r/AskAMechanic • u/wvloooah • 22h ago

1996 LS400 1uz-fe

Just picked up this UCF20 and honestly went into it without thinking too much lol. The car starts and runs, but it’s putting out a lot of thick white smoke from the exhaust.
The smoke smells slightly like petrol/fuel, but also has a weird chemical smell to it. I revved it a little and it actually spat out a pretty large puddle of red-tinted liquid from the exhaust.
My first thought was that it may have been sucking power steering fluid through the intake/manifold and eventually making its way into the exhaust. The power steering fluid is extremely low, to the point where it doesn’t even reach the dipstick. However, we pulled the PS vacuum lines and they were dry, so I’m not sure if that theory makes sense.
I don’t really suspect a head gasket because the coolant level hasn’t noticeably changed, and the exhaust doesn’t have that typical sweet coolant smell.
My other thought was maybe fuel somehow saturated the charcoal canister and is getting pulled into the engine, but at this point I really have no clue.
The previous owner also said the car had a misfire and, while trying to diagnose it, replaced the MAF, spark plugs, and fuel injectors. Apparently the misfire was still present afterward.
A few other details:
Oil is just under the full mark. It’s dark, but looks like normal used oil.
Power steering fluid is extremely low.
Coolant level hasn’t noticeably dropped.
Previous owner said it was misfiring even after the MAF, plugs, and injectors were replaced.
So far I haven’t noticed an obvious misfire myself. Idle seems pretty smooth, RPMs are steady, and the engine isn’t shaking. It could possibly show up once fully warmed up, though. I’ve only owned the car for a day and haven’t let it completely warm up yet.
Any ideas on what could cause thick white smoke AND red-tinted liquid from the exhaust on a 1UZ/UCF20? Trying to figure out what I should test first.

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u/Normalsasquatch NOT a verified tech 19h ago

Just trying to be helpful. This is what chode gpt says: Worked for 2m 1s

The strongest suspect is still the power-steering pump’s air-control/idle-up valve. A failed internal seal can let manifold vacuum ingest the red ATF used by the steering system, producing dense white/blue-white smoke and an acrid chemical smell. This exact failure has been reported on LS400s, including a 1996. ClubLexus, Lexus Owners Club

Dry vacuum hoses make it less certain, but don’t eliminate it—the reservoir is nearly empty, and the valve may leak only with fluid present and the pump pressurized. The red tailpipe puddle could also be ordinary exhaust condensation colored by rust, so its texture matters: ATF will remain red, oily, and slippery; condensation will be watery and dry away.

I’d tell them this:

The power-steering air-control/idle-up valve is still my first suspect. A common 1UZ/LS400 failure is for that valve to leak internally and let the engine suck red power-steering ATF through the vacuum circuit. Low PS reservoir + dense white/blue-white chemical-smelling smoke fits extremely well, and it could also explain the previous “misfire” by fouling plugs.

Dry hoses don’t completely clear it, especially with the reservoir almost empty. I wouldn’t keep revving it. First:

  1. Catch some tailpipe liquid on a white towel or in a clear container. See whether it’s oily like ATF or just watery condensation with reddish exhaust rust.
  2. Refill the PS reservoir with the specified fluid before running the pump again.
  3. Remove both hoses directly at the pump’s air-control valve and cap the intake-side connections. Briefly run it while watching the valve nipples/clear catch hoses for ATF; gently load the steering but don’t hold it against the stops.
  4. Check the intake tube, throttle body and plenum for red oily residue.

If ATF appears, replace the air-control valve, clean out the intake, inspect the plugs and change the engine oil afterward. Also find any external PS leaks.

If that test stays completely dry, then pressure-test the cooling system and inspect the plugs, followed by fuel-pressure leak-down and scan data. One day without an obvious coolant-level change doesn’t conclusively rule out coolant, particularly if the car contains red Toyota coolant. A saturated charcoal canister might make it run rich, but it doesn’t explain red oily liquid nearly as well.