What am I missing? Head gasket Dx

it's a super tiny leak that's difficult to view with even a really good camera... But the rough running and coolant loss is enough of a symptom for this known problem. Also without knowing the fixes the mechanic tried, it would be difficult to figure out what they meant by that.

 

If the mechanic did indeed do the head gasket job - the leak would be visually apparent on either side of the head gasket for confirmation. If it isn't, the problem wasn't the head gasket and he misdiagnosed it. You think the mechanic would take that hit and work for free???

Just my two cents...

 

The head gasket used is a Multi-Layer Steel gasket with a black coating. They depend on very flat machined surfaces. Severe and prolonged overheating can cause a head gasket fail on a gen3 or any modern aluminum engine. Severe overheating typically causes a warped head.

However the "normal" gen3 Prius head gasket leak does not require overheating. Most of them never overheat before early onset hg symptoms. The symptoms are severe cold start rattles that clear quickly and may not repeat for weeks or months. They pass combustion gas tests and generally produce no codes since it runs fine after the first few seconds. Mechanics are often confounded by these symptoms and suggest a thousand dollars worth of plugs, coils and injectors, usually a piece at a time. With no success.

Typically the steel hg black coating has eroded between the cylinder and a coolant passage. Acidic coolant and carbon based pinging is the most likely cause along with poor gen3 head geometry and a minimal amount of black coating.

With the gen4 1.8L engine Toyota updated the head gasket, head geometry, and rings to reduce oil burning (another common issue), along with improved cylinder cooling, egr design and more.

What can diagnose an early gen3 hg leak is a dual view borescope inspection with a cold engine combined with a pressurized cooling system. There are several videos routinely posted here showing the process. Failure to act quickly to early symptoms can eventual progress to traditional hg problems including a warped head, bent connecting rod or hole in the block.

 

I *don't* know that, and seeing you already so seemingly fixated on that possibility, in a car apparently using no coolant and having started a little rough maybe twice recently, makes me worry that you (not your car, you) are a casualty of the sort of totalizing way it gets talked about here.

 

Caring too much about your vehicle running well can create alotta stress. However the amount of cars I work on where people are the opposite of caring for their vehicle and expect me to repair what's created through their own negligence is so much worse! Especially when I'm trying to save people from how much local mechanics, as well as Toyota Stealerships charge.

 

This puzzles me. Seems a rare event indeed, that someone with a gen 3 “presents”, saying “all I’ve ever done is what the dealership recommended”, it’s got 200k miles, and engine’s running fine.

 

Coolant needs to be changed on OEM intervals because they go acidic and eat away at your seals and gaskets from the inside out. That's something that always get overlooked in southern cars, because people say it doesn't freeze here. It's basic chemistry; ask any boiler plant operators; not a lot of them left now-a-days.

 

it's not a mythical issue, but it can be a confusing one, thanks to toyota basically ignoring it.

and we get in these arguments every time, because no one knows for sure what causes it, or there may be multiple causes

 

Multiple factors when combined and aged create the hg problem. Low tension rings and long duration fluid changes are certainly on that list. Buying used has many unknowns especially when carfaxs are incomplete.

There are also examples of gen3s that make 250k - 350k without a hg fail. However those are few while other flaws can and do junk the cars much earlier.

 

I suspect that because these failures usually happen after 150K miles they consider them to be an issue at the end of the lifespan of the vehicle and the legendary ability for Toyota to go way past 300K miles without issue is seen by them as losing money on not selling new cars.

 

until i joined priuschat, i had no idea that people expected cars to run for hundreds of thousands of miles without any major repairs.
when the hg blew on our 80k miles windstar, i just figured i was unfortunate

 

Toyota Trucks started it... But these days engines burn so clean if you drive alot it's fairly common. Not many of us remember the days when auto shops were competing to sell "Ring and Valve Jobs" at a batter price than other shops and this was before a car hit 100K miles.

And some of the old junk cars when I worked at an auto shop in high school literally had a 1/4" thick layer of grime coating the entire inside of the engine, especially under the valve cover.

 

toyotas build quality is probably still near the top of the food chain, but the hunter for higher efficiency from gas engines may be biting them

 

I think gen3 suffered from management wanting more power, more mpg and advanced safety tech without the expensive testing and high dollar catalytic converters gen2s employed.

With updated software and parts the 2016-2021 Prius +/alphas/v's became a reliable vehicle worldwide - especially in taxi fleets where an engine swap was no big deal if the overall platform made 400k-500k.