Dervs and emissions tests

[Dick Cheeseburger]

I took the WoganWagon to Hi-Q earlier, armed with a couple of parts as well as oil and filter, and the agreement they'd fit my supplied parts, which works well for me. Whilst I was there, a couple of the lads were putting a Pugrot 307 through its MOT. When it came to emissions, they revved the living shit out of it, and held it there for what seemed like ages, but was likely 10 seconds max.

When I get my own dervs tested, I know the fellas (I go to a different garage for testing), but always assumed they did the test fair and square, with the exception of maybe the odd borderline advisory. With my car, they tend to give it around half throttle and don't seem to hold it there for long either. Am I wrong, or do testers not need to rev the crap out of the engine on the test now? Whatever the case, the lads testing the 307 seemed to think it was quite amusing.

[garbaldy]

The tester I use doesn't like reving the engine either, I guess a quick rev at half throttle will be better for the emission test as well.

[scaryoldcortina]

You are supposed to floor it, and hold it there until the machine tells you to stop. Obviously, many testers are a bit wary of doing this to random old chod that might decide to shit itself in the test bay, so the usual thing is to rev it reasonably gently until you get a reading instead.

 

 

There is supposed to be a new gas based test for diesels coming along soon because many modern ones won't even let you rev them in neutral and also don't emit enough smoke to get a reading.

[garbaldy]

My guess is many testers who actually like cars don't want to rev any engines that much not just old chod,

As said the tester I use tests my moderns too

[scaryoldcortina]

Old chod=any motor vehicle old enough to require annual testing.

[garbaldy]

Crickey next you will be telling us a retro car is anything older than three years.

[forddeliveryboy]

Revving like that doesn't do much for autoboxes, either. My tester generally gives as few revs as possible, for as short a time as possible. He wouldn't consider holding one to its limiter for seconds on end, ime.

 

I thought after many wrecked engines, the authorities had changed the rules so you don't rev a diesel like that. Another reason to avoid large garage chains.

[richardmorris]

I've heard from my garage in the past that the testers like to rev the diesels hard, and that as such I should get the cam belts done sooner rather than later ( this was on my cx DTR turbo).

[scaryoldcortina]

The trouble is that because the manual says it must be done then to conduct a proper test you HAVE to rev it. Your only other option is to abort the test if you believe that conducting the smoke test would damage the engine. That's what it says, and that's what DVSA (VOSA) insist on. If they catch you deliberatly ignoring the test procedures then you get points and could lose your licence over it.

 

This is why I'm not admitting anything.

[garbaldy]

maybe the powers that be should start listening to the mechanics instead of being arogant so and sos

[Dick Cheeseburger]

I thought after many wrecked engines, the authorities had changed the rules so you don't rev a diesel like that. Another reason to avoid large garage chains.

This is what I thought I'd heard. If I enjoyed driving with the engine bouncing off the rev limiter on a regular basis, I wouldn't mind so much. Whatever the case, it's confirmed to me that I'll continue to get my car mot'd at the same place I've used for a few years now. I can't see new dervs being allowed to be sold for much longer tbh, so I'll continue to enjoy my Victorian influenced soot making machine while I can.

[dollywobbler]

maybe the powers that be should start listening to the mechanics instead of being arogant so and sos

 

Maybe the powers that be couldn't give a monkeys whether some elderly motors suffer engine failure during the test...

[garbaldy]

Maybe the powers that be couldn't give a monkeys whether some elderly motors suffer engine failure during the test...

 

They would be if they where the ones who had to explain to the punter that they cant drive home due to engine explosion.  

I cant believe that its just elderly motors that are at risk either.

[scaryoldcortina]

http://www.transportoffice.gov.uk/crt/repository/Diesel%20Smoke%20Test%20-%20Info%20Card.pdf

[Richard]

They suspended the smoke test for a while soon after it was introduced, because of engines blowing up.

[sierraman]

If your engine can't hold being revved hard once warm for 10 seconds, the MOT is the least of your worries.

[garbaldy]

If your engine can't hold being revved hard once warm for 10 seconds, the MOT is the least of your worries.

 

engines are not designed to be revved to the limiter without being under load though that is the issue I believe,

[forddeliveryboy]

http://www.transportoffice.gov.uk/crt/repository/Diesel%20Smoke%20Test%20-%20Info%20Card.pdf

 

quote, "Your engine will not be held at full speed for any length of time". Typical civil servant speak.

 

Surely it's widely acknowledged that engines aren't intended to rev their ends off with no load on them?

[Tamworthbay]

The garage my father in law uses for his mots have a big sign on the mot bay warning that diesels will be abused in the pursuit of an mot. My mot guy seems to have more brains and is sensible about it.

[mat_the_cat]

engines are not designed to be revved to the limiter without being under load though that is the issue I believe,

 

I can't see why revving with no load is *more* damaging than with a load?

[twosmoke300]

Engine is accelerating far quicker than it ever would on the road so more likely to jump or break a belt

[cros]

They used to rev to the limit for the time specified by the machine at my local mot garage so after the first time I wound the pump control stop screw in for the test. I've had all the shit like 'if your engine is in good condition it won't hurt'. I've now got 4 diesel pre '59 vehicles so I avoid the horrible ordeal and get pleasure from no longer having to pay someone to abuse them.

[mat_the_cat]

 

Engine is accelerating far quicker than it ever would on the road so more likely to jump or break a belt

 

Fair point. But if the throttle is fed in gently rather than mashed to the floor, is there any other reason why no load is bad? I don't have any worries about revving to the red line once warm on any of the fleet, so the MOT test has never held any worries for me.

 

Might ask them to go gently on the van next time though, as it's only got a few hundred miles on the new head so I don't consider that 'run in' yet...

[forddeliveryboy]

I'm never happy revving gearboxes (even manual ones) fast under no load, either. As with an engine, there's the possibility of 'chatter' and vibrations which don't exist when everything is leaning against a load. Autoboxes are well known to be averse to this sort of treatment.

 

A while ago I had an old car with its original white metal bearing bottom end, with several hundred thousand miles under its belt and a little lash in the big ends when cold - add in a long stroke/longish rods and I was always nervous at 60-70 with an engine which wasn't heated right through. Top speed was about 90, above 75mph it was pulling hard enough not to worry me. The start of most longer, faster journeys included a 3 mile stretch of dual carriageway - just right to heat things through. Once warm, it was as sweet as a sweet thing, I completed several very fast trips in it and it always sounded exactly the same the next day.

 

I sold the car to a mate and told him all about the issue, which he supposedly took on board. But he disregarded my suggestion of engine oil and rang up an 'expert' who worked on the PR team of an oil supplier for old cars. I suspect nasty oil and sitting at 70mph on a long motorway descent did for it - the engine was not warmed through, either. It stuck a rod through the block.

[michael1703]

You are supposed to keep emission printouts for 3 months,you only get a printout if the emission test is conducted as the machine dictates. Temperature probe down the dipstick tube,60℃ min temp and rev it until the smoke head detects something up its hole. Some moderns will only rev to about 2500rpm at standstill and you tend to get "acceleration detected" at about 4000rpm. I spend as much time as needed to get a reading but if you were employed by a fast fit company you've got a gun to your head by your boss you haven't got time to do it carefully

[Dick Cheeseburger]

I'm glad it's not just me that cringes when hearing a derv being hammered and held on the red line. Dervs especially sound bloody horrendous when been given beatings, and it's not pleasant to listen to. I liken it to your wife coming back from the gynaecologist, explaining that he 'had a quick go' to see what the problem was.

[beko1987]

when I first showed the zx to my mot man he asked when it last had a cambelt, then smiled when I said very recently and he floored it all 4 or whatever times!

 

Id say its good to floor it, mine blows bluey smoke out when held, which it never does day to day so I know I havebt got to worry about that yet

[forddeliveryboy]

when I first showed the zx to my mot man he asked when it last had a cambelt, then smiled when I said very recently and he floored it all 4 or whatever times!

 

Id say its good to floor it, mine blows bluey smoke out when held, which it never does day to day so I know I havebt got to worry about that yet

 

Blue smoke when held at full chat, no load? That may be the piston rings not behaving as they're designed to. 

[michael1703]

Or the weird mix he runs it on

[castros_bro]

They used to rev to the limit for the time specified by the machine at my local mot garage so after the first time I wound the pump control stop screw in for the test. I've had all the shit like 'if your engine is in good condition it won't hurt'. I've now got 4 diesel pre '59 vehicles so I avoid the horrible ordeal and get pleasure from no longer having to pay someone to abuse them

 

Did you used to work for VAG ?