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Ladies and Gentlemen, I don't wish to open a "can of worms " but what is the consensus of opinion regarding oil catch cans and will we ever need them.

johnbiker7

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Hi John. There's already been a few threads on here about oil catch cans. Some swear by them. Others don't. Some like me don't see the point when a car is serviced once a year after covering only 3k miles.

To be honest I was actually looking into it and sought such cans but then dropped the idea like a stone. Main reason was the pipe to the PCV was firm stuck to it (I've got a new valve but can't get the old one off because of the pipe).

I suppose if your car does say 10k miles a year or more then I'd seriously think about one. Mind you perhaps another remedy is the valve carbon sprays you can get like seafoam. I'm going to try that a few days before my car goes in for its yearly service. 

Search the forum for oil catch can threads. There are a few.

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I don't actually think it is much of "can of worms" topic. I would rather group people into two groups here - the ones who have already done it and the ones who could not be bothered. I am in the latter. This is not because I think catch-can is not beneficial, but because for my car (when I had it) it was already too late.

So why would you need or want catch can? Well science is very simple - IS250 engine has positive crankcase pressure which is normal for piston engines, which means it needs Positive crankcase ventilation, which it obviously has. What is the problem with that? Well 4GR-FSE is direct injection engine and DI engines have issue with carbon built-up on intake valves as petrol (which is detergent) does not flow over intake valves, like it does on port injected engine. PCV valve on this engine at the same time goes into intake and here it has very obvious impact - it blows oily residue into intake which sticks to intake valves, which already are problematic area.

The catch can in itself catches the residue from PCV valve before it gets to intake and this prevents additional sludge buildup on intake valves. So that is the theory and it is correct. The practical issue - if your car has already done 100k miles without catch-can then you already have residue on your valves which is going nowhere (unless you planning to have engine apart and physically cleaning the valves) - fitting the catch can at this point is pointless exercise. 

If you have IS250 which is ~100k+ miles (which most of them going to be considering the age/average mileage) and you planning to keep it for 2,3 or maybe 5 years, then there is no point fitting catch-can. However, if you have low mileage IS250 which you planning to use for long time (maybe 10+ years) or to get it to million miles, then you definitely should consider fitting catch-can.

This is standard trade-off between cost, benefit and how long you planning to use the car. The longer you keep it the more beneficial it is.

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So based on that theory then I guess I should be in the ‘Fit one’ group! My 250 ( 2007) has just clocked 45k and I intend keeping it until it fails the MOT catastrophically on rust somewhere! ( hopefully a good long while yet)

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Yes... particularly considering your one is fully loaded unicorn car I cannot see you changing it soon 😁

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Linas,

I tend to agree with you. This seems to be a bit of a problem in the USA, presumably, because of lower octane fuel used over there. but they seem to run their cars to much higher mileages than we do . 200k + looks to be quite normal, and Lexus have sold a lot more cars in the US ,so the law of averages mean more reports of valve problems. My IS250 has done 112k and is running well,( there now i've jinxed it,).So I think i'll sit on the fence s bit longer. At least until the end of this hateful pandemic and warmer weather. Stay safe everyone.

Johnbiker7

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14 minutes ago, johnbiker7 said:

This seems to be a bit of a problem in the USA, presumably, because of lower octane fuel used over there

In the US you have a choice of fuel grades but Lexus require the same octane rating here in the UK as in the US - you need to make sure you factor in the different rating system used between the two countries when comparing.

However for the IS250 the type of fuel is irrelevant to carbon build up on the valves as the engine is only direct injection, no fuel ever comes into contact with them.

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I understand about the fuel differences, but reading posts on the US Lexus forum, quite a large proportion of owners run their cars on what they call regular gas. one result could be the ECU detects knocking, pinging as we used to call it when we had points and distributors, and retards the ignition. This could result in all sorts of problems. For example. to obtain the same performance, the driver would compensate by using a heavier right foot and therefor increasing combustion chamber temps. and because of more piston blowby increase crankcase pressure, resulting in more oil laden fumes entering the inlet manifold via the PCV . I know this could all be very hypothetical, but there must be some reason for the valve coking up problems they have over there, which you don't seem to hear of in Europe.

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@johnbiker7 I tend to disagree regarding fuel quality affecting blowby, if ECU retards timing then you likely going to get less cylinder pressure not more. There are several things which changes when timing is retarded (opening and closing of valves and spark timing), but in general the goal is to reduce the pressure - less pressure = reduced likelihood of knock ...  and less pressure means less blowby.

I think US problems are literally what you said in your earlier post - higher mileage. I still think their fuel is worse quality even after adjusting for for different rating systems (AKI vs RON), but they are not as bad as people may think and finally, I think maintenance quality is worse in US. Like dealership mechanics are less knowledgeable, uses worse quality oils etc. 

So overall they doing higher miles, and they maintain cars less well - so it becomes just logical that they have more problems in general.

As for your car at 112k miles I would say it no longer worth it, unless you planning to clean the valves somehow and you planning to keep car for 10+ years.

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5 hours ago, Linas.P said:

I think maintenance quality is worse in US. Like dealership mechanics are less knowledgeable, uses worse quality oils etc. 

I don't think that is true at all. Most people in the US cannot believe we go 10k miles between oil changes, they are changing every 3 to 6k miles. They have experts in auto transmissions in every town, we just have a handful in the whole country. Oil analysis is quite common in the US, almost unheard of in the UK.

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That is just my opinion, not a fact. 

I agree that compared with UK there are specialist just as good if not better in US, however the impression I got about standard dealership service quality is very bad. As such... again in my opinion... car owner in US have 2 choices - go independent specialist (which is expensive and can void warranty) or continue with standard dealership service (which is less expensive but rather patchy and only covers complete basics any repair hourly rate is excessive).

3-6k miles oil changes only applies to premium performance cars and only carried out by enthusiasts... certainly not common place. Small daily runabouts does not get such treatment. IS250 being small daily runabout car in amurican standards, it is only us in UK who thinks that 2.5L V6 entry-exec saloon is sporty and prestigious car.

By the way I was changing oil every 6k miles on IS250 as well, but that is just me and as you said in UK that is not common. 

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