icypool

I have a 1998 Lexus LS 400 and when the car starts it has a bit of black smoke come from the exhaust. What does this mean? It happens randomly, there is no real pattern to it that I can notice. I live in arizona so cars are always out in 100F ++ weather.

(extra information) It has 90k miles and has had every service.

Thanks!

MGB

dose the care leave this smoke during heavy acceleration and can I to assume the service engine light is not on?

LScowboyLS

black smoke indicates a rich condition - have you done the basics: sparks plugs, PCV valve, engine coolant temp sensor, throttle body cleaning, air filter, checked for vacuum leaks, etc. ?

scanned for OBD-II codes?

icypool

It does not happen during heavy acceleration. The check engine light is also not on.


I'm not sure which of those things have been done. I just bought the car and had a major service done from lexus. The 90k service with a new timing belt and water pump. There is a ODB-II error code they said but they think this is related to another issue I'm having with not being able to program my second key. That's why I had to order a door control ECU and they will be installing that soon.

In case your wondering I had to find the part on ebay as they don't make them anymore.

My service advisor says that it could be a issue to do with bad valve seals but this would cost way too much money to fix and it's not worth it he says? does this sound right? He did not have the mechanics look at it though he just told me this upon telling him.

Gene01

In by experience, bad valve seals would give white smoke, not black.
LScowboy, would you confirm this?

I think your '98 is too late to have the 1st gen problem with the vacuum valve on the power steering pump.

xhifer

I doubt its valve seals but theres always a possibility. It seems you just bought the car and youve already posted a few threads of your concerns. Might be better to sell it and be honest about the problems. To my knowledge, 2nd gens rarely have the problems youve encountered. Though all of it could be as simple as a PCV valve .

PureDrifter

iTrader: (10)

the '98-00 idle up valve on the PS can still fail, though it does so at an observably lower rate.

Usually PS smoke is white though.

OP when was the last time you changed the PCV valve(s)? If it's gunked up too bad it could let some oil into the intake.


Valve seals would be an extreme rarity.

MGB

It sounds like valve seals to me with 90,000 miles air conditioning running full time and just because the black smoke only shows up on start up.

Mythotical

Two words... "leaking injectors"

When you shut the car off the injectors are leaking and the fuel is pooling in the valve recesses in the pistons. When you start it that fuel is burned and poof... you get black smoke. This problem is only going to cause damage if they start to leak so bad that the fuel spills out of the recesses and runs past the rings into the oil pan thinning your oil and wearing out your rings. Just keep a close eye on your oil level. if your car seems to make extra oil you have a real problem.

P.S. You can also have your oil analyzed by a lab to determine if there is fuel in the solution.

LScowboyLS

smoke color guide:

black = fuel
grey/blue= oil or PS fluid or tranny fluid (they are all basically similar oil)
white = coolant


so smoke from valve stem seals would typically be gray/blue, but this is not an area where LS400 1UZ has any issues

LScowboyLS

A/C running all of the time does not have anything to do with leaking valve stem seals - in fact, you should run your A/C year-round for maximum compressor seal life

Gene01

Got it. Thanks!

MGB

My point on the A/C is, just extra wear on a motor much the same way extra pay load would be in a commuter vehicle or if pulling a trailer of some sort. It all creates accelerated wear!

LScowboyLS

the A/C system does not create extra wear on the motor, it just uses a small amount of extra fuel, the number of cold starts is truly what is responsible for wear.

even if it really did cause additional wear, seeing as how the 1UZ/3UZ engines can run 500,000 miles, using high quality oil and changing it religiously, do we really care if running the A/C its entire life brings that down to 475K miles?

Just moving to a lighter oil than 10W-30 makes a huge difference in engine wear (which occurs almost exclusively during warm-up) - so if wear is your worry, that is the direction to look in, not refraining from using the A/C, which will cause it to fail prematurely.

Mythotical

I agree. Cold starts are what allow full film lubricated parts to touch each other causing friction. Yes oil pressure may be high when the engine is cold but oil flow is low. The best way to mitigate this problem is to use the best cold pour point oils. 5w20, 5w30 and 10w30 all become 10wt at normal engine operating temperature anyway, so the best options are 5w20 and 5w30 but only if recommended in your owners manual. The A/C makes no difference, it just uses a little fuel and makes a little extra heat in the engine, but as a matter of fact an engine with a slight load on it especially when at idle will keep a little more steady pressure on the wrist pins and rod bearings which makes for less direction and or angle change causing even less wear than they would with no load, not to mention it makes an engine warm up faster. So actually having the A/C on will help things a little.

...one of the most basic and and yet most solid statements about the laws of physics in human history is that "there is no free lunch!" Just think about that for a while...

But seriously I am sure that my first post will make the most sense about what would cause black smoke at startup.