Head gasket diagnosis

A rattle means the engine misfired. There can be lots of reasons for that, so I'd be inclined to back the question up to "why did it misfire", and let the answer take me to the gasket if that's where it takes me.

Even the members most likely to jump on any reported rattle as a sign of head gasket doom usually seem to agree that cylinders 1 or 2 are where that doom typically starts. Your misfires being in 3 and 4 might offer even more reason to take a deep breath and pursue the incident as misfiring, cause not yet determined.

 

Head gasket failure on 3rd Gen (and v) usually starts with coolant leaking into cylinders. That tester detects carbon monoxide in coolant, which I would speculate happens later, if at all. Try boroscope inspection first thing in the morning, looking for pooling coolant atop pistons.

 

Any car nuts nearby?

There's a guy second house up the block from us, with a lift, and might have engine stand as well. I try to stay in touch with him, in case I need to borrow them someday, and that day may never come...

 

It won't be long now

 

No I doubt you'll be doing the in the car nonsense because everything is starting to show decent wear now these engines have no meat on them there's nothing to machine once things starts getting scratched and all of this and that is just better to replace the reciprocating mass which is in the middle of the motor essentially You can buy all that built up from Toyota about 1600 You might even consider the generation 4 engine pieces or center section it may bolt right up to all the Gen 3 stuff or it should I can't guarantee that's going to be a whole lot better but at this kind of mileage on your car you certainly can't be trying to keep a generation 3 that long but maybe it's kind of planned to be disposed of and relatively short order 8 years or something seemingly all the ones I see are generally ready at about that time

 

I'm not convinced that your have head gasket issue, have you checked for coolant loss?

when was the spark plugs last changed since there's 160K miles on the clock?

And have the EGR Circuit every been cleaned? A clogged system could cause miss fire...

Posted via the PriusChat mobile app.

 

Just pulled the plugs about an hour after a decent run on a nice hot day like we're having all over the country now unless you live somewhere very different when you do this all you're looking for on the insulation insulator portion of your plug the part that's inside of the combustion chamber you're looking for little tiny water droplets and smell each of those tips of those plugs you're looking for the smell of coolant lick your finger touch the plug touch your tongue If you don't know what coolant tastes like well I don't know what to say it's very distinct That's what you're looking for It will probably be there in cyl 1 or 2 . But you need to check them all and use a magnifying glass to look very carefully at the tips of the plugs once you see the moisture drops there you go now drop a camera down in there look back up at the gasket surface see the droplets hanging around the gasket surface mating points then when you take it apart you'll get a better look at all this and see how it took the three or five layer gasket right out

 

Cylinder 4 looks steam cleaned. They should all look like 1 and 2.

Coolant gas, coolant in oil, compression and leak down tests will all fail to detect an early Prius hg leak that seals itself up in seconds and will be clear for the rest of the day. Many times no codes. Often nothing for days or weeks. Many spend $1000 just shotgunning plugs, coils, injectors along with egr cleanings with no lasting results. Borescope and occasional symptoms are THE early diagnostic tool and most “good” mechanics don’t know this on a thermally cycling clutch dampered gen3 Prius.

By the way, minor one second non-metallic stumbling on some startups is normal and is often not observed until the driver becomes hyper vigilant after the first severe multi second rattle.

I suspect your $1000 quote may be cutting corners on this hg job unless he is cutting you a great deal. Timing chain reassembly errors are too common as are timing chain cover leaks. But those factors are usually diy errors.

Rebuilt with Toyota revised pistons, rings and egr firmware is a better solution with head inspection and rebuild if needed by a machine shop.

While removed the shop should perform a complete intake and egr system cleaning including the cooler. Ask the good mechanic if his price includes the head inspection/rebuild by a machine shop and the egr/intake cleanings, which can be $500 and $800 respectively at many shops.

For reference, Toyota revised pistons, rings, head gasket, intake and egr valve along with updated ecm software on these cars trying to resolve oil burning and hg failures.

Classic Gasketmasters “should I wait” hg video - late stage for coolant loss and holes in the block. The severe startup noise and shaking is any stage with early stages being occasional.

 

I would also hesitate to call it a head gasket just yet. It's highly suspect, but it's weird that'd be cylinders 3 and 4 and I'd think you see at least a little wetness. I got serious cold start shakes about 4 times randomly in the 5 years I had my car before the head gasket blew so it's not always the head gasket. If you get more shakes then I'd borescope the cylinders again after it sits for a while, looking for wetness. That being said $1000 + parts is a good deal. New short block or pistons and rings would be great but so would not spending a ton of money. If you caught it early enough your block surfaces might be fine. I've been burning more oil than that for 100k miles.

As also mentioned, if you don't continue getting cold start shakes the EGR system could be a suspect. If cylinder 1 or 2 intake manifold runners get clogged it can cause issues with cylinders 3 and 4. That's happened on my car and it caused minor stumbling on light engine loads.

Do you have a photo of the spark plugs with what cylinder they came from? If the plugs from 3 and 4 were dark I'd be thinking clogged intake, if they're clean I'd be thinking head gasket.

 

Wetness is only viewed under specific conditions. Cold engine which opens the hg leak. Under coolant system pressure which can be pumped up manually. By using a top quality dual view borescope.

video on another Toyota engine
Car Care Nut HG Borescope at 7:40

 

EGR will be reduced and too hot.