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Just picked up a beautiful 1998 Lexus LS 400.
I am also new to this forum, eager to join y’all.
The previous owner has been using regular fuel, manufacturer says premium fuel only. Now it runs fine on regular but I believe that premium may help clean out the engine a bit. It has ~360k miles, (beast) so what do you guys think.
Another thing. Can’t seem to find the heated seats function if I have it, not sure if it does.
Premium fuel does not "clean out" the engine. Different fuel grades sold by the same gas station are identical. The only difference is the octane rating. Premium gas doesn't have more "cleaners". There are special exemptions where you have fuel sold in California, in general, sucks for a variety of reasons.
The big difference which actually matters is brand-to-brand. Certain brands (like Shell) use a different additive pack for their fuel compared with other brands compared to Jim Bob's haircair fuel and tire center. Most gas stations out there use "Top Tier" gasoline, which is a certain formulation with a standard of certain additives.
This being said - the octane rating does make a difference. The engine is specifically tuned for premium fuel, and not running premium most likely will result in your engine running more conservative timing and losing out on some of it's ability to make power. This is not just applying to full throttle redline, this means the entire area under the curve. This doesn't affect our car nearly as much as modern turbocharged engines do, where they will run substantially less boost and cut timing loosing 15 or 25% of their rated horsepower. But it's still impactful for the 1UZ. Here's the thread talking about it.
Additionally, you're also relying heavily on the knock sensors to do their job and protect the engine since you're running low-octane fuel. Personally, if I'm going to be doing a 1000 mile road trip, I will fill up with regular gas and avoid full throttle. Otherwise, I run premium as I like to... explore the utility of my throttle pedal frequently.
The switch for the heated seats is instantly obvious, right above the gearshift lever. They're not hidden, so, it seems you don't have them.
Last edited by 400fanboy; Oct 31, 2023 at 12:09 PM.
The big difference which actually matters is brand-to-brand. Certain brands (like Shell) use a different additive pack for their fuel compared with other brands compared to Jim Bob's haircair fuel and tire center. Most gas stations out there use "Top Tier" gasoline, which is a certain formulation with a standard of certain additives.
This being said - the octane rating does make a difference. The engine is specifically tuned for premium fuel, and not running premium most likely will result in your engine running more conservative timing and losing out on some of it's ability to make power. This is not just applying to full throttle redline, this means the entire area under the curve. This doesn't affect our car nearly as much as modern turbocharged engines do, where they will run substantially less boost and cut timing loosing 15 or 25% of their rated horsepower. But it's still impactful for the 1UZ. Here's the thread talking about it.
Thank you 400fanboy. I find the thread to be very informative.
Is one brand often considered to have a better high octane formula than other gas stations? I have also heard good things of Shell, but is Costco also reliable? I imagine it doesn’t matter much but Costco gas will save me some money.
If you're driving a tuned Mclaren running on the ragged edge, sure, you want to be careful. You want the best gas, and, you're probably putting some octane booster in ontop of that.
But for our cars, it really doesn't matter. It'll be fine. Just get whats cheapest that isn't "jim bob's". And yes, Costco is fine.
like you said regular will "be fine" for just getting around but if you want to enjoy those lovely higher RPMs without fear of pinging or knocking you want to make sure premium's in there
also is there anything that would make you think the engine needs to be cleaned out (so to speak)? with 360,000 miles it sounds like it should be fairly free of build ups lol... as was stated above the only reason premium is recommended is because of the higher compression ratio in the 1UZ, with too low an octane the fuel can ignite before the spark which throws off the engine timing and can lead to real issues
i'd fill er up with premium, give it a bit of the italian tune up, and enjoy the pinnacle of the relentless pursuit of perfection era of toyota!
I bet you this car doesn't have its original catalytic converters. I ran regular for 30k miles in my old 97 LS with 250k when I bought it and it threw P0420/30 Cat codes for inefficiency about 30k miles later. So it does wear out other parts of the car. I didn't care at the time since I used it for commuting 80 miles a day and gas was 50 cents more for premium so it was a considerable savings using regular. But on my 99 LS, I only use premium and it has the original cats and everything is working great. Only has 168k vs 300k, but whether extreme cold or hot it hasn't knocked or made any irregular sounds.
also is there anything that would make you think the engine needs to be cleaned out (so to speak)?
Not anything in particular but I don't exactly know how the previous owners treated it. I gave it an oil change and filled it up with full synthetic 5w30; the oil was quite dirty (and I did the oil change early). Was thinking about giving it an engine clean but it might simply be unnecessary.
Premium vs. Regular fuel
