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Lexus LS 400/LS 430



  • wwestwwest Posts: 10,706
    The expansion tank cap is rated at 17lbs.

    I sealed the crack with epoxy and if it holds we will see...

    The engine coolant temperature gage is rock solid at 2.3 marks and has been since the beginning.

    Maybe a pint within a week but the car isn't driven often enough to really say.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,404
    Also (gulp) check your automatic transmission for coolant intrusion.


  • wwestwwest Posts: 10,706
    Hadn't thought of that...

    Via the ATF cooler inside the radiator...??
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,404
    Yeah, a long shot and a dreadful situation but hey, it only takes a minute to check. If you see "pink and frothy" like a strawberry milkshake, you're in deep doo-doo.


  • wwestwwest Posts: 10,706
    Just pink...thankfully.
  • wwestwwest Posts: 10,706
    The coolant reservoir holds at 20PSI for longer than I was willing to wait.

    ATF looks clear pink.

    Engine oil looks normal.

    Car parked in leaks on floor.

    Lost ~8 ounces, 10 miles to, hour dinner, 10 miles from. Tank was at 10PSI of its own accord when we arrived at the restaurant.

    No obvious "smoke"/steam/vapor at startup or with low gear coast down, DRAMATIC coastdown, high intake vacuum.

    One other anomally..

    At ~40MPH and 1500RPM the car "tugs"(***) once in awhile. Turn off the OD and drive 40MPH, or drive at 1500RPM no "tugs". 45MPH in OD no noticeable "tugs".

    OD lockup clutch slipping...due to line pressure being too low..??

    *** Feels as if something pulling backwards just momentarily. First thought it was an engine miss.

    Engine RPM remains constant but that may be meaningless since the ECU drives it not engine directly.

    Ran the car in diagnostic test mode several times with no resulting codes.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,404
    Well, leaking or other possibility under the laws of physics as we currently understand them. :P

    You aren't drinking this stuff are you?

    I think you need to pressurize the system with a pump, about 3-5 lbs above cap pressure (no more) . Get under, look for leaks...if none....then pull spark plugs one by one (while still under pressure) and look for coolant on the tips.


    (Don't forget to set your clock ahead one year before you go to sleep!).


  • wwestwwest Posts: 10,706
    I removed the fill cap and installed a rubber plug with a valve stem epoxied in place. System held 20PSI for more than an hour. I'm becoming very much afraid that I have a head gasket leak....

    But strange that no vapor out the tail pipe.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,404
    The head gasket doesn't have to leak into the combustion chamber per se. It can leak to the outside, or to the oil galleys. Besides, in cold weather this vapor would be hard to spot above and beyond normal water vapor you see at this time of year.

    The pressurization test should reveal all, especially if you can get up on a lift. If you see no drips under pressure, then it's time to start pulling spark plugs.

    Leaks can be tricky--they can travel along the length of the engine, they can get burned up by exhaust, etc.


  • wwestwwest Posts: 10,706
    The problem that the 20PSI does not show signs of leaking down in under an hour.

    Leaving me with the thought that I have a slight head gasket leak. Head gasket leaks can allow combustion pressure into the coolant system or coolant into the cylinders when there is a high vacuum there.

    I see no signs of combustion pressure and the HARD coastdown in low gear doesn.t produce ANY "white" smoke.
  • I have an LS 430 UL package with Nav and XM with the antenna mounted on the passenger side trunk lid. So my problem.. the XM sound is working fine, the presets work and the tuning works... but I have no text (artist and title) and the word "antenna" flashes in the upper display. If I use the manual tuning dial I see the artist and title info for about one second then it goes blank and the word antenna flashes. Any suggestions?
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,404
    Well, nowhere to go from here without further testing. I guess you could dump a sealer into the coolant but that wouldn't really provide the answer, even if the coolant loss stopped.

    You can also test coolant for combustion gases with a test kit.


  • The antenna is on the driver side.
  • wwestwwest Posts: 10,706
    So, off this AM to buy some coolant system sealer/sealant.
  • wwestwwest Posts: 10,706
    Changed spark plugs this AM, several were so hard to get out I had to back them back in a bit and then continue removing. 150,000 plus miles might do that. New plugs went in easily.

    Had 20PSI in the coolant system the whole time but no signs of moisture on any of the old plugs. Seven of the old plugs look just as expected(***), with the 8th one being very slightly more tan vs the grey of the others. Coloration on the "grey"plugs extends down to level with the plug skirt/threads while the "tan" one extends only halfway to that point.

    In normal times I wouldn't even consider that slight difference as a symptom.


    "Normal", and "Normal Life" pictures. Old plugs looked more like "Normal" rather than "Normal Life".
  • wwestwwest Posts: 10,706
    " other anomally...."

    A fix, maybe...

    1992 LS400 factory shop manual volume 1, page AT-43:

    "(4) Shift-up to O/D will not occur when the engine coolant temp. is below 60C (140F) and the vehicle speed is below 60km/h (37 mph)."



    LS400 "coolant temperature sensor"

    Found a number of instances of sensor failure.

    When I removed the sensor it came apart in my hands...

    New one was ~$30.

    No reoccurance of "miss" in O/D at 40MPH.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,404
    Ah, well, your tip off would have been the tach needle jumping up during the "miss", since you were actually downshifting?


  • wwestwwest Posts: 10,706
    Well, no. I watched the tach and the speedo pretty carefully/closely and neither seemed to move. And remember both of these instruments are not directly driven but driven from the engine/transaxle ECU module by D/A converters.

    And I suspect what was happening was that the sensor would go open circuit intermittently and maybe for just short, sub-second, durations. The only time this would have any affect was when right in the "cusp" of the ECU using O/D, or not, around 37MPH.

    Might have even been a "vibratory" sensitivity due to engine vibration at 1500RPM.
  • nvbankernvbanker Posts: 7,285
    Based upon my experience with my ES300 that did this (breached the head gasket), I didn't realize I had the failure until the engine hydro-locked on me and wouldn't turn over. What I'm saying is, you won't always smell it or see the white smoke before it becomes catastrophic. What you SHOULD experience if it is leaking coolant into a cylinder, is a rough run condition for a minute or so after start up. Something I had for quite a while before I tumbled to why it was happening.

    Some good news? After having the engine rebuilt, everything is good as new.
  • bladefootbladefoot Posts: 2
    Im trying to rescue a 92 400 with 245,000 on the clock,My problem is trying to find the AC pressure regulator /POA valve. Just trying to find one on the net with out spending a fortune!Right now she really is rough from hot desert sun baking the black paint and that little part is keeping me from enjoying my new ride-My father has a 91 that is in beautiful condition and its my goal to bring mine up to his level.
    If anybody can give me a hand i would appreciate it greatly!!!
    I hope to have some picts up very soon !And if anybody is in Tucson AZ and want to get rid of their GS 430 wheels ill gladly liberate them for what ever fee we can agree on.Thanks Bladefoot
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