferently than in conventional vehicles. Here is a good place to go for the low down on how the various Prius systems operate: Autoshop101 - Automotive Technical Articles If you go to the section, Hybrid04 Engine, you'll find a discussion of the ICE cooling system. I've posted a link to the index page, because I'm sure that you'lll find other things to delve into... the fuel and evap system is a real doozy!
That is a good point. The engine/transaxle assy is a hefty heat sink, along with all the fluids therein. I wonder what the estimated efficiency/pollution gain was by the engineers at Toyota to include such a complicated coolant system. Then what is the real-world impact? Anyone running without the thermos out there care to chime in? -Jon
170F is not enough to store the coolant. John's Stuff - Toyota Prius - 2004 Tech Presentation 40 "Start condition: engine coolant temp. reaches 85C (185F) or more" Ken@Japan
