Prius Hybrid Cooling System Explained | How Prius Transaxle Inverter Coolant Loop Works | Gen II

The inverter cooling system is completely independent of the ICE (Internal Combustion Engine) cooling system. It uses a separate radiator and water pump, and it operates at a lower temperature than the ICE cooling system. Here are the #ᴬᴰlinks to tools, parts and accessories you may need to perform this repair:

1. https://amzn.to/3ZGnHCu | Coolant Control Valve fits for Toyota Prius Coolant Flow Control Valve 2004 2005 2006 2007 2008 2009 4Cyl 1.5L Heater Control Water Valve,16670-21010 601-021
2. https://amzn.to/41nywdW | Zerex Asian Vehicle Red Silicate and Borate Free 50/50 Prediluted Ready-to-Use Antifreeze/Coolant
3. https://amzn.to/3D4LOCa | G9020-47031 Engine Electric Inverter Cooler Water Pump Assembly for 2004-2009 Toyota Prius 1.5L

Or Click on Amazon link here and search for what you need: https://amzn.to/3D1T2GQ

The Prius transaxle system, with its use of heavy-duty motor/generator units, is no exception to this rule. Temperatures get so hot under the hood that the vehicle requires a dedicated cooling system to prevent catastrophic damage to the stator windings. This is where the inverter coolant loop comes into the picture. It functions separately from the engine cooling system, though they both use the same type of compound to control operating temperatures.

The inverter loop includes a brushless 12V electric pump to circulate coolant through the baffles of the Prius transaxle. This fluid absorbs heat from the inverters, then flows past the engine’s electronics, cooling them in the process. It releases heat to the surrounding air as it passes through the vehicle’s radiator, then returns to the bafflers for the next cooling cycle.

While this may sound identical to how a conventional engine cooling system works, there are important differences between the two. The inverter cooling loop does not have a thermostat, for example. Also, it keeps the coolant at lower pressures than its counterpart.

The Prius uses an independent cooling system to keep the inverter and motor/generator (M/G) at a safe temperature. In warm weather, problems with the inverter cooling system are fairly common in both the Gen 1 Prius (2001-2003), and Gen 2 Prius (2004-2009). The inverter cooling system uses the same type of coolant as the ICE cooling system. Gen 2 was factory filled with Toyota Super Long Life Coolant (SLLC). SLLC is premixed, eliminating the hassle of mixing and the potential for error.

Servicing the Inverter Coolant Loop

While some object to the complexity of its layout, in truth, this supplementary cooling loop does a good job of protecting the Prius transaxle from heat damage. Of course, nothing lasts forever, and these systems eventually develop a host of problems. Typical issues include:

Air pockets forming in the system: These can be removed by using the built-in bleeder system to flush out old coolant, but fixing the underlying problem means replacing defective components.
Pump failure: This can be diagnosed either by removing the cap of the expansion tank and checking for circulating fluid or by touching the pump housing while the Prius is running. If it fails to vibrate, then the pump is not working. Some Toyota pumps have shown sub-par performance over the years; check the service updates for the particular vehicle you’re working on.

Low fluid levels or use of non-standard coolant mixtures: Toyota is very clear that only its formulas should be used for cooling the Prius transaxle. Unfortunately, the desire to save a buck or two means that some owners or shops use inferior products. When this happens, the results can range from poor heat control to outright vehicle damage.

Here's the complete playlist of our Prius' videos:    • Toyota Prius Auto Repair & DIY How-To...  

Thanks for watching, please check our other DIY auto repair tutorial & guide videos on EyeOnAiman's channel. Other cars Aiman have worked on includes Honda Accord, Civic, Insight, CR-V, Hyundai Santa Fe, Elantra and Toyota Prius Hybrid.

Obviously, Aiman's auto repair videos are mostly designed for entertainment purposes. Aiman is not a professional and not a certified ASE mechanic. The videos should always be used only as a guide.

You can watch all of Aiman's auto repair videos in the following playlist:    • How To Remove Alternator Hyundai Sona...  

This video is presented to you by Aiman-Imran Anuar. You can watch more of#Gen2Prius and #Aiman_DIY_Auto_Repair videos on #EyeOnAiman Youtube Channel & Facebook Page.

Note: This video is NOT sponsored. Some product links are affiliate links which means if you buy something we'll receive a small commission. As an Amazon Associate we earn from qualifying purchases.

Recording Date: November 28, 2018
Video URL:    • Prius Hybrid Cooling System Explained...