Inlet valve carbon build up

johnatg · February 16, 2016

This is a topic we come back to now and again.

Just a heads up really - there's an interesting article in 'Car Mechanics' this month (March 2016) about dealing with the subject (Decoking modern engines). Apparently Dr Helmut Leonhardt of Shell Lubricants has done a lot of work on the inlet valve problem on Direct Injection engines (including his PhD) and puts it down to Viscosity Improvers in the oil - the carbon comes from oil which gets into the inlet tract via the crankcase breather system and EGR valves (no EGR valve on IS250s though).

The article covers cleaning techniques including walnut shell blasting (there's a photo sequence of it being done on a Mini) and TerraClean.

So there you go if you're interested.

Shahpor · February 16, 2016

This has become an interesting issue.

I also saw mention of crankcase re-breather systems and EGR causing issue, but I thought the main culprit was the fact that direct injection fuel system no long swirl fuel over the valve, which used to clean it?

I have seen people debate whether an oil catch tank benefits the car or not. I am not so sure it does myself. Obviously, EGR valves are the devils work and improve the car in many ways with their removal.

The videos showing walnut shell blasting are funky. I wonder how someone came up with the idea of using walnut shells to clean engines? The only thing about it is that I wouldn't be happy doing it with the head on the car. The video I saw had a vacuum hose down the bore while it was being done, but surely the shells are still abrasive if left inside?

I admit I am tempted to buy a bore scope to see the state of my valves now

johnatg · February 16, 2016

Yeah - the problem was actually always there but the carbon was washed off when fuel was injected before the valve.

Walnut shells are soft compared with the bore etc, so they don't cause any abrasion to the metal, either in the valve area or bores. The technique involves setting each piston to TDC which fully closes the valves. Then the ground up shells are blasted in and vacuumed out. The operator checks the results and does it again if necessary, and also checks that there are no shells left in the inlet tract. Then moves on to the next cylinder. You need an adapter tool which incorporates a nozzle injector and vacuum extractor and it has to fit the inlet tract exactly - ie a different adapter for each car model. Do they have them for IS250s??? It's not a cheap process - the article quotes from £299 for a 6 cyl BMW so maybe an IS250 might be similar.

The conclusions about TerraClean are mixed - ie no objective evidence and TerraClean are very cagey about how it works. They are supposed to be supplying proper evidence later this year.

I've got a USB endoscope - keep intending to have a look at the backs of my valves - you need to insert it down the inlet tract, not into the bores - you wouldn't be able to see the valve backs from the combustion chamber side.

Shahpor · February 16, 2016

Funny how the drive for efficiency has actually made the internals of the engines dirtier.

Well, I suppose if the Walnut shell blasting can be done with the head in situ then it might be a worthwhile endeavour. Although there would have to be a hell of a lot of carbon to be worth spending £299.

On the face of it, the TerraClean looks to be a better system, but since you can't see the results directly, I am not so sure. I like the idea of being able to look down the inlet to see the results. Although, according to the episode of Wheeler Dealers where they did it to the XK8, it works and only costs around £70.

Sorry, I actually did mean an endoscope, just couldn't remember the name of it

I wonder if this is going to become a much more widely spread problem in the years to come?

Verbout · February 16, 2016

I've watched loads of videos on YouTube about this "modern phenomenon".

One video that I cannot find at the moment shows about a dozen products being tried on inlet manifolds, none made any considerable mark on the carbon build up.

Isn't Terraclean injected via the fuel rail, so will not have an effect on the backs of the valves in cars that have direct fuel injection?

johnatg · February 16, 2016

The CM article shows pics of the Mini (1.6 'Prince' engine in a Cooper S) inlet valves before and after treatment - before they were well carboned up (this engine suffers particularly badly apparently) - after, they were spotless and the tract walls nearly so.

To be fair the TerraClean method comes under the heading 'Chemical combustion chamber cleaning' so I guess that would be irrelevant as far as inlet valve carbon goes. It does show impressive results for other processes - they have a technique for cleaning EGR valves which involves connecting the tool to the EGR cooler. (Pictures shown in the article) They have DPF cleaning techniques too - both might be of interest to our diesel friends!

Shahpor · February 16, 2016

Quite right, TerraClean uses the cars own fuel injection system to clean, so it wouldn't be as effective on direct injection cars.

Ooo, EGR and DPF cleaning? Where do I sign up?

I was going to say that throttle bodies would also be a good place for this method, but since it isn't exactly hard to get to these and clean them by hand, I don't think it would be worth it.

Do you guys think this will become more mainstream, like de-coking of heads used to be in the good old days?

I must admit I am very curious now about the state of my inlet valves. Gonna go have a hunt for an endoscope

Verbout · February 16, 2016

1 hour ago, Shahpor said:

Quite right, TerraClean uses the cars own fuel injection system to clean, so it wouldn't be as effective on direct injection cars.

Ooo, EGR and DPF cleaning? Where do I sign up?

I was going to say that throttle bodies would also be a good place for this method, but since it isn't exactly hard to get to these and clean them by hand, I don't think it would be worth it.

Do you guys think this will become more mainstream, like de-coking of heads used to be in the good old days?

I must admit I am very curious now about the state of my inlet valves. Gonna go have a hunt for an endoscope

Don't forget the lube.

toffee_pie · February 17, 2016

Without reading or delving into this much, I would imagine this is more relevant for diesels with all the particle filters and egr valves they have to deal with. Modern petrol engines IMO don't need any additives at all, regular oil changes is sufficient for them for the life of the car.

johnatg · February 17, 2016

It's getting to b a major problem with petrol engines but diesels are worse. Most engines (both petrol and diesel) have EGR valves (although thankfully not IS250s). But oil vapours get into the inlet tract via the crankcase breather anyway. The culprit identified by Shell for the severity of the carbon build up is Viscosity Improver - that is not a DIY additive but is put in the oil during manufacture to provide 'wide band' viscosity - ie 10W-30, 0W-40 etc. The bigger the difference between the two numbers the more VI is required. It certainly helps to change the oil much more frequently than recommended.

The problem doesn't seem to have hit us IS250 owners in UK too much but there are a lot of reports of it in US.

The CM article referenced shows intake valves in a Mini Cooper S (petrol) engine at 77K miles - they are in a dreadful state before walnut shell cleanng.

Shahpor · February 17, 2016

Although by no means a qualified source, the following article seems to explain quite well the problem:

http://www.aa1car.com/library/intake_valve_deposits_gdi_engines.htm

As you can see, this is an issue that effects all modern cars, not just diesels.

Verbout · February 17, 2016

Some of the mod boys recommend Mr Muscle, used especially on the turbos, but also squirted down the throttle body to clean the backs of the valves.....EEK.

I would try it,,,,,,,on someone else's car

Jules PF · February 17, 2016

2 hours ago, johnatg said:

It's getting to b a major problem with petrol engines but diesels are worse. Most engines (both petrol and diesel) have EGR valves (although thankfully not IS250s). But oil vapours get into the inlet tract via the crankcase breather anyway. The culprit identified by Shell for the severity of the carbon build up is Viscosity Improver - that is not a DIY additive but is put in the oil during manufacture to provide 'wide band' viscosity - ie 10W-30, 0W-40 etc. The bigger the difference between the two numbers the more VI is required. It certainly helps to change the oil much more frequently than recommended.

The problem doesn't seem to have hit us IS250 owners in UK too much but there are a lot of reports of it in US.

The CM article referenced shows intake valves in a Mini Cooper S (petrol) engine at 77K miles - they are in a dreadful state before walnut shell cleanng.

I was/am having the same issue with my Is250. The problem is with the GDI engine design, petrol no longer washes over the valves, so the detergents in fuel do not clean them. Lexus have addressed the issue with a GDI and conventional port design on the 350. You are correct Terraclean or hydrocleaning will not help the carbon issue.

I have been experiencing heavy oil loss (easily 750ml per 1,000 miles). After a lot of investigations, it was determined I had no leak, thus the oil was being burnt in the combustion process. I have always been concerned by the amount of exhaust I can see emitted, and would often compare to other cars at traffic lights, for instance. Here is how I addressed the issue, I believe I have 'fixed; it. Early days, but it looks hopeful.

1) use a good quality valve cleaner from Forte, Liqui moly or Wurth. Before changing the oil. These must not be added to fuel, that is useless on the GDI engine, instead they are to be sprayed into the air intake, so that the cleaner mixes with air in the manifold. I have also used seafoam, but to be honest, I didn't find it particularly effective. The one that seemed to make the most difference was the Liqui Moly valve cleaner. The car seemed much better afterwards, purely gut feeling, no scientific data.

2) Change the PCV valve at least every other service, so 20k miles. Lexus have no maintenance schedule for this valve. That is a major oversight. This valve works on a similar way to an egr valve, passing unburnt gasses and vapours (inc oil) back to the intake manifold to be burnt. It is part no. 12204-31040 and is £28 in the uk. I ordered one from the states for less than half. I wasn't due to service it for 2 weeks so could wait the 8 days. I actually ordered 2, for less than the price of 1 in the UK, and I don't feel ripped off!! The old valve, when shook, was hardly making any noise, ( it should rattle). The new one was much better, Upon fitting, the difference in the car was immediate. Barely noticeable exhaust smoke!!

3) Use a fully synthetic oil with a low NOACK rating. This is the amount of oil that evaporates at a given temperature. This is given as a % and the variance can be be huge. I am using Mobil 1 ESP 5w 30, which is rated at <6%. Other oils, such as Comma Syner-Z 5w30 are <13%, some are higher. Mobil actually recommend a different oil for our cars, but it has a high NOACK of <13%. Therefore these higher NOACK oils will be burnt off at a much higher rate than the Mobil 1 esp.. Lexus changed the oil spec to 5w20, but this was purely for economy reasons. This oil is much more difficult to source, so I've stuck with the 5w30.

I have only completed 500 miles thus far but have not shown a loss at all on the dipstick and the excessive exhaust smoke is a thing of the past.

johnatg · February 17, 2016

Interesting - did you use Liqui-Moly MTX Carb. & Valve Cleaner rather than the throttle valve cleaner?

I have cleaned the PCV valve on my MX-5 from time to time ( I guess partly because it's obvious and easy to get at) - I squirt WD-40 into it. A good deal of gunk comes out - but I don't think it has got to the point of not rattling at all - but it rattles better after cleaning!

Must try that with my IS250.

It doesn't seem to be very easy to find NOACK ratings - I use Dexos2 (GM branded, so sold as Dexos2 product rather than licensed) - I can't find a NOACK figure at all for the Dexos 2 spec.

Shahpor · February 17, 2016

Speaking of oil, I have to have my car serviced by a Lexus dealer, so does anyone know what oil they use?

Jules PF · February 17, 2016

With Noack rating you have to ask manufacturers. They have the data and will take a day or so to email you back.

I used quite a few seafoam, holts but recommend liqui moly valve cleaner. Pcv should definitely rattle when shook. If not it's faulty, however one that does rattle does not mean it's working! Hence why I would recommend simply changing it, it's cheap enough if sourced from rockauto in the states for instance.

Brechin Slate · February 18, 2016

Interesting to read about the ground walnut shells. We used this technique (carbo blasting) to clean gas turbine blades on my previous warships. Ostensibly it was to remove the salt deposits off the compressor stage blades and then the shells were burned up in the combustion chambers. Although there was a dosing pot on the gas turbine itself, the preferred method was to throw the shells 'at a measured rate' down the air intakes on the upper deck. Great in theory but once the stoker picked the wrong intake and pebble dashed the boys in the boiler room who were standing under the fresh air vent to stay cool. We used to call the process 'feeding the chickens' because that's exactly what it looked like!