2015 1.8L rattling at low rpm, head gasket?

The car has 270k miles, it's rattling quite a bit at cold starts. I know 3rd gen Prii have issues with head gaskets, but I'll clean the EGR if I can get the dang thing off. Those bolts aren't fun. Also, didn't the gasket issues get solved in the later Gen 3s?

Also going to swap coils and plugs as those were super cheap online. I have a head gasket test kit but I can't seem to find a radiator cap on the car. Maybe I could install it on the coolant reservoir? It's hard to keep the engine running and hold the tester in place. Rock on the gas might work...

Thanks for any advice

 

Thanks for the responses. I'll run the car in maintenance mode and do the head gasket test on the coolant reservoir. I understand that rather than coolant contamination, the symptom of cooked heads is coolant loss into the combustion chamber.

I saw a guy on YouTube who pulled his coils and spark plugs then held sheets of paper over the engine while a helper cranked the engine. There were coolant stains on the paper over cylinder 2, which he said is a common place the gaskets leak. I'll give that a try and maybe scope the cylinders if they look nasty.

Not sure where people got the idea I'm running the Indy 500 with the car or not diagnosing it. If I'm taking off the wipers and cowl to pull the coils and plugs, I may as well replace those parts as they have at least 150k of wear on them. For $60 a new set of plugs and coils is a no-brainer even just for the labor to pull them.
I've used cheap coils before, they're fine for 20k miles or more.

I also ordered the head gasket and bolt set. I prefer to have parts around before I really dive in. Based on my cursory inspection of EGR I can see that it's kinda tight in there.

The computer has permanent OBD codes for misfires on cylinders 2,3,and 4 so I think the coils and plugs are worth it even just to diagnose further.

 

I see there is a young man on Youtube who pulls his Prius engine in an hour. JDM engines are $1500 or less for this car. I wonder why people are rebuilding so much with a decent supply of these engines around?

 

Video of a cold start:

I ran the head gasket tester on the coolant reservoir. No temp gauge on dash so I may need to pull it up on a scan tool. Pretty sure I hit operating temp after 10 minutes at 2500rpm. Indicator fluid turned greenish (from blue), but not yellow. I'd say if there are hydrocarbon gases in the coolant, it's not much. Still not great obviously.



When I pull the plugs I'll do the paper over the plug wells test. I did find a scope laying around so maybe I'll post some vids of the cylinders and pistons if people are interested.

If I get coolant out of the plug wells, the cylinders are cleaner than expected, and new plugs and coils don't do anything for the problem, I'll rule it a blown head and will be sourcing a JDM engine for the car. No point in doing this head gasket repair on a 270k mile engine.

If the cylinders have normal wear and no coolant blowing out of the plug well, I'll finish cleaning up the EGR and intake, and will run it with new plugs and coils for a bit.

 

Generally when people post to automotive forums they are looking for help. I'm all for jokes about blown engines, but I actually want to get useful information from community members who know this engine. I also like to try to contribute to the community by reporting my findings, in the hopes that others who find themselves in my situation will have an account of what was done and what the resolution was.

Is anyone interested in my findings? I have the results from a compression test and some videos of my cylinders. Thanks.

 

Had the car 2 weeks. Its been driven 3 miles. Cylinders do look somewhat different, 1 and 4 are clean, 2 has some debris in it, and 3 looks charred. Compression is 120psi across the board. Spec is either 118psi or 190psi depending on where you look. All data says 118, manual says 190.

 

Welcome to the thread. What year Prius do you have, and do you have the 1.8L 2ZR-FXE+3JM engine? My understanding is that the head gasket design WAS changed in 2014, causing less cooked heads in 14/15 models.

The rattle is quite scary, but I believe people panic when it happens because it looks like what would be a SERIOUS engine problem on any other car. The clutch between the electric motor and the gas engine amplifies what might just be a bit of misfiring on the gas side. Of course it could also be the head, but assuming it's the head is a mistake in my opinion.

If you do end up doing the head gasket, make sure you resurface your head, replace the bolts, and replace EGR/PCV and clean your intake. Many people on the forums do their heads and don't get it quite right.

I've got 120psi on all 4 cylinders so I don't think my head is blown. Yet.

 

Also one last thing: this engine uses the Atkinson cycle (rather than the normal Otto Cycle in ICEs). Atkinson cycle - Wikipedia

Basically the intake valves stay open a little later, resulting in less power but better fuel efficiency. Also there is a bit of blowback into the intake manifold. This could contribute to buildup in the intake, but could also create some turbulence in the intake. Just something to consider when diagnosing.

 

Well the head gasket doesn't rattle, the rattle is caused by the ICE running sub-optimally, which creates vibration in the Torque Limiting Clutch (aka damper). The electric motor that shares power with the ICE is used to start the ICE, so there is some normal vibration at start as the system adjusts the electric motor rotation to the speed of the ICE. Clearly if the ICE is stumbling and/or misfiring, this vibration will increase. However, this would explain the vibration occurring only at cold starts going away after running for a few seconds and/or spinning at higher rpms. Therefore I conclude that bad coils/plugs/EGR/PCV absolutely could cause this vibration only at start (or during normal driving as well). Finally, the torque limiting clutch could very well be worn. It seems that the springs on this part tend to fail occasionally.

Based on my assessment, I suspect you're telling people they have a blown head when there can be many other root causes of the vibration. Repeating the jokes about blown engines likely just means more people doing unneeded head jobs or even junking their cars.

I put in my $40 coils and my $20 plugs and the car is running fine after a full cleaning of the intake system. I'll measure the resistance of my old coils just because I'm curious if they're burnt out. The plugs were beyond toasted. I haven't had any vibration at start or any other time driving. In fact, I got the car up over 100mph and it ran smoothly.