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Oil Pressure Light - 91 Ls400


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About 6 months ago I purchased a very nice 92 LS400 with only 72,000 miles. I've put on about 11,000 since then, "highway miles". The previous two owners were "mature" in age and took car to dealer for most of services. The second owner decided to quit paying $90/hr and took it to another place, who decided to do a lot of preventative maintainance, such as put in the green anti freeze, put in Dextron III ATF, and "clean the distributor rotors", and some other mysterious "repairs". No wonder the 2nd owner was so willing to part with this "hanger queen". Fortunately this took place within the past year, not not too many miles of "after market" maintainance.

My first tasks, after getting the vibrations out, alignment and balancing, and getting right rear wheel "straightened", was to immediately put in Amsoil in engine, tranny, and differential. Also a radiator flush. with Toyota/Lexus red stuff.

It's been running very fine, but a bit harder ride than my wife's 96 with 185,000 miles.

Problem is for the past few weeks, while cruising (about 80 mph), just going with the flow ;) , the low oil pressure light illuminates. I let off gas, and the light goes out. This has happened about 15 times so far, and the light never stays on more than 2 or 3 seconds, once about 5 seconds. The temperature gage is always stable (both cars always at just under 1/2 heat range).

Of course the manual tells me to pull off the road immediately and call the Lexus dealer. The oil level is full, and no other indications of a problem.

Has anyone else ever experienced this with their LS ? Trying to decide next step. Not willing to open up my wallet and ask the dealer to help themselves. They are definitely in it for the "business".

Thanks for suggestions. :wacko:


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Welcome to the LOC!

I've heard the Gen I LS's have the "stiffest" ride of all - compared ti your wifes (Gen II) and my 99 LS.

About the oil pressure switch.....

It is next to the oil filter so you could replace it out next oil change. I don't know if they're expensive though?

I have a theory that maybe some "sludge" is lodged up in the switch which could be causing the signal to trip. Amsoil does a great job of "cleaning" the engine. I changed my OIL filter only after 1000 miles of using Amsoil 5-30W in my 99 LS. (The first use of synthetic oil in this engine). This was recommended to me because of how much "dino oil sludge" that could be broken free and trapped in the oil filter the first few times using SYN OIL. Since the oil pressure switch is next to the filter - maybe its clogged too? <_<

Per specs:

idle pressure is 4.3 psi

3000 rpm is 43-85 psi

Anyway, six months ago you change the oil - isn't it time again anyway. I'd give you a chance to at least examine the oil pressure switch and get some fresh, clean oil in there - should help!

Good Luck,


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Normally- if it were a bad oil pump the light would illuminate when the car is idling lower, rather than higher. I think you said that it went off when you released the accelerator. That is strange. Perhaps 99LS has something there.

About the ride quality- do you know if the struts were ever replaced? My 90 LS400 has a smooth ride, but not until I replaced the rear struts with Toyota (factory OEM) struts. It is actually a little floaty at times on the freeway. The previous owner had installed KYB performance struts and the ride was very stiff. The OEM's give it a once again, smooth, factory like ride. I have seen several 90-94 Lexus LS400s, literally FLOATING down the road, but this could be from worn struts. Some models have the air suspension and I think that suspension is a little softer as well. Does your car have the air suspension?

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What a great forum. Yes, time for an oil & filter change, this weekend. I was hoping that the light was from a malfunctioning pressure switch and need your input BEFORE I changed the oil, just in case it was a bigger problem and needed the pump replaced (along with the "new oil").

So, it's checking the price for a new oil pressure switch, cleaning this one, then oil and filter.

Thanks 99lsguy, 90LS400, and skperformance for your replies. Most helpful.

BTW, the struts have not been replaced on either vehicle. We still drive the 96 LS with 180,000 and have had no problems at all, besides the dealer replacing the PS pump - supposedly due to leaking onto the alternator at 99,000 when they did the timing belt change. Fantastic car, that's why I replaced my 89 Honda at 260,000 with the 91 LS. (the poor little honda's radiator burst and it overheated etc. without any temp indication at all - at night).

Only other problem with the 96LS has been the brakes. The rear pads wore out while the front pads were only about 1/2 worn. And both cars now need new front rotors. Turned rotors the 96's at around 100,000. Just gaining experience :rolleyes:

99lsguy, I had been using Mobile One for the last 100,000 on my 96 and decided to try Amsoil, since they have the 25,000 guarantee (with a 6mos/12,500mile filter change). My experience using synthetics is mostly with the jet engines I flew and am a "believer" in its value.

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Jets & LSes - probably a personality type - I remember a long long time ago, answering the question to get into the AF, "Do you like to drive fast?"

Silly Question, now at a more "mature" point in life, I like comfort, reliability, class, and speed. Even a fast mono hull sailboat will do for cruising and racing.

Bought the 96 LS new - when I thought we had a lot of money. Put all 180,000 on it ourselves. Watch out for some of us "old geezers" :cheers:


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  • 2 weeks later...


Added 1/2 qt oil and sure enough, so far at least, the light has not yet illuminated. That's in about 300 miles of driving. Although I bought a new oil pressure switch from Napa, may have to return it. We'll see...

Sent oil sample for analysis "just to know" what it will say. Always wanted to have one of those done. Perhaps I'm getting a bit lazy in my old age, but, getting tired of doing oil changes every month or two, on two cars. Will let you know results of oil analysis on my Amsoil.

Thanks for the tips and ideas. :rolleyes:

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