Error Code P0303 After Oil Change

ouch, sorry!

 

That was obvious from your symptoms. Now it's so clear a blind man could see it.

The question is how long do you want to drive it? Dump the car as is? Quick flip to pass on the hot potato? Low cost replacement JDM with some small risk? Or a top quality rebuilt that will go 150,000 miles?

Also factor in that hybrid battery.

 

Hopefully the previous owner didn't dump a 'stop leak' product into the coolant. If they did a used motor is just the beginning of your repair journey.

 

Releasing the pressure reduces the amount of coolant pushed into the cylinder as the engine cools off. Reduced loss of coolant means you will drive it with a leaking hg longer and will likely do more damage. Nothing is fixed, the cooling system will allow engine temperatures to rise beyond normal and most people will think everything is great until it seriously overheats and strands you.

Your engine already blew the gasket once per your seller; it's either still blown because he used stop leak which wore off or it was poorly repaired and blew again.

 

Your head gasket issue is still there. It's just easier for gases to leak through than coolant right now. Some people remove the sealing o-ring on the coolant bottle to prevent pressurization. When you turn off the motor, the pressurized coolant seeps into the combustion chamber - it can't do that with the motor running - ego the engine stumbles when started then goes away.
You need to monitor your coolant temperature. Chances are the motor is running hot, just not hot enough to trip the over temp.lamp yet. Normal operating temperature is 190-210F max., over temp lamp goes on around 248F

 

The attached TSB has part nos for Toyota engine rebuild gasket kit, and the head bolts as well.

Note, the kit includes Toyota’s head gasket, which I believe has been revised.

There’s a popular sentiment that Toyota’s head gasket was “defective”. While it may be partially the case, I suspect the clogged EGR system is the main contributor to head gasket failure, and is tough on ANY head gasket brand.

Wouldn’t hurt, and only about $10 USD. Attached is a repair manual link for PCV valve replacement. I’ve used a locally available, non-permanent, oil-tolerant thread-lock on the threads (vs the repair manual specd): Permatex Threadlock Blue, surface-intolerant.

I suspect it’s not strictly necessary to apply anything to the threads, but it does prevent oil-bloom, I found.

I think too, a new one will have Toyota spec thread sealant pre-applied, so…

Yes, repair manual (and various YouTube videos) say to oil-soak them.

repair manual spec for the head bolt “socket” is “10mm double-hex”. A lot of YouTubers advocate a “triple-square”, but that is not optimum. The double hex is readily available. One option: “CTA Tools 9292”.

Shouldn’t be necessary. Specs are in repair manual.

the form-in-place gasket that Gasket Masters use (in your linked video, looks a suitable and readily available alternative to Toyota spec, and likely better for DIY, due to much more leisurely cure time.

the last link in my signature is the full engine section from repair manual. (On a phone turn it landscape to see signatures).

also linked in my signature, the first EGR related link had repair manual excerpts with info on intake manifold and EGR removal/install, with tips and torque values.

lastly, indispensable: the @NutzAboutBolts video link thread has numerous related videos, including recently added head gasket replacement. (It’s pinned at top of 3rd gen maintenance forum).