Why changing engine coolant more often than factory recommendation matters

Agree. Which is why I have done ten coolant changes over the years.

 

Then why aren't more cars affected by them?
Corollas especially used the same 2ZR-based engine and there were twice as many of them sold, AND their head gasket failure rates are not even close to those of the 'turd-gen' Priuses.
Same head gasket.
Same coolant.
Same maintenance periodicities.

I completely agree with the FACT that Toyota's "lifetime" fluid change periodicities are only meant to last the 'lifetime' of their OEM warranty period.
It's also true that their coolant will break down over time and can damage gasket material.

 

Thermal cycling of the Prius

 

"I completely agree with the FACT that Toyota's "lifetime" fluid change periodicities are only meant to last the 'lifetime' of their OEM warranty period. It's also true that their coolant will break down over time and can damage gasket material."

There is truth, evidence, and some common sense in that comment

Green coolant used to be flush every 3 years. Red (Dexcool) 5 years - as I recall.
FWIW I would be inclined to 5 years flushes on Priuses.

PS I advocate distilled water instead of potable/ drinkable water to mix the coolant.

 

Old coolant, thermal cycling, never that carbon-choked mess that used to recirculate partially-cooled, evenly-distributed exhaust gas to the combustion chambers.

 

Wait, are you thinking your EGR theory is mentioned inadequately often on PriusChat?

 

You forgot oil-laden.....

 

Oldie but goodie.

 

I'm calling BS... My friends who changed coolant more often than others still had headgasket failures just as often. However people who had problems with electric pump for the engine coolant and went too long with a clogged EGR definitely had higher headgasket failure rates.

 

A simple litmus test of the coolant should tell the story; assuming the coolant wasn't recently changed because other work was done trying to fix the issue - before they brought it to you.

A guy in the UK had corrosion issues that jammed up his EGR valve on an early gen4. He was around 300K miles and admitted he never changed his coolant. His diagnostic code did point directly at that electronic EGR control valve.

YMMV

 

Do you remember what the diagnostic code was?

As far as I know, the gen 4 EGR valve is much like gen 3's, a stepper motor actuator with no position feedback. You can get the P0403 code if the electrical connection to the valve motor is detectably open or shorted, which would not be a symptom of corrosion jamming the valve. The more likely code would be P0401, which tells that the intake manifold pressure did not change by enough during a self-test trying to open and close the valve. So a valve jammed up by corrosion could give you that code, but so does anything that stops the pressure from changing enough when the valve opens, such as cooler clogging. There isn't any code I know of that points directly at the valve as the culprit.

 

No it was 12-18 months ago and his main complaint was hesitation upon acceleration if I remember correctly. The hesitation was pretty consistent from lower to higher RPMs and he already changed coils and plugs.

 

One of several cooling system changes on gen4 engines was an egr valve with coolant passages.


Other changes included grill shutters, cylinder wall insulators, a coolant flow selector (shutdown) valve and improved head gasket, block and intake geometry. The egr gasses were taken after the cat rather than before and the egr cooler was larger.

 

Yep; the reason I remembered it, he posted pictures. There was white (maybe calcium deposits) jamming the valve not black carbon. That's why I asked if he ever changed his coolant.

 

I think I remember noticing coolant nipples added to the Prius c EGR valve also.

While it suggests Toyota decided at some point they'd like to keep the valve a bit cooler, I would be very surprised if the passages offer any way at all for coolant to get near the moving parts. My bet would be it just flows in passages of its own through the aluminum body of the valve.

 

Sorry guys, it was the coolant bypass valve... Old-timers, not as sharp as I used to be...
Car is Juddering / Jerking during acceleration… | PriusChat

 

High (>7) pH solutions are alkaline, not not acidic. Good coolant pH should be in the 8-9 vicinity. You're correct that acidic (<7) coolant is BAD news.
Are you checking your coolant pH?
When my car had a little over 100k miles on the (I assume) original coolant, litmus paper showed pH I couldn't distinguish from the color I got with new coolant. Out of an abundance of caution, I had it changed anyway.