[SOLVED] fan belt

[harry]

perfect when you buy one year old with 375 miles on the clock.

[The Natural Philosopher]

Not really.

Er no, that is not even WRONG. A 100bhp engine idling at 2 bhp will if its a diesel likely produce 4 bhp of heat and 2 bhp mechanical energy to overcome friction.

If its petrol it will be well off it's efficiency curve and likely produce nearer 20bhp of heat.

At rate output of 100bhp both will likely be producing upwards of 200bhp of heat - 300KW or so.

That is also a factor.

And yet my latest diesel warms up much faster

And is still an iron block/Al head design.

[The Natural Philosopher]

independent will do that for sub 400.

[Dave Plowman (News)]

You don't need to go abroad. The Triumph 1300 series - current with the Mini - was FWD inline engine.

[Dave Plowman (News)]

Don't be silly.

First car I owned with a Sachs temperature controlled viscous coupling, a S1 XJ6 on carbs. Last one, a BMW E39, made until the mid noughties. And they were fitted to later models too. So a life of at least 40 years.

[Dave Plowman (News)]

Fact remains that on comparative sizes, a diesel is generally slower for the heater to get going than a petrol.

[Tim+]

I think we?re generally agreed on that but it?s not solely down to efficiency (although I?ll accept TNP?s point about heat production at idle), it?s largely down to the size of the heat sink and emission control mechanisms that prioritise getting an engine up to working temperature quickly over cabin heating. This is why some diesels have auxiliary diesel fuelled heating systems.

Tim

[The Natural Philosopher]

So as to emit far more CO2....

[Steve Walker]

No. The higher efficiency means that there is less waste heat for a given amount of useful energy produced. Supposedly real world figures are around 80% for petrol and 70% for diesel.

Less waste heat means slower to warm up.

Indeed the extra mass does slow warming, but that is even more of a problem because of the smaller quantity of waste heat being produced.

SteveW

[Dave Plowman (News]

Odd, isn't it? When they first arrived they were little different to a fan belt to change.

Think there's a Ferrari which gets the award, though. Engine out job for a routine cam belt change.

[Dave Plowman (News)]

At full output, the difference in efficiency between petrol and diesel isn't so great.

It's at low output where the two diverge more. Hence things like local delivery vans being diesel for a very long time.

And poorer efficiency means more waste heat. And warming up very rarely happens at full engine output. If it did, most won't last that long.

Of course modern engine management has brought the two closer than once. But hasn't done much about a petrol engines being at its most inefficient when warming up.

[Dave Plowman (News)]

You'll need to explain that. A basic diesel may be slightly more chunky than the equivalent petrol, but not by a big margin.

That's because they take longer to heat up than petrol engines. ;-)

[T i m]

<snip>

Whilst that makes sense on a PC fan to blow the dust out <g>, I don't remember it happening on the viscous coupled fan on my 2L Sierra Estate?

On cold start it may have idled round from the drag in the system but you could very easily hold it when starting and you could only just feel it trying to turn?

Once the heat starts blowing though from the rad however, it really firms up and does it thing.

It sounds like the Volvo one worked differently?

Cheers, T i m

[Tim+]

It just seemed to be ?draggy? when first spun up from cold. Within seconds I guess the oil or whatever inside it would warm and the drag would dramatically drop, at least until the engine was hot enough to actually need cooling down.

I don?t think it was different in principle from any other, it just had a high start up drag.

Tim

[T i m]

<snip>

As was mine but not anything like enough to keep up with the engine RPM, even if given plenty of time (seconds). It did spin up in time (10's of seconds) but still only a percentage of engine revs (because of aerodynamic drag on the fan part of the blade) and if you slowed and stopped it with something (not a finger), you could then still hold it with a finger until you got enough hot water though the rad to heat the bi-metallic actuator on the fan itself.

If like mine it was an aluminium hub (bolted on the front of the water pump) filled with an oil, that was only allowed into the engagement area on the hub when the bi-metallic actuator was hot enough (from air the rad as it wasn't touching anything, other than at the two ends).

?

Maybe the oil would run into the 'drive' position when idle and get moved back into the reservoir after a few seconds of engine revs?

Understood.

Cheers, T i m

[bert]

In article [e-mail]>, Tim Lamb [e-mail]> writes

Just been quoted £475 +vat for cam belt change on VW Transporter by dealer. About to start shopping around independents.

[Steve Walker]

During normal running, the fluid is effectively "pumped" to the hub reservoir and only released when heat opens the valve and lets the fluid out. Once the valve opens, fluid continuously circulates, hub to periphery to hub - and the viscous drag when it is between those positions drives the fan.

It is possible that when stopping the engine, the heat means that valve is open, but the lack of rotation prevents it pumping back to the hub. If so, the fluid will remain between the sections and provide drag on startup, which will only reduce as the fluid gradually ends up back in the reservoir?

SteveW

[Steve Walker]

I was going to change my cam-belt soon (Zafira B 1.8) and was finding kits (including water pump) for around £99. I spoke to a local, independent garage that I trust (I don't trust many of them) and they, because they can buy kits much cheaper, quoted only £150-odd to supply and fit! For the sake of £50-odd, I can't be bothered doing the work myself. I can make that up by spending two extra hours at work.

SteveW

[Dave Plowman (News)]

Some do that. Not sure if all. Seems to take a few seconds before the drive sorts itself out.

But before that cold start, the fan can still be turned easily, engine stopped.

[The Natural Philosopher]

It is crucially dependent on the vehicle.

Some vehicles its a 'cam cover off, lock crank and cam in place, release tensioner, remove and replace belt, replace cover, and go'.

For other vehicles it may mean dismantling half the car to get at it.

It's the same for many other components. On my freelander the thermostat was almost impossible to reach without dismantling large amounts of underbonnet trash, similar for the high pressure fuel pump. But the turbo-to-inlet hose which splits often, is a 2 minute job with a screwdriver.

Clutches that need a complete gearbox removal or and engine removal are another sometimes expensive item