M.O.T. and diesel vehicles.

[t-tony]

As if it’s a “new” thing?

MSN

www.msn.com

I read this on MSN, they report this as if it is a new thing. In an MOT station there is a Notice Board where it tells diesel owners about the need for maintenance, especially timing belt history. The customer should be asked about it at the time they book an MOT test. But, how many are? Where I used to work they haven’t bothered to ask this question for years mainly because people who own older diesel vehicles simply say, “I’ll risk it”. It is just too much trouble to get into the discussion at the time of booking it in so they just don’t bother. Next time you book a test the first or second question ought to be, “Is it a petrol or diesel”.

Tony.

 

[Duncodin]

I can understand an mot station not wanting to test a really bad looking car for fear of it breaking during the test and them being accused of breaking it.

But why pick specifically on diesels? Are diesel car tested differently? I mean do they go through a different test procedure that would make their timing belt more critical than that of a petrol car?

 

[t-tony]

Totally different emissions test.

Tony.

 

[Duncodin]

Totally different emissions test.

Tony.

What i mean tbough is is a diesel more likely to break during the test? Sorry. Not being argumentative. I'm genuinely interested.

 

[abh29]

Can any station carry out MoT on an electric car.

 

[t-tony]

What i mean tbough is is a diesel more likely to break during the test? Sorry. Not being argumentative. I'm genuinely interested.

To test a petrol engine you have to hold steady engine revs just below 3,000 rpm usually for half a minute or so.
A diesel however, having determined that there is sufficient oil in the engine if it has a dipdtick, (another reason to refuse to test), has to be revved to the red line ( 3 times if it doesnt pass on the first effort), which puts maximum stress on the cam drive train. In the case of a rubber belt possibility of failure and consequently severe engine damage.

Tony.

If you have a VAG car they will not rev that high due to the "fix" which cost VW a lot of money in the USA.

 

[Duncodin]

To test a petrol engine you have to hold steady engine revs atjust below 3,000 ram usually for half a minute or so.
A diesel however, having determined that there is sufficient oil in the engine if it has a dipdtick, (another reason to refuse to test), has to be revved to the red line ( 3 times if it doesnt pass on the first effort), which puts maximum stress on the cam drive train. In the case of a rubber belt possibility of failure and consequently severe engine damage.

Tony.

If you have a VAG car they will not rev that high due to the "fix" which cost VW a lot of money in the USA.

Now I understand. Most petrol engines spend a lot of their time way over 3000rpm. My MB GLA, on the other hand, is red lined at around 5000 (I think) but rarely gets near 3000 even at motorway speeds. I don't think I've ever had it over 3000 so Red Line is way out there.

 

[Peter1450]

My Caddy used to drive the tester insane as it would take him twice as long to do the test as it would take so long to get upto temperature as per what Tony says it won’t rev above 3k !

 

[Jack Ratt]

I had to provide proof of date of timing belt change before my garage would agree to test my diesel Saab. As luck would have it my Saab was a one owner vehicle with full service history and with only 50k on the clock it was a recent change.

 

[t-tony]

My Caddy used to drive the tester insane as it would take him twice as long to do the test as it would take so long to get upto temperature as per what Tony says it won’t rev above 3k !

I discovered, quite by accident, that VAG vehicles will rev to max rpm in certain conditions. The yard at Tanvics sloped down towards the workshop and if you allowed the vehicle to roll down the slope (in neutral) at a slight turn on the steering (so that the steering angle sensor didn't think the car was parked with wheels straight ahead), with these 2 conditions met the engine will rev to the red line. This was the testing "fix". If the the vehicle has the parking brake on and wheels straight ahead the vehicle thinks it is in testing mode and cuts the throttle out at about 2,500rpm.

Tony.

 

[Duncodin]

I had to provide proof of date of timing belt change before my garage would agree to test my diesel Saab. As luck would have it my Saab was a one owner vehicle with full service history and with only 50k on the clock it was a recent change.

My diesel car has a timing chain. I know chains aren't perfect but they are continuously lubricated so should last a while longer than a dry belt. You'd think.

 

[t-tony]

Very few diesel engine have specified change interval for a timing chain. The early E89 4 cyl. Petrol turbo engines (fitted in other cars too) had a bad rep. But that has been rectified now.
Some engines (Ford) run their cambelts in oil would you beleive!

Tony.

 

[Peter1450]

Similar on the caddy , they run a belt to the oil pump in the sump for some strange reason, probably employed the BMW guy who put the inaccessible water pump in the Z4