1992 Lexus LS400 Blue Smoke on Startup

LEXUS
Avatar
ELLISMACK
  • MEMBER
  • 1 POST
lexus 92 ls400 v8 230k miles
smokes on start up and then clears, heavy smoke after setting up for a couple of hours, had it checked
codes stated mass air flow meter, and knock sensor
had air flow meter replaced , did not help. did not replace knock (expensive). noticed some black
reside in tail pipe. Any suggestions?
Feb 17, 2007 at 3:02 AM
Advertisement
Avatar
SERVICE WRITER
  • ✓Experienced Mechanic
  • 9,123 POSTS
sounds like its burning oil. Might want to bump up the oil viscosity a grade.
Feb 17, 2007 at 8:12 AM
Avatar
KIN CHAN
  • MEMBER
  • 453 POSTS
blue smoke is oil
black smoke is running rich --> too much gas
white smoke is water or coolant in ur combustion chamber
i don't think the blue smoke have anythign to do with those 2 sensors ...when is cold ur cylinder head valve seals are hard ..cuz they make out of rubber..and ur car is high mielage..once it warms up it get soft so it seal up the oil dripping from the cylinder head to the combustion chambers ..make sense ? ...good luck man..
also..whenever ur car misfire ..ur engine runs unevenly make some engine noise ...knock sensor detected it ..generate a code thats all it is to it ...it just doing its job...ur code is knock sensor ..not knock sensor bad..it also can imply the computer is getting some abnormal signal that its outta a good operating range --> misfire!!
hey these guys here on this website are really good guys ...they let me come aboard to be part of their team...try to give em' some support if u think my answer worth anything ...thanx man...
Feb 20, 2007 at 12:58 AM

Suggested Repair

Blue smoke after sitting points to oil burning, likely hardened valve stem seals on this high-mileage engine. Consider a slightly higher oil viscosity and inspect the valve seals; the replaced mass airflow sensor did not fix the smoke, and the knock code may only reflect uneven running or a misfire.

Conversation Summary

A 1992 Lexus LS400 with 230,000 miles smokes light blue on startup, clears once warm, and smokes heavily after sitting a few hours. Mass airflow and knock codes were present; replacing the airflow meter did not help, and black residue was noted in the tailpipe. Replies say blue smoke is oil, not those sensors, and that cold, hardened valve seals can let oil into the cylinders until they warm and seal. A higher oil grade was also suggested.

Related Repair Questions

Add a reply
Join 2CarPros for free, one of the most advanced car repair communities on the internet. From first-time drivers to seasoned mechanics, everyone is welcome to reply, share details, and get better answers. You can add a temporary image or video first; uploads are limited to 20 MB.

Ask a new question

Frequently Asked Problems for This Vehicle