Hmm I wonder if more frequent oil changes may help. 3k miles or 6 months whatever comes first. Plus 5w-30 maybe try? Also try Toyota oem air filter in case you got after market and maybe premium gas 91 or higher octane for several fill ups or so. More explanation below.
I have a 1999 100 series with 296,000 miles and I sent mine in at 287, 000 miles after getting from previous owner and seeing dark oil and not a lot in car and that was on cold. I got very good results from blackstone and even though blackstone said to change at 7500 miles new one and said again even after my second sample I sent them, I am doing consistently 6 months or 3k miles and I am using only 5w-30 even with temps here in Toronto Canada going to 105-108F in summer or like -20F or below in winter (I just let warm up 1 min or so always) and I use only conventional and only from Toyota. I know shocker for many at times. About $5 Canadian a liter so it’s cheap at dealer (made by Mobil 1 still) and with Toyota filter ($5) about $40 total per oil change and I do myself. I’ve opened it up and it’s clean inside and I don’t need synthetic thin oil and it’s been working great in high temps. I will probably always use conventional on this. Plus if I want cleaning power of synthetic I do that with premium 91-93 octane fuel. Top tier fuel does help engine condition and works hand in hand with engine oil. Proven by the oil guy on YouTube (son of the nascar race driver and who helps their own race car team).
Even with its thickness of 5w-30 plus conventional my 3 now engine oil test results over last two years have been very good and gotten better over each. Prob won’t send in any more for several years bc I stick to 6 months or 3k miles religiously. 3k miles or 6 months is what Toyota and Lexus experts are saying and now so many YouTube mechanic experts with their channels who service all cars are saying same interval or 6 months 5k miles on synthetic). Because for most of us we do severe driving conditions and fall under that interval.
If your’s is having high levels, see if they still improve for you with more frequent oil changes?
I get this engine is easy on oil and so over built but you’ve got issues here you aren’t sure about, to me I’d go straight to more frequent and with 5w-30 and with conventional. Or at least 5w-30 synthetic with more frequent combo?
OH also, I know it’s bit more expensive, try Toyota engine air filter first. Not after market or K & N. It def makes a difference. Try that. If u end up improving things via these various ways, you can go back to aftermarket. But I learned from couple experts and I was like really? Fine I’ll try exact Toyota one and yea I can see in my sensor readings with fuel to air ratio etc Toyota air filter made difference. In case you didn’t use Toyota one. Just had that idea pop in head.
Oh and try premium gas maybe? I know costly but try from like shell or tier 1 gas pumps. Mine recommends 91 or higher, lx model, and can run just fine on 87 regular but when I discovered it was so clean inside, man I just wanted to keep it going clean. And horsepower went up and so did fuel economy by about 1.5-2 mpg on highway. Compared to 87. In ur case premium may help clean out other parts inside. At least for few months of trying and seeing?
If u have obd reader check ur fuel to air ratio on your two short banks and long term banks. I wonder if car adding more fuel or too much air getting in from somewhere.
Also open up your engine oil cap, any weird stuff in there? Like on bottom of cap? Or in the hole? Milk shake looking? Also check in your radiator if u open up ur cap (only when car and radiator are cold). Milk shake weird stuff on bottom of cap or in radiator when you look at fluid? In case coolant and engine oil mixing somewhere
I know im throwing lots at you but this is how I baselined along with premium gas changes (again my 99 LX calls for premium per book and stamped across car) and ended up tuning it very well and it shows in results and in higher mpg than I was getting before. I also did spark plugs and coils and handled a slight valve cover gasket leak that was leaking into spark plug tube gasket area.
Fyi I also baselined transfer case with liquid gold from Toyota ($50/ can Canadian for Super Gear Oil which is what it came from factory and conventional) and I thought it drove well before, it became even better, and in transmission put back in Toyota Dexron 3 conventional (4 drain and fills before discovered fluid exchange on ours via trans cooler lines) and front diff and rear diff I put in also conventional exact weight as said in service repair manual. And I sent in those old oils, the valvoline max life one fit all one previous owner was using for testing and results were good but I still wanted to change bc I know last guy towed and slightly elevated iron levels showed up in testing on 25k mile old oils. Call me picky but I got that thin stuff out and put in conventional because again I can easily change at home and do like 15k miles instead of 30-60k miles and also avoid leaks and I’ve changed breather valves and this was made for conventional. Sure can use synthetic like my newer Lexus’ which I stick to on those but again I know this 99 is clean in all places per my drain plug magnets and using borescope or opening up. Yours may need synthetic to help current situation. not sure. So stick to what you want but maybe do changes more frequently and see maybe it may help? Maybe switch to 5W-30?I get people want cleaning power of synthetic and thinness for temperatures but conventional works fine for me in freezing Canadian winters and 100-110F in my area in summer. I have obd reader hooked up to my car play I put on and I monitor all sensor readings and temps and things in perfect range in winters and summers, knock on wood it stays.
Sorry for long essay it’s 2 am here and too tired to go back up and revise and shorten lol. But I hope it helps! It’s combo of lots of knowledge I got from some great 100 series experts and mechanics. And it’s been such a joy to work on myself for past two years of ownership.
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