Hi,

Neo_VR responded to a different thread here and referred to fuel temperatures in it. Just to expand a little - to get the best performance as well as keeping the engine happy the amount of fuel injected is tweaked based on (amongst many other things) fuel temperature.

The return line on the vRS has a fuel cooler in it. Since that time I've spotted a thread on SCN here

As I have a FMIC already, my SMIC has been removed from the usual location. From the pics on SCN it looks like the fuel filter is quite easily accessible from there.

Some questions then:

1. Anyone here tried that kinda thing? I spotted Mr Jason when Googling.

2. If you have any links to actually measured temperatures with such a thing fitted that would be excellent

3. As the Forge FMIC runs it's pipes through the SMIC area there is limited space BUT I reckon a small intercooler should fit (custom bracket would be needed though). Alternative is to stick a second 'OEM' fuel cooler into the return line assuming there is space under the car to do so.

Similarly I'm wondering about oil temperatures on highly tuned PDs. Jason's is more highly tuned then mine but the one thing in common which could increase the amount of derv returned would be the propane injection?

Just some random thoughts at the moment but as I'm aiming to keep temperature loads on the engine in check, it's just something I'm considering

Looks interesting, and has been sufficient for me to get my mate on the lookout for an old heater matrix sometime. Its probably only a marginal difference though. I can never install one in that position, but it's nice to see a guide for it.

Correct me if I'm wrong here but isn't the reason that colder fuel gives better performance is because it's denser when cold & therefore there's more of it ?

Is that not why the fuel temperature is monitored and adjusted by the ECU to supply a little more when it's warmer to keep performance up ? This is also how the "evry mod" works by tricking the system into thinking the fuel is actually warmer than it is & the engine management system then supplying more fuel ?

That being the case (and I'm maybe way off line here) how would cooling the fuel via a FMIC type device or whatever help if it's already being compensated for by the ECU ?

Edited to add: Ok, just read the SCN link and I understand what's being said now, very marginal gains methinks.

@Jason

Same here, I reckon the diff won't be a lot but at the same time if the fuel temperature is right the fuel economy will be better too from what I can gather

Same prob as you having fitted the FMIC where the guide suggests fitting it

@TD-eye

spotted your post just after I responded again myself

Basically as you say, it will compensate by sticking in more fuel. This means more fuel is used. Beyond driving more sensibly/slowly to save (quite substantial amounts of) fuel, if this increases fuel economy during hot days by a couple of mpg it will be worth it for me VERY quickly as I do lots of miles. Cost of this kinda thing would be around 200 quid tops I'd have said.

Same prob as you having fitted the FMIC where the guide suggests fitting it

But I have a good bit of turbo pipework I could attach a cooler to, right down by the offside front panel. And that panel vents nicely too.

All things to consider, but its not on my to do list at the moment - Just a "as an when" mod.

Ditto - that said I'm gaining interest in it

Honestly, I think that would make next to no difference.

Anyhow, if that doesn't have a good flow of cold air going to it, it would probably warm the fuel up rather than cool it down.

Fleabay has some interesting stuff on it. Could be a bit of fun.

most the parts are readily available on fleabay... whole mod cost is less than 50squid, and its very effective

Looks to me that rather than using a fuel cooler, you can use a heater matrix and adapt that to circulate fuel, as opposed to water. Also a heater matrix looks nice and easy to get down in the airflow as its shaped much like a SMIC. Just with smaller pipes coming off each end.

Right, can a techie now teach the unitiated about the benefits of cooler fuel please? i.e totally in full, nothing abbreviated.

I suppose it's a bit of fun trying to squeeze every last bit of bhp out of your motor.

However, if you take "Basils" maths as being correct in the other thread and accept expansion of fluids works equally as well in reverse ie. gets denser as it cools then your cooler is going to have to drop the fuel temperature by quite a considerable number of degrees to gain any useful extra fuel over and above what is already compensated for by the ECU & therefore more horsepower.

That said, I'd be very interested to see any before & after rolling road figures not that I'd go down this route you understand ... just curious!

Have fun guys !

Well basically diesel is quite succeptable to changes in temperature changing the density.

the ECU is suppost to compensate for this by injecting more fuel..(also how resistor mods work)

but it isnt ideal... and belive me the fuel gets effing hot.. regardless how you drive, because the fuel rail pressure is always the same theres a constant circular flow of fuel between the tank and engine, the less fuel you have in the tank.. the quicker the temps will rise... and just like intake temp.. the engine will start to wind off the boost and power around the 85-90c mark.

So over time, even on a full tank the temps will rise, and the fuel will expand.. which is why we have the 2 gallon expansion tanks. its why the car will suddenly feel a bit sluggish/smokey after a bit of a run..

ill nip out for a quick up/down dual carridgeway and get some vagcom logs.

these will be without the fuelcooler as i had to take mine out because it was leaking

Thanks Colin

As for the bhp increase(s) - much like the FMIC, there won't be any, but it may be able to sustain maximum bhp possible for longer.

Thanks Colin

As for the bhp increase(s) - much like the FMIC' date=' there won't be any, but it may be able to sustain maximum bhp possible for longer.[/quote']

Well im back..

didnt get a decent run (only managed a max of 5 seconds a time on WOT)

ambient was 19c

had qtr of a tank of fuel. which was 18c when i started the car

in the 10 miles over 15 minutes the fuel temp hit 73c. it was too busy to push the car hard... was stuck at light throttle at 70mph for most of it... oh, highest intake temp was about 45c.. only a slight rise over cruising once engine was warm

Well im back..

didnt get a decent run (only managed a max of 5 seconds a time on WOT)

ambient was 19c

had qtr of a tank of fuel. which was 18c when i started the car

in the 10 miles over 15 minutes the fuel temp hit 73c. it was too busy to push the car hard... was stuck at light throttle at 70mph for most of it... oh' date=' highest intake temp was about 45c.. only a slight rise over cruising once engine was warm [/quote']

So over a period of 15 minutes you managed to raise the temperature of a quarter of a tank of fuel ( say 3 gallons ish ?) by 55 degrees ..... that's more than I expected !

Heres the graph...

bit of a mess coz i cant use excel for toffee

time across the bottom in seconds... temp on left

Fuel temp is in red, intake temp is in green (you can see from the spikes where id booted it) and coolent is blue - first couple of mins is me on local roads going to the dual carrigeway. same at the last few mins.. is mostly down hill so no throttle

incedently.. because ambient temp was 19c.. anything above that, i usually definately notice a big drop in performance.. so its borderline. also in the same logging group on vagcom theres a reading "fuel cooling state" which can either be on or off... dont know what this is, maybe activates when it hits 90c?

if anyone wants the raw data to do a better job.. gimme a shout.

It's quite interesting to see the fuel temperatures go up that much in such a short time :eek:

Thanks for the info so far and I will try to get some more info on this in the nearish future (funds permitting, still awaiting feedback on the maxidot which could be very expensive )

Neo VR ,where is the temp reading taken from ? is it a sensor somewhere in the fuel system ,is the sensor before the injectors or after in the return line ? i wouldn't think there was a sensor in the tank reading the fuel temp in there (could be wrong) so if the readings taken were in the return and before the cooler the tank reading would be lower ? or is it somewhere before the injectors therefore reading the temp of the fuel from the tank , please correct me if i'm wrong i'm trying to get my head round what your trying to do . also i dont think its a good idea to have the fuel overcooled on a cold winters day

There is a sensor in the fuel line after the pump IIRC.

Quite right on overcooling, not a great plan. That said there is a valve in the system that prevents that apparently

Their a thread over on Tdiclub about this http://forums.tdiclub.com/showthread.php?t=142861&highlight=fuel+cooler

Thanks for the link reading up

There is a sensor in the fuel line after the pump IIRC.

Quite right on overcooling' date=' not a great plan. That said there is a valve in the system that prevents that apparently [/quote']

IIRC its on the right hand side front of the engine, just before the fuel enters the high-pressure pump on the side of the camshaft

IIRC its on the right hand side front of the engine, just before the fuel enters the high-pressure pump on the side of the camshaft

So there's no pumps between the fuel rails and the fuel tank then? I thought there may have been one on the tank? As long as there's effectively nothing but the filter between the tank and the engine, there's lots of scope for fiddling (and I have 5m of high grade fuel pipe left over from my lpg install )

So there's no pumps between the fuel rails and the fuel tank then? I thought there may have been one on the tank? As long as there's effectively nothing but the filter between the tank and the engine, there's lots of scope for fiddling (and I have 5m of high grade fuel pipe left over from my lpg install )

Theres also a electric-pump in the fuel tank...

Theres also a electric-pump in the fuel tank...

Had my front bumper off earlier today (don't ask) - Loadsa room for a cooler and loadsa room to get fuel pipework down/up from the filter area too.