My 2004 SR5 has never had a valve job, timing chain or rings replaced AS FAR AS I KNOW. I bought her at 140K, 320K now.

Have been chasing and "solving" lean bank 1 then lean bank 2 then lean bank1 for a couple of months now. By solving I mean replacing the cats, servicing the injectors, then most recently replacing the bank 1 downstream O2 sensor. New shop (to me) did a leak down test and reported that #3 probably needed rings. They recommended replacing the engine in light of the high mileage and that I want to keep the vehicle as long as I can. (The rest of the vehicle is very clean and functional. Knock. On. Wood.)

I don't mind replacing the engine as I suspect that the timing chain, valves, etc MUST NEED some attention just from the number of miles on her. And it's been 1200 miles since the last "fix", the O2 sensor, was made. No CEL since then. The fuel trims are little higher on bank 1. And she is running great at the moment.

Question: Drive until it gets bad enough to replace engine or be proactive and bite the bullet now?

Discuss....

I'd drive it until things get worse but may start looking for a lowish mileage used engine so you're prepared. I do wonder if it's mainly the timing chain/tensioners that are giving you these issues. I think there's a simple way to check chain stretch. Maybe throw a bore-scope down the plug hole to check the cylinder walls especially on #3.

Thanks for the reply, Mike.
What would one be looking for on the cylinder walls? Confirmation of the poor leak test, i.e., rings are bad? Would I be scratching my head harder if the walls look good? Ha ha!

Just drive it. I would however get a second opinion, especially if you are looking at getting a new motor. I’m surprised at failing rings. I see these motors with 400/500 thousand miles on them. If you are going to spend that kind of money definitely get a second opinion!

i would say, it's your timing chain. how much oil consumption do you get?

Sorry, got distracted by my daughter's Hyundai.

Asylvester: 400-500K, huh? That sounds awesome. Second opinion sounds logical.

4R-4ever: Little to no oil consumption. bSuppose I could remove the tensioner cover and see how far out it is?

Thanks for the replies.

Downstream is after the cat, is that what you mean? Because that only reads emissions, doesn't affect the mix. Both banks though so your issue is most likely a vacuum leak regardless. Leakdown tests are pretty easy, consider getting a gauge and doing one yourself, or definitely get a second opinion without telling them anything prior. Not to say it can't happen and I haven't done much with the 1GR, but never seen more leakage from rings than valves if both are untouched

Yes, the O2 sensor not the upstream A/F sensor. Good advice, jvtbt. Think I'll get the leak down gauge.

If there is little to no oil consumption that is great news, your rings and valve stem seals must surely still be in good condition. I am not an expert but just going on what I have read from general interest on here, another vote to get the timing chain condition verified.

Yup. These are pictures posted on this very forum! There are more but I did not want to take up too much space.

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When we bought our 2009 4Runner it had 156K miles on it. My wife’s friend thought we were crazy buying a car with that many miles on it. They don’t know Toyotas. They drive other brands (I’m being nice here by not identifying the brand). But their idea of life expectancy out of a car is much less, and for good reason because their cars don’t go that long. So it’s worth fixing, even at that mileage. Please keep the post updated with your findings as I’m very curious to know. Thanks and good luck!

Almost 300K on my 2008 v6 SR5 and I plan on driving it until 400K+....or as long as it goes.... 😁 Change the oil and do the maint. and it will take care of you.

You would see gouges on the cylinder walls if there is a broken ring. As mentioned that usually comes with oil consumption and or extra blow-by into the crankcase. Second opinion is definitely a good idea on the compression test.

I rebuilt my 2004 V6 engine which came out of a wreck i bought to replace the locked up engine in my sons 04. When i actually got inside the engine the 280K mile rod and main bearings actually looked better than the new ones i put in it and believe it or not i pulled out the micrometer and the original bearings were a tiny bit thicker than the replacement bearings.

OP, you ever send your oil for analysis? That might help rule out issues. I was just talking to "my parts guy" at the dealership I usually go to. I asked about rebuilt transmissions, just to get an idea so if I ever need to do that. I decided to ask if Toyota does remanufactured engines. Again, just for background info. He seemed to think it was better to go to an engine shop, from what I gathered. I guess because theyight have more info on sourcing engines. Apparently near me, there's someone who can import low mileage engines from Japan. And then further, I suppose that's because Toyota is still using the 1Gr-Fe, in my case.