Prius 2010 1.8 cooling fans not coming on when car hot.

[Dr Gunsmith]

Hi, information needed, Iv noticed both my front engine fans are not kicking in when she warms up, any ideas or places to start checking why, had to change the thermostat and coolant water pump also changed the engine coolant censer, put her in maintenance mode and let her run with the coolant cap off to burp and get any air bubbles out, everything seems to fitted correctly, but I let the engine run in maintenance mode for about 30 minutes and heat/steam was coming out of the coolant fill bottle with cap off, but the fans did not come on at all, hope this makes sense, so not sure what I need to do,  sorry if I don’t use the correct terminology as I’m new to all this, also new to Toyota Prius. Thanks.

[TonyHSD]

Hi, 

if you have coolant boiling in the expansion tank and radiator fans off may be because of a stuck thermostat in closed position and the coolant not able to run through radiator. Have you checked the radiator was getting hot too with both hoses up and down hot and the hose after the thermostat hot? It has happened to me previously and it turned to be the thermostat faulty even brand new out of the box. Bought a blueprint thermostat which was oem actually and all sorted. I also did boiled all thermostat in hot water to see which one opens and which one not. Other than that another reason can be air locked inside the system, I think you have an air bleeding valve somewhere on top and behind engine, white cap on black hose, but not all models has got one.  👍

[Dr Gunsmith]

On 11/11/2021 at 6:19 PM, TonyHSD said:

Hi, 

if you have coolant boiling in the expansion tank and radiator fans off may be because of a stuck thermostat in closed position and the coolant not able to run through radiator. Have you checked the radiator was getting hot too with both hoses up and down hot and the hose after the thermostat hot? It has happened to me previously and it turned to be the thermostat faulty even brand new out of the box. Bought a blueprint thermostat which was oem actually and all sorted. I also did boiled all thermostat in hot water to see which one opens and which one not. Other than that another reason can be air locked inside the system, I think you have an air bleeding valve somewhere on top and behind engine, white cap on black hose, but not all models has got one.  👍

Thanks for the information, Iv now sorted the problem, it was a extremely cold day and once I left her longer, for about 20 minutes they kicked in. But thanks for the pics.