This is on a 2012 Plug-In, with about 248,000 miles. I was getting pretty bad rattle on startup, much of the time. Removed and cleaned out EGR cooler really well, new EGR valve, new intake manifold. Started up in Maintenance Mode, and it ran really smoothly, so I thought that seemed good, but then it just started rattling in the middle of a smooth idle. Rattled for a couple of minutes, then smoothed out again, then rattled again. Some steam out the tailpipe, and a drip. Compression was 185, 184, 180, 180, but have been getting moderate coolant loss. Applied compressed air to cylinders using the hose from my compression tester with the schraeder core removed, and moderate leak from Cyl1 to coolant, smaller leak from Cyl2 to coolant, and nothing from 3 or 4. Didn't seem to be leaking past the rings or valves, or into the oil, so decided to do a head gasket, or at least pull the head and check it out. Almost done getting the head off, but thought I could use some advice on this SLUDGE! Everything in the cam train has a coating of sludge. And when I drained the oil, cold, it shot out normally when I pulled the plug, but at the end, it was slow, thick glop oozing out. Oil not milky, though, and oil level was never rising while coolant level was going down. I'll go finish getting the head off while waiting for sage advice! (Or brutal chastisement!)
The "sludge", is coolant in the oil. Normally, on the Prius you don't get that unless it's really bad. Since you kept driving it, it just got worst. You likely have a warped head. Make sure the check it. Or take it to a machine shop so they can check it. If the head is not warped, or if it is, it's not bad enough that they can't machine it, and you re-install it, you'll need to change the oil after getting it to operating temp. And the filter also. That should get most of it out. Then check the oil after few miles and see if it's clear. If it's not, change it and the filter again.
Is this the same car that you added a stop leak product into the engine cooling system in a post in December 2024? https://priuschat.com/index.php?posts/3501992 If so, it is time for a replacement car.
I appreciate all the feedback. It cleaned up pretty well, and I did the head gasket, gambling on the bearings and rings since compression was all above 180. @ASRDogman, I'm still wondering whether it was coolant in the oil making the sludge. The oil was all dark brown and clear, not milky, and the level was never rising. @Brian1954, yes, this is the same car. That waterglass treatment lasted about a year. I don't know if it caused this sludge or did other damage, but coolant passages in the block and head had no trace of it, and the radiator and heater core have been free-flowing the whole time. I don't remember why I chose a Mahle head gasket kit instead of Toyota or Fel-Pro. It certainly wasn't cheap. But the injector o-rings didn't fit right and I didn't notice until I fired it up and gasoline was spraying everywhere, so I put the old ones back in. It sounded great when I got it running, but then it had a couple of slowdowns and recoveries and shut off with a rattle and the four coil codes: P0351, P0352, P0353, P0354. I have checked all grounds, and checked from pin 4 in each coil connector to ground on the valve cover, chassis, ECM case and inverter case. All zero or 0.1. Checked all four IGF coil connector pins (pin 2) to ECM pin 23 for resistance or short to ground, and checked for good +B on all coils. Someone said one bad coil can bring down all four IGF, so I got a new coil, swapped it in at cylinder 1, and had a nice long test drive with full power, all modes, no stumbles, normal temp, batteries all charged up. Next day the stumble and die, Check Hybrid System, and four coil codes came back. I tried dispensing gas from a plumbing torch all around the intake and TB, but saw no difference. Now I'm waiting for more new coils and am wondering what else I should check. Hoping it's not something I did wrong with the head gasket and it's just marginal coils. Further note: I don't know whether it's relevant, but since the new head gasket, through all the stalls and slowdowns and DTCs, the misfire counts have all been zero.
The photo you posted show oil/coolant mix. It certainly isn't dark brown. Coolant and/or gas are the only two things that could possibly get into the oil. Unless you added something. If the injector seal were not the correct size, and leaked, what other gaskets are leaking? Reusing the old seals could be your issue. 12 years, 248,000 miles, long time for gaskets that get hot. If it was running well before the issues, it's not likely a part would just fail, then come back to life. It's likely a loose connection, or gasket not sealing correctly that changes with temperature. It's seems that everyone that has gotten aftermarket engine gasket kits have issues with some part of the kit not fitting, or missing. I would carefully, and slowly, go over EVERYTHING, connectors, hoses, make sure they are solidly connected. Did you replace the spark plugs with REAL plugs? Not the cheap chinese copies....
I can't believe you did not replace the engine especially in this case. A Jdm for $1,200 is easier than the head gasket job with a rebuilt head.
I put NGK iridium 93501 plugs in a year and a half ago. Not sure if those are good, but they were what was available locally when I needed them. I'm not sure how else to tell you, the bulk of the oil came out fast and dark brown, not at all milky. At the very end the sludge started to ooze out, and there was the brown film on everything, which sprayed off easily. If I had much coolant going in the oil the waterglass would have been fatal, as far as I know. I don't know what caused it, whether it was oxidized oil plus blow-by, or maybe a small amount of coolant. Putting the old seals back in isn't a problem if they're not leaking. I'm talking about the o-ring between the top of the injector and the fuel rail. If it's not spraying gasoline, there's no problem. I'm going to get some OEM o-rings to put in there, but the old ones didn't seem bad. But none of that is my current problem. It has been out there purring away for an hour this morning in Maintenance Mode, 990 RPM, 200F, no codes, no slow downs or restarts, no misfires, recording all data in Techstream. That happened yesterday also, but then it started stumbling and shut itself down, and threw all four codes at once: P0351, 2, 3, and 4. With zero misfires. The only other codes I've seen are P0032 and P0038. If it stops raining I might do a compression test and borescope, or just wait and try the new coils when they get here. The old ones are Duralast, that's what it came with. I'm putting in Denso.
