Hi everyone, I have a 2005 Prius with 251k miles on it. It has two problems, one is that it knocks pretty regularly under heavy load on hills, the other is that its consuming oil. I only mention the 2nd issue because I think it might be related. I run 87 octane. Spark plugs are Denso plugs about 25k miles old (replaced them first when the knock started). It is on the original timing chain, and I haven't tried to adjust the timing. While taking the car up to the mountains, the knocking stops even under the heaviest load on mountain passes, so I'm pretty certain its pre-ignition, but not sure what to check next. With the 250k miles on it, and the engine oil consumption of about 2.5 qts per 5000k miles, I don't plan to keep the car more than another year or two, but if there is some relatively simple things to do I'd like to try them to stop the knocking. Car runs fine otherwise, 45mph average, no rough idle or any other symptoms. The knocking definitely seems to be worse as the oil level drops, which makes me wonder about #3. I just wasn't sure where the best starting point was: check the timing? I'm worried if the chain has stretched and I try to adjust it, I'll make the problem worse. seafoam treatment(s)? test/replace the knocksensor (I don't have a live scanning tool, will need to get something) test/replace VVT oil filter? I saw a reference to this, but haven't found a thread on it yet other? I am pretty sure there is oil leaking past the valves or piston rings, so I may need to try and reduce the buildup if possible. Again, with so many miles on the engine, I'm not looking to tear it down as the rest of the car will be worn out enough to not care at some point soon thanks, I look forward to learning more about these.
5. Try using 89 octane and if necessary, 91 octane and see if that makes a difference regarding the engine knock.
Hi thanks for your reply. I presume that higher octane will reduce it, as that's essentially the same as going to higher elevation in the mountains which does indeed stop the knock. I don't think higher octane would fix anything other than hiding it
Since you are in the Bay Area, why not just go to Art's Automotive (Berkeley) or Luscious Garage (San Fran) and see what they suggest and how much it would cost. Consuming that much oil, have you had to replace the Catalytic Converter yet? If you are in the market for another hybrid, you should be able to get a good deal b/c gas is so cheap. If you want electric, Tesla Model 3 in March 2017.
Nope haven't had the replace the cat, throws no codes and did pass emissions about 3 months ago. We plan to replace this in about a year or so with a longer distance electric as we drive about 110-140 miles a day. @bisco replacing a bad sensor to fix the actual problem vs. just running higher octane would be better but I could certainly just buy higher octane gas.
I am trying to give you the simplest and least-expensive solution to the problem that you noticed. The car has logged 251K miles and you are reasonably not interested in rebuilding the engine or installing a used engine from a lower-mileage salvage vehicle. Certainly after logging so many miles, the combustion chambers and piston tops may have developed carbon deposits which reduce the volume of the chambers and increase the engine's effective compression ratio, thus causing knocking with 87-octane fuel. You noticed that the problem goes away at higher altitudes. Therefore the obvious thing to try is higher-octane gasoline when you are at lower elevations. I've noticed that some Prius owners like to look for the most expensive, most difficult solution for a given problem, under the belief that their car has a problem that no one has ever seen before. An owner has an engine that burns 1 quart per 2K miles and immediately thinks they need to replace the engine - when they could just add a $3 quart of oil every 2K miles and happily drive on into the sunset. So if you happen to fit that category, go ahead and replace the knock sensor, rebuild the cylinder head, etc. But you will find the former probably was unnecessary while the latter will cost four-digits.
The motor is probably toast. Your new so welcome to you! Many many threads about high mileage knocking which is almost always lower end bearing failure. The knock sensor is most likely fine and pilling timing. You can tell if the motor feels like a dog and constantly strains. But the issue is its knocking because of a bearing failure and retarding timing won't fix that. The definitive proof is has the car ever seen a super low engine oil event that threw a engine light dtc on the dash?Low oil destroys this motor. If it has seen this don't spend a dime chasing this issue. It's done. Btw, I would bet my bottom dollar it always knock you just can't tell til it has a load on it and really knocks bad. Put the car in inspection mode and get under the front of the car and give a listen to bottom end. You'll hear knocking. Inspection mode is motor runs continuously till you shut it off. Google PRIUS INSPECTION MODE on Youtube. We are constantly seeing engine knocks high mileage now on G2's.
Thanks, I'm not looking for the most expensive option, nor is this anything unique to Prius' cars with 250k. As I said at the start, I'm not going to rebuild the top end or sink a lot of money into the car. The only reason I want to make sure there wasn't something else to do about it was my parents want the car when we buy a new one, and so I wanted to isolate the problem so I could give them the car and say "you'll need a used engine in the relatively near future." The car has never had the oil light come on or run that low while I've owned it (since 135k). I will do as you suggested Ed and see if I can hear it under idle. I'm not sure how I'd tell if this Prius feels like a dog because well, its a Prius and I never could really make that poor hamster work any harder. I've already switched to 10-40 oil on the last change to try and reduce the consumption.
OP says there is no knocking "even under the heaviest load on mountain passes". So if we can accept this observation at face value, a failed bearing is not the problem. If higher octane fuel is used and the engine oil level is regularly checked and replenished, it is reasonable that Prius can see 300K miles without further drama. I would caution against the use of 10W-40 oil in the winter season as that thicker oil may cause difficult engine starting. It would not hurt for the OP to try that but as stated above, in this case I doubt that a bearing failure is the culprit.
Thanks guys, I'll record the under-car-sounds when I have it tonight. I had the same question as Patrick since the pining goes away at altitude, but as Ed said it might just be harder to detect. We'll see. On the oil, I assumed that most of it would be being burned at operating temperature, hence the 40 wt. I'll see if I can find some 5-40 that's not synthetic or something of that sort. Not that we have winter here anyway More soon, and thanks! MJ
Trying a tank of higher octane is a simple and cheap way to help diagnose. First thing I'm thinking is it's carbon deposits near the top, both increasing compression ratio slightly and getting hot enough to cause pre-ignition. Maybe some cleaner??
I had a Toyota Tercel with 200k+ miles knocking heavily and burning up to a quart of oil every 300 mile tank of gas on very hot days. I ran midgrade 89 gas and topped up every everyday with the cheapest heaviest 20w50 weight oil I could find. Then I gave it to my uncle. The car was smoky but never broke down on me and I felt no guilt passing it to my uncle. I told him he could put a new engine into a car worth no more than $500 or he could continue what I did. I'll give the same advice to OP.
Here's a recording, from both in the engine compartment and underneath the oilpan. Try not to get dizzy
