Question for you diesel owners

[whiskychaser]

Coincidence or solidarity, but I often end up parked next to a guy who owns a '95 525 diesel. He told me today it threw a fan belt on the way to work. He said there is some sensor on diesels that cuts the motor to prevent them being damaged if they start to get hot. Thats why he ended up coasting onto the hard shoulder of the motorway. I am sceptical to say the least. But I'm always willing to learn :-) Any comments?

[Ferret]

Coincidence or solidarity, but I often end up parked next to a guy who owns a '95 525 diesel. He told me today it threw a fan belt on the way to work. He said there is some sensor on diesels that cuts the motor to prevent them being damaged if they start to get hot. Thats why he ended up coasting onto the hard shoulder of the motorway. I am sceptical to say the least. But I'm always willing to learn :-) Any comments?

I'd say this is probably crap, I dont think any car is allowed to make a decision to just cut power. Remember the uproar the cutting out 206's caused not so long ago as they were suddenly losing power on the motorway?

The car would be downright dangerous if it did that, from what I remember you have to be able to keep running the engine till it seizes, as after all it's better to have a cheap seized engine than a smeared car on the motorway (hugely expensive when you block the motorway doing that :) .)

[whiskychaser]

I'd say this is probably crap

My thoughts in a nutshell :D

[Tiger]

Diesel engine runs without electricity so alternator will not be an issue unless it is nighttime and your battery is running down for light. However, there is an issue with waterpump as it is not rotating anymore since the belt is broken... would lead to overheating... Just like any gas engine car... engine will run until seized...

[Ferret]

Diesel engine runs without electricity so alternator will not be an issue unless it is nighttime and your battery is running down for light.

Not so on the E34 M51 engine, which uses electronically timed diesel injection systems.

[Tiger]

Ahh... so than a broken belt would shut the BMW diesel engine down when the battery runs low.

[Ferret]

Ahh... so than a broken belt would shut the BMW diesel engine down when the battery runs low.

Lol, I suppose, but you'd have to run it around for a week before you noticed any deteriation, the system only uses small amounts of current to adjust the timing. All the injection energy is taken out of the timing chain onto the main injection pump.

The battery on a diesel model is *massive* - far bigger than the V8 battery - I cant imagine it not giving huge warning signs before it went flat enough to stall the car!

EDIT: By which I meant, it'd be blowing steam from the shut down water pump waaaaaaaaaaaaaaaaaaay before its battery went flat.

[Tiger]

Right... I know... Diesel use group 49 batter... that gives about 1.5 hours of use unless you are using alot of electricity in the car... But definitely that the engine will sieze before battery runs out.

Since it is electronic timing... It needs certain amount of voltage to power... so when it runds down... injection don't work anymore... and also being electronic, it is possible to shut down engine when it reads higher than normal temp. This is best left to those who owns the car and experienced belt loss.

[Ferret]

Right... I know... Diesel use group 49 batter... that gives about 1.5 hours of use unless you are using alot of electricity in the car... But definitely that the engine will sieze before battery runs out.

Since it is electronic timing... It needs certain amount of voltage to power... so when it runds down... injection don't work anymore... and also being electronic, it is possible to shut down engine when it reads higher than normal temp. This is best left to those who owns the car and experienced belt loss.

The injection systems on a car have to cope with a voltage brown out of down to about 9 volts on startup, which is waaaay beyond 100% discharge on a 12V car battery... I was never claiming that battery run off wouldnt stop the car btw.

1.5 hours? That's like a nominal draw of 55+ amps while running - I'm tempted to rig mine upto an ammeter now to find out what it draws during run time. (And my old 525TDs which I still have access to, just for comparison)

[Paul in NZ]

All the injection energy is taken out of the timing chain onto the main injection pump.


Isnt this the key to it...what drives the main injection pump???

[whiskychaser]

Some more info may help decide the issue: The driver states the car started to cut out, he looked down, noticed the high temp gauge and pulled onto the hard shoulder. He left it to cool for a while then removed the rad cap to help stop it boiling up. Then he drove it the rest of the way to work. My estimate is he drove for about 20-25 minutes from cold before the problem, the last 15 being on the motorway. And a further 10-15 minutes to get him to work. So no low battery and no problems with injector pump - which I'm guessing is chain driven anyway - or it just wouldnt run.

My opinion is that the engine was 'picking up' due to overheating. I do think it would be handy if the motor DID cut out to save you wrecking it - rather than giving you a low coolant warning after it seized:(

[Ferret]

Isnt this the key to it...what drives the main injection pump???

The main injection pump is run off the timing chain, wheras the water pump is run off the auxiliary belt... if that makes sense. If the timing chain went, yeah the engine would just stop dead with a loud bang as the physics of an interference engine with no timing chain ran their natural course.

For whatever reason, the system's overheated - and something I've just remembered about my old 205 diesel - if you overheat them they massively lose power due to the combustion going screwy... or something. Heat plays a large part in a diesel engine as there's no traditional spark - just the air charge being hot enough to detonate the directly injected diesel.

I do remember having driven my 205 TD around for a day with no coolant in it, refilled the coolant and it gave me another 2 years of happy service without cooking the HG. Go go peugeot with cast iron block and cast iron head!