Did Toyota botch my head gasket job? (coolant temps)

I noticed some "different than usual" behavior with my Prius' coolant temps.

In reference to this thread: Coolant Temp: 200 to 195 quick... | PriusChat

My Prius usually operates spot on at 186-188F when driving (like religiously spot on), even accelerating up hills (but I never go over 3000rpm). It pretty much never went over this. I monitor coolant temp constantly with my scan gauge since I bought the car 4 years ago.

I replaced my thermostat and water pump with new Toyota units, and still normal 186-188F. About 12k miles later, my head gasket blew.

After having my head gasket replaced by Toyota, I noticed on 90-95F days, my temp will climb to 201F, sometimes (when staying under 3k rpm). A couple times to 205F for a few min. My car never did this before the head gasket.

During this behavior, If I turn the heater on max heat and fan, my temp drops (and stays) back to my normal 186-188F, even at 2500rpm on the highway. It never behaved like this before my head gasket, which is concerning to me that somehow Toyota messed up the head gasket job. I'm not sure they if machined the head/ checked for flatness, this is about the only thing I can think of they would mess up.

On cooler days, like 70-80F, it stays at my normal 186-188F.

If there were air bubbles in my coolant, I would expect to see temp fluctuations at any ambient temperature. I've had this before on my Honda, and the temp jumps right away. I still have yet to check this.

I'm not loosing any coolant. And no knock/rattle on starts.

About the only thing I think it could be is an issue with the radiator, but my radiator looks fine. No bent fins, that I can see.

Any thoughts?

 

No sealant was used.

I read whatever temperature scan gauges reading, I assume the one in the block?

I'm mostly curious why the temperature fluctuates and increases now, when it never did before and does not increase when I have the heater on helping to dissipate heat.

 

EGR system is fine.
At 216,529mi, intake manifold replaced with brand new updated Toyota p/n 17120-37054 per TSB T-SB-0010-12.
At 216,900mi, EGR cooler and valve both replaced with new Toyota units. Old EGR cooler had 60k miles on it and you could still see through it when removed.

At 232,860mi - Water pump and thermostat replaced with new Toyota units. Just as preventative maintenance, no issues present.

At 245,726mi,
End of February, head gasket let go unexpectedly and instantly on my normal 36 mile drive home from work. No check engine codes ever came up.
Nearly home, I stopped for gas, checked oil and coolant levels just to do so (both spot on). Drive away normally, hit two lights and and three stop sign. 5 min later at the next stop light 1 mile from my home, I start accelerating gently and loud "thud thud thud" and car shook for a second, then starts driving normal. Same thing at the next stop light, about 50 yards away. I knew immediately what it was. Luckily, I was able to limp it home in EV mode. Again, no CELs.

I pulled the plugs and used my borescope camera. Interestingly enough, it looked as though my gasket gave out between cyl2 & cyl3.

I specifically instructed Toyota check piston to deck heights to try and spot any bent rods. Luckily, they said the heights were spot on. I forgot to ask them to/if they did machine the head, though (doh!).

Currently at 252,500 mi. Car has burned zero oil or coolant since I got it back.
It's been driving/does drive fine, I just noticed this issue and it's just different from what I've experienced as "normal" operation before the head gasket.

I should note - the head gasket let go the end of February, winter in the midwest. I got the car back early March, so right as ambient temps were starting to warm up.

 

Oil catch can installed at 164k. Intake manifold partially cleaned at 173k, then fully cleaned at 177k using throttle body cleaner (WAY better than brake cleaner). I usually checked and removed any accumulated oil out of the bottom of the manifold about every 5k or so miles.

I removed the oil catch can at 216k when I changed the intake manifold, as I personally found it to be more headache than help (being in the upper Midwest). I would have to drain it every day in the winter to prevent carry-over due to the temperature change from cold to hot and so on causing condensation in it along with catching the oil. I've been fine, since, and do still monitor and maintain the oil in the manifold. It seems somewhat less with the updated gasket design, but that's my subjective opinion. Not a single engine knock since I change it.

Close. EGR valve and components cleaned and cooler replaced at 159k w/ new Toyota.

I purchased the car at 153k, so I'm not sure if it was done before my ownership (doubt it), even though I have the majority of the maintenance history since it was new. Religious oil changes every 5k miles until my ownership when I switched to 7500 mile intervals. Always Mobil1 extended performance high mileage and Mobil1 filter. The engine has been perfect the entire time I've owned the car.

Mine failed suddenly. No warning signs, No overheating issues before hand, no coolant loss, no exhaust smoke, no engine rattles on start up, no misfire codes, no check engine lights before/after, nothing. I've monitored the water temp with my scan-gauge since 153k miles, when I purchased it. Which is why I make this thread about the fluctuating coolant temps. My car has never done this prior, at least not going anything over 190F.

I DO think at some point I had been driving on borrowed time, though. I DID randomly have about 3 times (all randomly and spaced a good amount apart) of cold engine rattle start ups when left sitting undriven for an extended period of time (like 1.5-2 weeks). So it was probably extremely slowly starting to leak, condensing into the cylinders in those cases. But, again, the entire time until the head gasket completely failed, I never lost a drop of coolant (at least not enough to register "low" on the reservoir and needed to add) and never burned a drop of oil. It's been a reliable little car

I also don't take the RPMs over 3000, like 98% of the time. Most of my driving is like 75% hwy. So this probably helped extend the failure, too.

I agree with you, here. Though in my experience, I personally think 50k is a little early, with how good my cooler looked at the 60k interval mark. The carbon was not completely caked onto the inner fins and it was pretty minimal. It's better to play it safe, though.

In my case, I truly believe the EGR system was a non-issue contributing to the head gasket failure, and I was probably driving on borrowed time starting at some point. Again, my head gasket failed between cyl2 & cyl3, not cyl1, which would be the first intake manifold port to clog, as you state. Perhaps lack of maintenance prior to my ownership could have affected it in a way that was so minute it was a non-issue? Who knows.

 

I determined the problem. It seemed like the car was acting as if the radiator was not getting enough airflow.

After some hypothesizing, I examined the front grill screen I installed behind the bumper grill to prevent bugs and rocks from hitting the a/c condenser on my 35 mile (country road) commute. It was somewhat littered with dead bugs. I sprayed it off and the temps got just a tad better, but only a tad.

Then, it hit me: the grill screen openings were probably too small, effectively acting like a semi-blocked grill. This was the root cause.

Testing my theory, I bought new grill screen with openings that are twice as big as what I had. Problem solved. I'm back to being spot-on at 186-188F.

Why this issue decided to pop up all of the sudden is beyond me. I've had the screen installed since 2021 and didn't have any issues (except the one time in winter when wet snow blocked it). Maybe we didn't have as many super hot days over 95F, as we have this summer? I don't know.