Weird Temperature Issue

[timjamz]

Howdy, all! I'm a new Yaris owner but long-time Corolla, Camry, 4-Runner, Sequoia owner and DIY repair person.

My scenario: Just bought a 2007 base sedan, manual transmission. The temperature "cool" light comes on at cold start and goes off after a few minutes, as expected (I wish it had a normal gauge, but I digress). After driving for 20-30 minutes no "overheat" indicator (ambient outside temp around 70F). Seems to operate just fine. I have replaced the red coolant and thermostat with jiggle valve at 12-o'clock (along with oil, gear oil, brake flush, etc being a new purchase).

My question: Is it normal on this vehicle (1NZ-FE) for the lower radiator hose to remain cool to the touch and the front fan to never come on? The upper hose gets plenty warm, but not like scorching hot. Cabin heat gets normal hot. Squeezing upper and lower hoses sloshes the coolant around like normal (not hard as if there was a blockage). When re-filling coolant, plenty of air gets burped out like a normal drain & fill. I've ordered an Aisin water pump, thinking surely it must be on the way out, since the lower hose is cool and no fan triggered... is that a good guess, or does this motor just run super cool?

Thanks for any tips and feedback!

[WeeYari]

I must say that in the 18yrs that my '06 was operational I'd never felt the hoses so can't comment there. Also, in those 18yrs, I'd never once seen the fan activated.

[timjamz]

Thanks for that feedback! Still driving around with no issues, so maybe it just runs cool by nature. I'll be swapping out the water pump anyway, for some peace of mind since it's not too expensive. I will report back about hose temps after that change.

[mitch9521]

You've really gotta work a 1NZ-FE to get it to overheat, it runs so cool. Hell, unless my A/C is on(black car so its always on in the summer) my radiator fan never comes on.

[timjamz]

Thanks, Mitch. Outside temps here got up around 80 this week, and I did notice the lower hose warm then. I haven't swapped out the pump yet, but I'm definitely getting the impression this motor just runs cool by nature. I did have the belt off and felt no play in the pump or weird noises when it spins. :iono: I will update once I change out the pump.

[timjamz]

Well, I've replaced the thermostat and water pump now. Even after refilling the coolant and letting it bleed air for about 30 minutes, still the lower radiator hose is cool. Unless I'm doing something significantly wrong in draining/filling the coolant such that I've got a massive air pocket, I can only assume this motor just runs really cool under normal conditions.

:w00t: