Any drawbacks to an early MOT?
- Thread starter Dave D
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What, carry on driving a unroadworthy car? You could be prosecuted under the C&U act if caught knowingly driving an unroadworthy car. Despite what some say, an early mot failure will not void a previously issued test certificate.
I don't mean can I drive a death trap. I'm particularly thinking about emissions. I've had the car parked up a few months and smells a bit of soot after turning the engine off. I guess it could do with a few long runs before the test.
Why not take it on a long run, or a short hard run?
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A.K.A. An Italian tune up.
No problem driving that - it’s not something you’d ever get pulled up for or something that could ever be checked on the roadside. It’s not a nickable offence either as far as I know unless it’s belching out blue/black/white smoke and I do mean belching.
Could be a sticking injector, try some Wynnes in the fuel tank.
Stale petrol? Our sons 205 was laid up for a good few months when he was working in Poland. When he was coming home, I went round and got it started but the engine light was on. Gave it a good thrashing - still on. Went and topped up with fresh petrol, problem solved within half a mile.
Did that last Friday. Normally I drive my van like an old lady on the way to Sunday church. But it get's an annual 'drive it like you stole it' blow out and motorway mobile decoke just before the MOT. When I started the process (making sure it's properly warmed up first), flooring the accelerator when pulling away produced clouds of black smoke. Normally there's no smoke when driving. But after doing this a couple of times and it didn't happen again. A warp factor nine, 15 minute motorway fast lane blast (get out of my way!!!), and the van arrived at the MOT station cleaned out and fully heated up. Works every time, as my readings were nowhere near the limits.
I do chuck some Redex injector cleaner in the tank occasionally to help things.
I'm a great believer in the efficacy of the "Italian tune-up" - especially for diesels! Mrs. Avocet used to drive hers very gently (still does, in fact). I'd notice a bit of black smoke in my mirror when I borrowed it and booted it. However, this would clear up after a couple of bouts of hard acceleration. My theory, is that oil mist collects in all the induction tubes and the intercooler. It condenses on the walls, into liquid oil again. Driven gently, you don't get the air flow rate through the inlet tract, so more an more of it collects. When you run at maximum power, the engine sucks a huge volume of air into its inlet, and "scours" the inlet tract. Most of the horrible, sooty oil gets dragged through the pipes and into the engine, where it is burned. After doing this a few times, it will have sucked as much as it can, through the system and is fine again. The smoke goes away, even under hard acceleration. Ideally, you want to do this for at least 20 or even 30 seconds at a time, but that's quite hard to do without losing your licence, unless you can find a long, steep hill and / or a heavy trailer. Her previous car was a T30 Nissan X-Trail. The owners' forum was full of takes of choked-up inlet manifolds and EGR valves. So much so, that at 100,000 miles, I got worried enough to take the EGR valve out and have a look at hers - Nothing! Just a fine layer of dry, black soot on the walls! Doing the "Italian tune-up" once a month or so, I've never had a problem with an EGR valve or blocked inlet manifold
I checked mine at 90K, and it was badly choked, as was the intake - it can't have been doing the emissions, or consumption any good, so I decided to clean it all up and bypass it. It is tested every year, on the MOT, and always now comes back with a figure to low to register.
The problem with bypassing the EGR valve, is that it increases NOx emissions The car will still fly through its MOT, because the MOT test can't even detect NOx emissions, but that's really a shortcoming of the MOT test
The EGR was a botch, added on to have diesels meet emissions requirements. The work fine when new, but can cause major emissions issues later in the engines working life. Really, the EGR and intake, ought to be marked up as a regular service item, but no manufacturer would dare to add it to the list - the result is excessive consumption, poor performance, and clouds of smoke out the back.
To be honest, I've never had a minute's bother with one, even well beyond 100,000 miles. Very much a "fit and forget" item in my experience. However, the engines do need working hard, periodically. I inherited a 2001 Freelander from my sister. She was going to scrap it, but I needed a tow car. One of the problems was smoke - (boy, did it smoke!) on acceleration. She always hated revving it, never went over 3000, and always drive gently. It has about 150,000 on it at the time. The inlet manifold and EGR were full of oily, sooty gunge, which I scraped out, then washed. It's been fine ever since! Currently being used by my dad, approaching 170,000 miles now.
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