jay90011

iTrader: (23)

@ KillaIS250
My car is at Lexus of Santa Monica. I think u would have to have a history of your car having the issue. I was front of the line for the fix because after 3 top engine cleans and 4 engine stalls. They called me the moment the parts were in.

fjascione

Im not an expert but I dont understand how this "engine overhaul" will fix the carbon build up. Is there some who could remotely explain the theory behind changing our engine parts?

Thanks

meangene

iTrader: (10)

I'm waiting on my dealership to get the parts to send my car in. I'm honestly not sure if I want to do it...

hades281

I have no idea why piston rings are the cause for the carbon buildup problem in our cars... mostly because these cars are not known to use oil, and used oil analyses don't indicate a wear problem.

Let me preface this by saying I'm not a mechanic, but I am a mechanical engineer with a general understanding.

I would understand if the cars were using excessive amounts of oil - worn or "low tension" piston rings could allow higher than normal amounts of oil into the combustion chamber. The combustion byproducts, due to the internal EGR, would ultimately pass over the intake valves and/or accumulate on the piston tops. (Would deposits then form? I don't know.) Do keep in mind that EGR passages routinely become clogged in all kinds of engines where the EGR circuit is external (small passages which are easy to clog), indicating that vapors caused by exhaust gas recirculation can cause carbon to accumulate.

The Cadillac Northstar engine, for example, is a "low friction" engine that used low tension piston rings. This caused oil consumption around 1 qt / 1000 miles! Of course these engines were not direct injection - so some fuel did wash over intake valves, but overall these engines did not need decarbonization.

What I really want to do is read the TSIB, and I also wonder how effective the BG direct injection induction cleaning service really works in our engines. Like others I am not excited about my engine being torn down by the dealership.

KillaIS250

iTrader: (1)

Hmmm now that you mention it....i'm not sure i'd want the dealership tearing down the motor either. :/

chikoo

+1.
Good thought process there.

Our engines are GDI high compression engines. Is it possible that the folks with more trouble than usual indeed have some issues with their piston rings??

chikoo

>>I also wonder how effective the BG direct injection induction cleaning service really works in our engines. Like others I am not excited about my engine being torn down by the dealership.<<

I am not sure about that either, but I will tell you that I am a believer of the BG-44K product now.
For over 6 years my RX idled horribly and Lexus said "thats normal". All high mileage RX are like that.

I tried techron, gumout, etc all these years but no effect.

Earlier this year I purchased the expensive BG-44K and poured it in the tank of my RX.
Voila! The vibrations are gone.

APynckel

The reason for it is this; a more loosely toleranced engine is going to have less interference. Less interference between the piston and the cylinder wall means less friction, and thereby more free movement and less power loss. This attributes to more power, but also more blowby and thereby crankcase pressure. The crankcase vapors (burnt oil and other hydrocarbons from the combustion process) are reinjested by the engine through the PCV system and then deposit on the valves (a high turbulence area) when they fall out of suspension. Coupled to the heat of the engine, these vapors solidify into carbon deposits (coking) on your valves and will flake off causing problems in the combustion chamber, which is what causes the hesitation and stalling.

In a non-direct injected engine, the gasoline being sprayed into the cylinder head acts as a solvent to clean the valves (save you are using clean gasoline with a high octane rating) and prevents the coking of the PCV oil vapors onto the seats. This is the only way to keep the valves on the intake side clean. You can seafoam your car, but good luck finding an induction point that will atomize the chemical finely enough to not leave puddles in your intake manifold and/or hydrolock your engine.

As far as your point about the external EGR's clogging, that is because of the rapid cooling the exhaust gasses are subject to when they leave the head. It makes the unburnt long carbon chains cool and coke thereby clogging the tube over time. Same concept as what is going on with our engines to an extent.

Also, blowby doesn't necessitate oil burning. Oil doesn't burn because of blowby, oil burns in the combustion chamber when it comes down from the head (bad valve seals), or when the rings don't scrape it from the cylinder walls properly, but there should be minimal loss from the latter.

Chikoo: There is simply no chemical you can pour into your gasoline to clean your valves, because the injection process in these engines doesn't touch the valves. What happened with you using the additive was it broke down the solid matter in your cylinder, and pushed it out. It didn't take care of the rest of the coking on your valves.

There are only 2 ways you can combat this problem. 1) tighten up the tolerances of the piston / cylinder and have some detrimental power loss from the increased friction or 2) install a catch can between the PCV source and your intake pipe to catch the oil vapors before they have a chance of getting to your induction system.

hades281

But there are no signs of (an unreasonable amount of) blowby. These are high compression engines... if the engines were losing compression, then I would agree there was a problem with the compression rings and here I would expect blowby. If the engines were consuming oil, I would agree there was a problem with the oil rings. If there were high wear metals in UOAs taken for these engines, I would suspect something there too.

The engines already achieve a 12:1 compression ratio. How much better do they expect to seal against the cylinder?

APynckel

The sign of blowby is that there is oil vapor depositing into liquid oil in the intake manifold. Having that high of a compression ratio typically causes blowby. Go do a compression check on your engine, I can almost promise that you won't hit 100% across the board what the engine is supposed to in terms of pressure. That means there's blowby. There is ALWAYS blowby in an engine! That's because you cannot tolerance dynamic parts tighly. They have to be loose to allow the parts to move. Blowby != burnt oil.

Tell you what, I'm going to fab up a catch can here and run it to see how much fluid it collects over time.

hades281

Of course there is always blowby. (When I said "no signs of" I meant of an unreasonable amount. Typically nobody mentions blowby in an engine until it is excessive.) These are the points I am making here:

1) They will never make blowby zero;
2) There will always be some EGR flow;

Thus you will always have some oil vapor / combustion byproducts in the intake;

3) There is no indication in UOAs that the rings, or engine overall, has wear problems;
4) Maintained compression suggests properly functioning compression rings;
5) No / acceptable low oil consumption suggests properly functioning oil rings;
6) This engine is very, very easy on oil which further suggests good ring seal;

So what is Lexus trying to accomplish here and what will be the result? One main advantage of the GDI technology is to run higher compression. The fuel injected directly in the cylinder has a cooling effect that prevents preignition.

If they replace the pistons or the connecting rods, they can increase the compression ring tension and compensate for the compression ratio with the modified piston stroke or volume.

If I was Lexus, I would look into modifying the intake to somehow include or utilize additional fuel injectors -- maybe add one or two to the surge tank that can spray continuously if the flow would be enough to maintain clean valves. Or, they could consider an easier cleaning procedure (something like the BG Inject-a-flush, if it works) and offer it free to customers every 30k miles. If they don't want to tear into the fuel system, put a water injection kit and a reservoir -- similar to a DEF / urea tank on diesel engines - that is refilled for free by the Lexus dealer.

APynckel

Well, that's why I'm all for just adding a catch can to reduce the amount of PCV vapors that reach the intake valves.

There are a few misconceptions in your analysis, but in the end, there are deposits forming on the intake valves and it's coming from somewhere. The only thing that can cause it is the PCV system. Oil vapor doesn't come from the exhaust.

This isn't a wear issue, it's happening from the start. So it doesn't matter that there's no wear signs or loss of compression, because everything is continuing to act the same as the day it left the lot. The vapor is simply depositing over time.

hades281

Post pics of your installation - I am curious to see what you find here. I haven't taken a close look at the PCV system on these cars. I wouldn't rule out the internal EGR on these engines as a contributor. I think the idea here is that some combustion products are "puffed" back into the intake and drawn back in.... Even the tailpipes have a stubborn carbon coating that doesn't easily come off.

Further, the previous Lexus cleaning procedure which uses GM top engine clean seems to target the piston tops more than the valves. In that procedure, 1 oz. of cleaner is poured into each cylinder and left to sit for a while. Sure, some will be splashed onto the valves indirectly but that will drip back into the cylinder. Perhaps the carbon buildup is not limited to the valves.

If you do a google search for "Engine oil GDI engines" you will find a discussion where people attempt to use Marvel Mystery Oil to clean the valves. Here they point to EGR as well. I copied and pasted the response from a MMO representative:

chikoo

How about using a medical syringe punched into the rubber intake tube hooked to a bottle of MMO / GM top end cleaner? The MAF is anyways @ the airbox.

freeflight

Sounds like an engine design flaw.
Does this mean every IS250 will eventually have this problem? How much would it cost to repair it out of warranty?