Death rattle

Pull the plugs, look into the spark plug holes. If you have an inexpensive bore camera
you'll be able to see better. Do any of the pistons looke cleaner than the others?
Do you see any evidence of the head gasket leaking into the cylinders? Usually #'s 1 and 2.

 

what does putty do?

 

I hope he meant putty knife or spreader, used in testing to block EGR at a flange connection temporarily. Putty could cause trouble of its own.

 

Do you hear a sucking sound when you open up the coolant reservoir?

 

Try giving it a bottle of fuel treatment

 

I'm also currently trying to get rid of that dreaded rattle. I bought the car used in June 2022 and it ran fine for a couple of months and then the rattle started. Initially I thought the engine had blown up until I looked on youtube and saw a number of videos discussing the issue and then I discovered Priuschat. First thing I tried was changing the spark plugs and the rattling stopped for a few days but then resurfaced so I put in new coils and the rattling continued. Next I cleaned the intake manifold and replaced the pcv valve (I used brake cleaner and a pressure washer to clean the intake manifold as suggested in Merv's youtube vid) and it stopped for a day or two but then returned. Last weekend I removed and cleaned the EGR valve and cooler which ended up being about 6-8 hours due to never doing it before and it was just hot outside 94 degrees so I had to take some breaks. It seemed like it fixed it for about a day but the rattling returned. I keep checking the oil but there's no evidence of water. I just saw a video suggesting doing all of the above and then also trying to clean or replace the fuel injectors so today I removed them and used a small syringe, 3ml, the smallest Tractor Supply carried, removed the plunger from the syringe and attached a fuel hose that fit on the top of the injector and squeezed the other end of the hose into where the plunger went (got that idea from "Rally VW GTI KR" on youtube) and put the carb cleaner straw where a needle usually goes in the syringe and powered the injector with a 9v battery attached via alligator clips. I had to hold the hose onto the injector because it kept popping off anyway I used a whole bottle of carb cleaner and once I got everything back together it rattled briefly after startup but then ran smooth. Tomorrow morning when the engine is cold will be the true test to see if the fuel injector cleaning fixed the issue. I think the EGR and cooler cleaning is the most difficult just because of how hard it is to get some of the nuts and studs out and removing the coolant hoses and refilling the coolant. In my opinion after having done all of the above, I would probably start with spark plugs because I think they are fairly easy to change and inexpensive. Then try cleaning injectors, then intake manifold and then egr valve and cooler last. If the rattle continues after cleaning the injectors, I'll probably take it to a shop to see if they can check for head gasket issues or buy a kit to check for exhaust coming out of the radiator because I definitely don't see evidence of water in the oil but maybe prius' are different than other cars. I'd definitely want to try the things that don't cost money first but all of the things I did seemed to be needed.

 

DO NOT DRIVE IT !!!! Call Gasket Master, They will change the Gasket and swap EGR's, and they will come to you. HALF the PRICE of TOYOTA. They have a page on u-tube.

 

@Ethan Guzman @prov304 :

how many miles on it?

 

It's got 176k so lots of miles and upon completing all of the above, all of the above had never been done. But positive news was that the rattle was less this morning and then I started it up again later in the day and no rattle at all. I'll probably drive it a short distance tonight and then try again tomorrow morning and if it rattles, take it to a shop nearby to test for exhaust leak and headgasket issues and if there is an issue, I'll look up gasket master. It does look like cleaning the injectors has helped but time will tell. I'm starting to think that maybe Prius may be sensitive to cheap gas - I may have used the cheap Walmart gas one too many times. Any opinion on cheap gas possibly causing issues like this? I saw a couple of videos suggesting that Exxon and Shell were a couple of the better stations. Thanks for the responses.

 

The feller haven’t done the head gasket leak test yet. Can’t throw money at what’s not confirmed bad to be replaced

 

Well I took it to the Toyota dealer to see if they could test for a HG leak and they said it didn't rattle or show any signs when they diagnosed it there and that they saw no signs of a HG leak during a pressure check. I took it home and replaced the fuel injectors and it rattled less so I thought I was ok based on dealer feedback. Started it up a few days ago and it rattled far worse so I checked coolant, oil levels and all looked good with no evidence of water but then I checked the oil cap and saw the sludge of despair. I called GasketMasters and they are planning on coming out for the repair/evaluation. I'm opting on engine rebuild install vice HG replacement because I had one done years ago only to fail shortly after. At this point I'm convinced that the 3rd gen Prius is a horrible vehicle with apparent almost guaranteed HG failure in all 3rd gen models after so many miles. I'll probably sell soon after repair because I don't need this kind of trouble. Might have to go back to an old faithful regular gas engine. I saw that GasketMasters has great reviews and horrible ones on this site and bbb and google. With all the conflicting reviews, are they good or bad for installing a rebuilt engine and should I keep my appointment with them to install a rebuilt engine or try finding a local shop in Pensacola to do it - if anyone knows of one, please refer them. Gasketmasters quoted about $1k above the cost of HG repair for a rebuilt engine install at about $3600 with a 3 year warranty so that's why I chose that option.

 

Sorry, I guess I had thought you were the original poster....
Sounds like the head gasket has failed. The head might be warped also.
If you do the repairs, it will cost less. I only know about gasketmasters from what I've heard
on Prius Chat so I can't say anything good or bad about them.

Maybe a new 2015 block and head would be the "best" thing for you. It has the updated pistons and rings.
And so far, they are not having problems the earlier ones are having because of the weaker rings.

I guess it would come down to whether or not you WANT to keep the car or not.
And how much money you have, and want to spend.

I just turned 280,000 miles on my 2010 Prius. Original hybrid battery. Original head gasket.
From what I've read, the ones that do a lot of city driving, had the most problems with the head gasket problems.
The ones that do more highway miles seem to have less problems.

 

Ok. I'll probably go ahead and use Gasket Masters. If they are unavailable for a while, I may try finding a whole upgraded 4th gen engine and have it installed.

Thanks

 

Have you confirmed this isn't an exaust issue? You might have a heat shield coming lose.

 

I saw evidence of water mixed with oil inside the engine when I looked on and under the oil cap, there was sludge. Not saying there's not an exhaust issue but I think there's definitely an engine issue at this point.

 

Just an update, I tried getting in touch with Gasket Masters but it fell through so I had to look at alternatives. After watching a ChrisFix video, I decided to try Bars Pro Head Gasket Fix. Short story, it seems to have stopped the rattle, at least for a while - just had to be careful to keep heat on high and put the car in maintenance mode and ran about 15 minutes. I only used about 1/4 of the bottle. Now it only rattles a little on startup. My plan is to get the head gasket fixed eventually or to put in a remanufactured or used engine. I'm thinking that a good option if I buy such a used vehicle in the future will be to get a maintenance warranty. I checked with Car Shield and they said they'd insure a Prius with the mileage mine has for a little over $100 per month but they only will cover the engine, transmission and water pump - not the hybrid battery. Also I think they said the warranty kicks in about 3 weeks after purchase and after you've driven 100 miles - does anyone have experience with them? I'll probably get away from the Prius eventually and sell it after fixing but for now, things seem to be working. I'll plan to update once I get the repair if I can find the right shop in Pensacola to do the work at a reasonable price.

 

I had the same exact problem with my 13 Prius that had 132k miles, except I was losing coolant in very small amounts. I did not see any sludge in the oil cap or the oil. I did everything you did minus the injectors. It ended up being the head gasket between the #1 and #2 cylinders. I swapped out the head for a rebuilt one and the shop told me to check the block for flatness. I did check it between the 1 and 2 cylinders and it was flat. 10k miles later I'm having the same problem. Pulled the plugs and the #4 cylinder plug is the photo below. I'm not losing any coolant this time, however I am burning oil (about 1/4 quart in 4000 miles. I used the video in gasketmasters to do the head gasket myself and it went well for the most part (no bolts left over).
I did have issues with a ground bolt that I left loose which ended up burning up the ECU. Replacement one works great, however I'm wondering if the ECU has different algorithms or programming than the original.
At this point I'm just going to drive it until I need to replace the engine. I wish there was a simple way to check compression on these engines.
Was the $3600 you were quoted for the replacement engine with labor?

 

For anyone considering just "cleaning the intake and monitoring the the EGR flow value via Techstream", with anything over 100K, just clean the dang thing. Even better, clean it every 50K.