Quote:
Originally Posted by Walkabout
The last few posts have drawn out a few downsides to diesel fuel.

I recall the "good old days" years ago, when the UK winters were generally colder, much colder, and diesel fuel used to cause problems in the fuel tank (turns more viscous I understand, possibly with a separation of the constituents?). Lighting a small(ish) fire under the fuel tank was the answer.

I am prompted to ask: does diesel fuel deteriorate in the tank, in a similar way to petrol, if left over time?

I had not thought about altitude: it's a well recorded issue for carburettored bikes, not so much for Fuel Injection bikes. I thought that all diesel engined vehicles are FI?

It is well recorded that diesel engined road vehicles need regular changes of the timing belt (Ducati motorbikes ditto): this is another downside to the technology IMO because of the additional costs associated with the already expensive fuel here in the UK.
So, do petrol engined 4 wheelers have similar requirements for short-term(ish) servicing?



The good old days of having diesel fuel wax up in most climates have gone with the advent of winter mix fuels, some high tech additives like kerosene usually drop the cloud point of diesel enough for anything except seriously long periods of minus 15C and below. Most truck manufacturers selling into known cold markets will include "Arctic/Alaska/Siberia kits" of fuel tank heaters and insulated and 24V traced fuel delivery lines as well.

Diesel will deteriorate over time, but usually its an algae that grows in the tank, an additive will stop that. Its more likely that condensation inside the tank will cause problems over time. The fuel will float on the water, the pump will pick up water and the owner claims bad fuel, always a good idea to have a water separator before the fuel filters which can be drained off. Most diesels have some sort of manual lift pump, so its a good idea to use that if the vehicle has been sitting for a long time, you can get the water into the separtor, drain off, then fire up the engine. Once the water is in the filters and pump its time to start replacing bits.

With altitude problems, its a fine line between the reduction in oxygen and reduced temperatures which then reduces the burn of the diesel fuel - the same problem occurs on petrol engines as well but its not as critical as there is a spark plug to cause ignition. Whereas diesel requires the compression and heating of the air charge then the injection of the fuel into the hot air to cause the burn. My memory fails me a bit, but I think the optimum temperature to oxygen density of the air charge is 38C, hence the need for cooling the air charge down with intercoolers and aftercoolers on turbo engines. There are so many brands of "cold start" aerosols on the market its not funny, all have an ether and butane base, couple of squirts into the air cleaner and any diesel will start as long as there is fuel.

Modern electronic diesels also have oxygen and temperature sensors which can accomodate altitude (low oxygen) and temperature differences by retarding or reducing fuel injection times. Overfueling a low oxygen air charge will not let the fuel burn as the mix will be "too rich" in old terms. But when the circuit board dies in the middle of Whoop Whoop unless there is a "limp home" mode you are stuck.

I've not heard specifically of timing belt problems for small car diesels, in commercial based vehicles it would be a brave engineer who specified changing timing belts/chains at less than 500,000kms on a light truck, and up around the million kms on a heavy truck.

Servicing of diesels based on Kms is really a hangover from the pre electronic days, the engine and driveline should be serviced based on engine revolutions which is an indication of the work done. Best aftermarket purchase you can make is a total engine revolution counter. I've seen metropolitan delivery trucks rack up the same amount of engine revolutions with stop start driving in 8 weeks as a highway truck does in 14 weeks.

With regard to diesel deteriorating over time then yes, as Roger says algae can be a problem as can the accumulation of asphaltenes as the diesel breaks down - this is a black/brown sludge which quickly blocks filters, and will accumulate in tanks over time. It will not wear out pumps but it will cause problems...

Timing belts: well the Landrover Tdi300 engine was quite renowned for snapping in early versions and causing obviously major problems! Toyota allegedly not but I have seen at least one case of an (admitedly) abused 1HZ giving out while still within service interval (which is 150,000 kms on a 105 cruiser IIRC). Most Nissans I have used (TD42 Patrols and 3.2 litre D22 p/ups) seem to have nicely stuck with chains... Which landrover went back to for the TD5 but I have no idea what their new engine is!

My only other contribution is that CAT offer an ether injection system for starting big diesels in cold climates!
hope it helps a little bit,
Gil

For me the main advantage of a diesel engine is that it will have much more torque than a petrol fueled one.

I have run my petrol 4x4 (1986) for over 100,000miles now ( 170,000 on the clock) and have been completely happy with it. It has an engine model with which I am very familiar having done over 500,000miles in 3 vehicles -
it uses slightly more fuel than the equivalent deisel
it cruises at 10mph higher than the equivalent diesel and about the same as a TD5
service intervals are 6000miles but could stretch to 10,000
wading depth is around 900mm and I have never had a problem with damp starting
the injection system is no more prone to failure than a modern diesel
the ecu is a tried and tested (24years) design
I carry a spare ecu, fuel pump and metering head.(mercedes parts are easily available in just about every country in the world)
Absolutely no complaints except lack of low down torque and for that reason alone I am going to swap in a diesel which, sadly will have an ecu, (all be it a 10 year old proven design). the good thing is over double the torque with the same bhp

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Chris
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"Never have a stupid argument with an idiot - he gets a lot more practice than you"
there I go again
not too hard really

I just want to record my thanks for the discussion of petrol Vs diesel fuel.

Inevitably, the points made could not completely ignore particular aspects of the engines themselves, the design of engines or particular makes and models of 4 wheelers.
There is at least one other related thread in the 4Wheel overland travel forum - it is specifically about travelling in the Stans (but I could not get a link to work!). Interestingly, the apparent decision there is to go with a petrol engined vehicle (4x4 fiat panda) in preference to the equivalent vehicle with a diesel engine fitted, especially on the grounds of initial capital cost and the complexity of modern generation diesel engines.

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Dave

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