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In the bubble wrap insulations, the foil is bonded to the bubble wrap

Actually this is not aluminum foil..it is Mylar. Very different and a much better choice for minimising radiation losses. Wherever aluminum foil contacts the line it will be speeding up heat loss rather than retarding it. Simple and easy but not the best choice..or even close to it. If you check the info on installing reflective "insulation" you will notice that proper installation involves leaving an unbroken air gap between the reflective barrier and whatever it is "insulating".

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The way to check this is of course to get some temperature readings of the injector line's immediate vicinity, while driving,

One might want to also get a reading away from the lines a bit as the temp reading may reflect the heat being lost from the lines otherwise. When I have checked underhood temps in very cold ambient temps I have found it to be much cooler than I thought it would be. One imagines that the heat from the air passing through the radiator and coming off the block would keep it very hot...but this is not the case at road speeds. Perhaps newer engines with tight fitting covers are an exception. But I woudl not assuem this without actually testing to make sure.

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Posted 21 October 2009 03:38 PM Hide Post

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In the bubble wrap insulations, the foil is bonded to the bubble wrap



Actually this is not aluminum foil..it is Mylar.

No, actually, it's nearly pure aluminum in most cases, not Mylar.
That's what gives them their Class A fire rating and their low emissivity.

Mylar is a polyester film...not as good in either respect as pure aluminum.


If using the bubble pack type, it's pretty easy to wrap a line and have an air gap, and any contact points you do have will be insulated (conductive) via the bubble pack (polyethylene)

....and, it's not hard to wrap a line and have an air gap, or more likely a lot of small air gaps (pockets), and a few contact points that will really be of no consequence, even using just plain old heavy duty foil.

Certainly silicone tubing is nicer looking - something pre-sliced along it's length would be nice.

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Originally posted by Edward Beggs:

That is, there is also the possibility of heat *gain* to the injector lines.
Or at least minimal heat *loss*, as the cold air entering the engine bay is balanced out by the heat of the engine itself. It's a bloody hot environment in there in summer, and pretty warm in winter, too, once things are warmed up.

So, the amount of heat lost in the way he's described would be, actually, minimal, I think, with the hood down/hatch closed in a "hot" engine bay, which is when you'll be switched over to SVO.

I agree and put this chilling effect down to the endless Veg paranoia and myths that people like to create in order to sell something or create discussion/ argument.

Under the bonnet of any vehicle is a hot place. Not only is the air from the radiator blowing round under there but you also have exhaust manifolds that can be red hot under load and a great chunk of metal called the block radiating heat as well.
Many cars including the mercs have an air inlet at the front of the Bonnet in order to get cool air into the engine from an area outside the engine bay because hot air knocks off performance and efficiency. Obviously the manufacturers know the air under the bonnet is hotter than the outside air or they wouldn't put the extended inlets on the cars.

I had a vehicle some years ago that I could not stop over heating after doing the engine up with some performance mods. After trying everything suggested to me, one day at home I was looking under the bonnet and drew the mental picture of the heat coming out of the radiator and being sucked straight in again by the engine. I knocked up a crude cold air feed and the engine temp immediately dropped an average 20oC which was a huge margin and more than enough to keep it well away from overheating. I made up a permanent cold air feed using two pieces of insulated foil air con ducting, (one inside the other) and a scoop and never had a moments trouble with the car again.
I must have spent about a grand before I came up with that 10 buck solution which was what fixed the problem.

If one drives their vehicle when it is up to temp for a bit then pops the bonnet and feels the inner guards, under the hood or anywhere else in that area, it will be very warm so I don't give any credit to this injector line chilling theory at all.
In any case, even if the lines were cold, the fuel will soon be warmed up once it hits the injector so what is the problem?

There is a lot of heat being radiated around the engine bay and no matter how cold it is outside, the amount of heat given off by the engine is more than enough to keep things under there toasty.
If the engine itself is running too cold, one might like to make up something to partially block the radiator like the trucks use.

Another alternative if one is convinced that there is still a blizzard under the bonnet would be to make up a windage tray like the racing cars use under the engine bay area to limit the amount of air blowing under there. I have done these before and found thin conveyor belting to be an excellent material for this as it is tough enough to be secured in place with screws or bolts and flexible enough so it can sit on moving steering components without any interference with their operation.
Don't seal up under the engine too well or you will block the flow of air through the radiator. Leave a foot or so open from the firewall and you will only have hot air moving back under the bonnet.

At the end of the day I still think this injector chilling theory is yet just another Veg Myth and The veg world needs to start getting rid of these old wives tales ( of which there are so damn many!)that are meaningless talking points and move forward concentrating on real world problems that actually matter.

I get the feeling that running on veg has been sufficiently explored now to make it reliable enough for everyone and there is little that really needs to be discussed but some want to perpetuate myths so there is something to talk about, a reason to sell accessories and can continue to elevate themselves as veg gods to the inexperienced.

DCS - you just need a dose of Canada to dispel a general lack of understanding that injector lines lose a lot of heat. When it gets to be -40C, that is freakin' cold that you just don't know in Australia, lucky you thinking things are all toasty warm under the hood all the time. C'mon up to where tires can shatter when you hit a hard bump / curb. Forget about plugging in a block heater, I carried a propane blow torch in my old car - to put flame to the oil pan for 20 minutes in hopes to get it to crank over after parking at the airport for a few days.

Go back to your sunshine, while we figure out how to insulate pipes in our igloos.

I monitor the temperature of the #1 injector line where it enters the injector body with a readout on the dash. The injector lines are insulated plus the top 6" and injectors are covered with a battery blanket for pre-warming and as a 'wind shield'. A FPHE between the fuel feed pump and the fuel filter adds heat to the fuel before the IP. The running temperature at the injector line in the winter is 20°C to 30°C less than the summer temperature. So yes, Scott is correct, the ambient temperature does have an effect.

John, at what ambient temp do you see 20-30C lower temps, on your display, as you describe?
(assuming engine fully warmed up)

Ambient temperatures in the -25°C to -35°C range produce injector line temperatures 20°C to 30°C less than the summer maximum of about 80°C at 25°C to 30°C ambient. These are insulated/shielded injector line temperatures at highway speeds of 80-100 kph, not in city traffic. If the injector lines were bare and exposed I would expect the temperature difference to be greater.

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Originally posted by john galt:
... The injector lines are insulated plus the top 6" and injectors are covered with a battery blanket for pre-warming and as a 'wind shield'.

John - you got my ears, injector lines are insulated with what?

And something's not clear, maybe just to me, the top 6" of what... did you do there?

For the coldest days I was thinking of putting a pillow of some sort sandwiched between top of engine and hood, to stop the flow of air going over the injectors, allowing heat up from the block, when it warms. Anybody built an engine cozy?

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Originally posted by Edward Beggs:
..I also had a dealer in frigid Alberta

Hey if you're talking about location in Canmore... I know the one, just converted a buddy's TDI this summer. Only problem is, now he keeps hittin' me up for oil! I suggested he go and get his own centrifuge, so he did. But maybe he doesn't realize you need 2 things to for CF to run well: electricity to spin, and oil at the input.

Thanks for the info, John.

(Scott, that's the one...sounds like you guys need a co-op, maybe?)

I wonder what the flow rate is like on your engine, John? Have you checked? As JohnO says, a low return flow rate would mean a slow flow in the lines, and greater heat loss compared to other engines with higher return-flow.

1 litre per kilometer???

Thanks for catching that, I was in a hurry, it's 10L/100km or 1L/10km

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Originally posted by Scott McPhee:
injector lines are insulated with what?

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And something's not clear, maybe just to me, the top 6" of what... did you do there?

The top ends of the injector lines and the injectors are under the battery blanket

On that engine the fuel feed pump spec is 0.9 L/min [0.24 GPM] at 1000 RPM.
At 2200 RPM, 100 kph, 1.7 km/min, the engine consumes 10L/100km, 0.1 L/km, or 0.2 L/min.
Thus if the fuel feed pump is delivering 2 L/min at 100 kph, 1.8 L/min is returned to the tank.

No worries...figured that's what you meant.

John, that's the split loom wiring harness stuff I have on my back 3 injectors for now, thanks.

Tonight, I found some stuff at Princess Auto surplus called "Thera-Band". It's latex rubber tubing... read about it here: http://www.thera-band.com/stor...ex.php?CategoryID=12
Eyeballing it looked about a good fit, so I bought some. Sure enough is nearly an exact fit. It's inner diameter is stated to be 0.2" and I measured the injector pipes, they are 4.5mm or about 0.178". So I split a section of this rubber tubing by snipping with scissors along its length. And it slips onto injector lines nicely. This material snaps back to its original tube shape quite nicely, giving it good self-closing action around the line.

Don't know if I'll go full force with this idea, because I don't know its insulative qualities, so I'm testing that using a pot of boiling water on the stove. I'm slipping a metal thermometer probe (about the same size as injector line) into an uncut section of tubing, and keeping both ends out of the water, watch the temperature rise rate when immersed into the pot of boiling water.

Not sure what this will show or prove, but maybe I can compare this idea with other materials and repeat the experiment. I figure the slower the temp rise rate observed, the better.

OK, I did it and the result was it took about 4 minutes for the inside of the tube to approach the temperature of the boiling water on the outside, 100C. Then it occurred to me that what matters the most is the cooling off period and not the heating up period. I should compare how long it takes the probe to return to room temp when the apparatus is pulled out of the water and held in open air. And compare that with how long it takes the naked probe to do the same. I could compare different insulative sleeves this way... and in fact just heat the probe to 100C in water, then bring it out and stick that into the sleeve and time the decay. That makes more sense.

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I monitor the temperature of the #1 injector line where it enters the injector body with a readout on the dash. The injector lines are insulated plus the top 6" and injectors are covered with a battery blanket for pre-warming and as a 'wind shield'. A FPHE between the fuel feed pump and the fuel filter adds heat to the fuel before the IP. The running temperature at the injector line in the winter is 20°C to 30°C less than the summer temperature. So yes, Scott is correct, the ambient temperature does have an effect.

John, it sounded from your last post (1.8 litres of 2 litres per minute being returned "to the tank") on this that you are not looping the return, is that correct? And, it looks like you have no electric heat....so, I am thinking that some of the heat loss is simply due to the engine running cooler in winter, and some is due to losses at the fuel tank, if returning to tank (a metal tank under the vehicle, for example is a really good "extra radiator"!. Even a tank inside in very cold temps is going to shed heat to the air around it.

So, if this is the case (no loop, no electric heat), then I am not surprised your temps are lower in winter at the injector, but it does not really tell us that the lower temps are a direct result of losses in the injection lines.

It only tells us, as you have said, that "ambient temperature does have an effect"....basically, that it's really easy to build a system that heats adequately in summer or in warm climates (for liquid oils), but much more challenging to build one that is effective in very cold winter temperatures.

So I think your comment is general, and Scott's original one is specific, and it would still seem that the amount of heat loss at an injector line is going to depend on ambient temperature, flow rate and position and protection of the lines within the engine bay, etc. In your case, flow rate seems to be very high, so perhaps there is not very much loss actually at the injector lines themselves?

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So, if this is the case (no loop, no electric heat), then I am not surprised your temps are lower in winter at the injector, but it does not really tell us that the lower temps are a direct result of losses in the injection lines.

It pretty much does since the coolant temperature and the fuel temperature exiting the FPHE stays about the same. The biggest change in temperature is heat loss between the FPHE and the injectors. If I wanted a higher temperature then I would loop the return. The temperatures I get are fine for the fuel blends I run.

Ok - I guess you'd have to move the temp sensor over to where the lines connect to the pump, and compare with past readings, to be able to tell now how much loss is via the pump versus how much is lost in the lines. I'm assuming you have a distributor rather than inline pump on there.

That engine uses an inline injection pump. Heat loss occurs at the fuel filter, IP, connecting lines and injector lines. The heat loss will be proportional to the relative surface area and the surface area to volume ratio of the different components. The injector lines are a significant contributor. Wind shielding and insulation of fuel system components can increase fuel temperature.

OK, did an experiment with two different kinds of insulative wraps: split loom wire wrap, and this latex rubber tubing I found.

I heated a metal thermometer probe inserted into the material being tested, until 80C was reached.
Then I removed the heat source and let it stand in ambient room temp about 20C and watched the temperature decline in minutes, and charted it. In my mind this sort of simulates heat loss of injector lines wrapped in the material.

First, the latex rubber:
time - observed temp
t=0 - 80C
1m - 66C
2m - 57C
3m - 50C
4m - 44C
5m - 40C
6m - 37C
7m - 34C
8m - 32C

Next, the split loom, like John shows, I think the stuff I used is called size 1/4", as its ID measures about that.
time - observed temp
1m - 41C
2m - 35C
3m - 31C

I have not done the experiment on just a naked probe, for a baseline.

Experiment was done in still air. Put moving air around this and all would drop faster.
Make it colder than 20C ambient, and it would drop faster. But at least it's a good relative comparison that tells me the latex rubber is better than split loom.

So I'm taking off the split loom I put on the back 3 injectors and replacing it with the latex tubing.. Once this tubing has been split length ways, which was quite easy to do, it's really easy to apply if you ran some graphite dry lubricant up the insides of the tube with your finger. Just push it on and watch it snakes itself around bends on the injector lines which is really handy under the manifold where there is little room to reach.

I wish I had some of those cheesy little wire loop spring clamps jobbies to put along in a few judicious places around this tube to keep things pinned down nicely, like on sharp bends to prevent it from opening up.