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Old 11th September 2012, 20:35   #121
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

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Originally Posted by Aroy View Post
sufficient to play havoc if the wax clogs up narrow passages.
Any form of precipitate chokes the filters. These filters are on the suction side, so you really can't force fuel through them.

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Sutripta
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Old 11th September 2012, 21:25   #122
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

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Ooty is not really high altitude in terms of location but for what it is worth, my Yeti started first crank the other day after sitting out in the cold all night. It was switched off and outside from 930pm to 9am. The temperature that night was about 7 degrees at its lowest ebb. Anyway it was cold enough to warrant a roaring fire in our room.
I don't think that a car designed for European cold temperatures will have any trouble handling our scenarios here, except maybe in the depths of winter in the Himalayas somewhere.
Neither ooty can be called cold
Night temp drops to 0 and -1 in plains in north at many places and summer peak temp is above 45 at same location
Few examples which I can recall are Pathankot Sri ganganagar adampur kota Amritsar Gwalior etc.
There is no start trouble for modern diesels there except for old Amby with shot glow plugs and weak battery.
Sorry for punctuations typing in a mobile browser.
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Old 12th September 2012, 10:13   #123
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

All High altitude areas get Winter grade Diesel, which is a blend of regular Diesel with ATF/ Kerosene cut. During winters all of North, Central, North east get winter grade Diesel, with a Maximum pour point of 3 C. However actual pour point is in the range of -6 to -15 C. The cloud point spec for such fuel, when the dissolved wax starts crystallizing is max 6C, actually it may be around 0 to -6C. Fuel generally should not be a problem. Most fuel lines are nylon and tanks are fibre, which is sufficient insulation to keep the fuel well above cloud and pour points.

With little application of glow plugs and few cranks most cars should start.

For Extreme cold weathers where only Military vehicles are plying they get a special grade of diesel which is mostly ATF. Also Russian Military & US Army run exclusively on JP5, which is also an aviation fuel and a Kerosene cut.

If your car is not starting in in cold weather upto -15C then the problem may be mechanical rather than with fuel. Some Fuel lines may be poorly designed with sharp bends which tend to accumulate wax. Exposed metal lines are more prone to waxing and clogging.

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Old 13th September 2012, 15:29   #124
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

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Originally Posted by Sutripta View Post
Any form of precipitate chokes the filters. These filters are on the suction side, so you really can't force fuel through them.

Regards
Sutripta
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Originally Posted by SR71A View Post
All High altitude areas get Winter grade Diesel, which is a blend of regular Diesel with ATF/ Kerosene cut. During winters all of North, Central, North east get winter grade Diesel, with a Maximum pour point of 3 C. However actual pour point is in the range of -6 to -15 C. The cloud point spec for such fuel, when the dissolved wax starts crystallizing is max 6C, actually it may be around 0 to -6C. Fuel generally should not be a problem. Most fuel lines are nylon and tanks are fibre, which is sufficient insulation to keep the fuel well above cloud and pour points.

With little application of glow plugs and few cranks most cars should start.

For Extreme cold weathers where only Military vehicles are plying they get a special grade of diesel which is mostly ATF. Also Russian Military & US Army run exclusively on JP5, which is also an aviation fuel and a Kerosene cut.

If your car is not starting in in cold weather upto -15C then the problem may be mechanical rather than with fuel. Some Fuel lines may be poorly designed with sharp bends which tend to accumulate wax. Exposed metal lines are more prone to waxing and clogging.

Regards.
I think that SR71A has a point - badly designed fuel lines will accumulate waxes
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Old 13th September 2012, 19:37   #125
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

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I think that SR71A has a point - badly designed fuel lines will accumulate waxes
You mean something like atherosclerosis in the human circulatory system? Wouldn't this clog fuel supply even when the engine is at running temperature?
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Old 13th September 2012, 19:55   #126
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

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You mean something like atherosclerosis in the human circulatory system? Wouldn't this clog fuel supply even when the engine is at running temperature?
When the engine is running, the fuel keeps circulating in a closed loop under pressure, so small amounts of wax will just be pushed out; and even dissolve; as the flowing fuel would heat up marginally initially and quite a bit after some time. In case the car runs rough for the first few minutes, this corroborates the hypothesis.

When the car is stationary, the wax may just about constrict the passage, so less fuel will be going in.

Again as this happens only at high altitudes, coupled with the fact that it does not occur when anti gel is used, wax precipitating at low atmospheric pressure seems, to me, a plausible reasoning. To verify if this the correct diagnosis, carry the antigel, see if there is a starting problem in the morning, add the anti gel after the car starts and then test it next day. If no problem then it is gelling, else we are back to square one
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Old 13th September 2012, 20:06   #127
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

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...small amounts of wax will just be pushed out; and even dissolve...
When the car is stationary, the wax may just about constrict the passage, so less fuel will be going in.
With a stationary car (engine off), at any particular point in the fuel line, one can only expect 1-2 ml of fuel to remain. How much of wax will it deposit out, to clog the line during cold start? As to the fuel gelling in the whole fuel line, I would think that is a different issue altogether, and gelling will happen irrespective of the design of the fuel lines - and an antigel will sort out the matter.

It is not as if a fuel line with lots of sharp bends will promote higher gelling of the fuel as a whole - IMO the bends may promote deposition of wax "plaques", constricting the flow, in which case operating the engine at any temperature at all will starve it of fuel.
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Old 13th September 2012, 20:56   #128
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

^^^
I think we should start another thread on starting diesels when cold. Because I think the focus of this thread was to be CRDIs and high altitudes.

Regarding choking, it is like a chain. The weakest link will be the first to fail. IMO, it will be the filter.

The orifice in a CRDI injector are incredibly small. The pipes/ rail cross sectional area is 1000s of times larger.

Regards
Sutripta

PS: SS- are you thinking of stents and bypasses now?
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Old 13th September 2012, 20:59   #129
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

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PS: SS- are you thinking of stents and bypasses now?
No, just balloon angioplasty!
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Old 14th September 2012, 11:36   #130
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

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With a stationary car (engine off), at any particular point in the fuel line, one can only expect 1-2 ml of fuel to remain. How much of wax will it deposit out, to clog the line during cold start? As to the fuel gelling in the whole fuel line, I would think that is a different issue altogether, and gelling will happen irrespective of the design of the fuel lines - and an antigel will sort out the matter.

It is not as if a fuel line with lots of sharp bends will promote higher gelling of the fuel as a whole - IMO the bends may promote deposition of wax "plaques", constricting the flow, in which case operating the engine at any temperature at all will starve it of fuel.
Gelling beyond pour point, when the fuel will not flow freely will happen across the fuel system regardless of design. The design becomes important at temperature range between Cloud Point (when wax starts to crystallise) and Pour Point (When Fuel stops flowing, though still not completely solid)

A sharp bend will create a trap for the wax crystals when the fuel temperature is below cloud point but above pour point. Whereas a straighter line will allow the fuel to flow relatively freely even if slightly waxed. Above cloud point fuel is completely liquid and will not deposit any wax. As fuel warms up due to warmer fuel returning via return line, the clouding will reduce and thereby the clogging.

Once the fuel reaches below Pour point only external heating works.

Most people who travel to High altitude areas carry substantial quantity of plains Diesel in their tanks, which clouds at much higher temperatures.

Since most car engines these days are CRDI, it can safely be assumed that we are talking about majority of Diesel cars.

Additive added to fuel before going to cold areas should work. Adding them to fuel tank after the fuel Clouds over may not be of much use.

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Old 14th September 2012, 16:20   #131
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

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........

A sharp bend will create a trap for the wax crystals when the fuel temperature is below cloud point but above pour point. Whereas a straighter line will allow the fuel to flow relatively freely even if slightly waxed. Above cloud point fuel is completely liquid and will not deposit any wax. As fuel warms up due to warmer fuel returning via return line, the clouding will reduce and thereby the clogging.

.........
You have put; what I wanted to say; succinctly.

In past, have seen drivers of diesel Ambassadors, lighting fire under the sump before they start the car in the morning, after a heavy snow fall. So cold (resulting in highly viscous fuel) did affect non CRDI cars also.
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Old 15th September 2012, 04:09   #132
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

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You have put; what I wanted to say; succinctly.

In past, have seen drivers of diesel Ambassadors, lighting fire under the sump before they start the car in the morning, after a heavy snow fall. So cold (resulting in highly viscous fuel) did affect non CRDI cars also.

Tangential to the above - how badly does cold affect lubricants?
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Old 15th September 2012, 14:58   #133
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

@ Vina. Engine oil also undergoes similar gelling and freezing process in cold. Suitability of engine oil for a particular ambient temperature range can easily be sourced from the internet.

If the oil freezes the engine may still start but the oil will not circulate as the pump will not be able to push it to all the nooks and crannies resulting in engine failure.

Most common grades ambient temperature ratings are given below.

20W40 is suitable from -6.7 to 40C
10W40 from -17.8 to 40C
5W40 From -29 to 40C

Regards.
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Old 15th September 2012, 19:37   #134
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

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Tangential to the above - how badly does cold affect lubricants?
Cold affects all fluids. It just depends on their freezing point. Heavy oil thicken faster, unless viscosity modifier is used. So you may have a situation where the engine oil has become extremely viscous and the gear oil has jammed the GB, not to talk of the differential which has a more viscous formulation.

Fuels also freeze, diesel much before petrol. When they heated the Ambassador's sump, they were heating fuel pump also.
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Old 15th September 2012, 20:55   #135
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Default Re: Common Rail : Why is cold start tougher at higher altitudes

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Originally Posted by SR71A View Post
...

Most common grades ambient temperature ratings are given below.

20W40 is suitable from -6.7 to 40C
10W40 from -17.8 to 40C
5W40 From -29 to 40C

Regards.

Thanks SR71 and Aroy, I do understand that all fluids will eventually freeze at low temp. but was not aware of whether engine oil can be a problem too (apart from diesel itself)
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