Fuel Cooler...

FlyTDI Guy

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Nov 3, 2001
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PNW
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'01 Jetta GLS
I'd like to see some data on how rapidly the rise in temperatures in the fuel tank, where hot fuel returning from the engine is mixed with fuel at ambient temperature.
Also, how effective is a fuel cooler going to be if the air blowing through the cooler is 100°F or 130°F or 160°F? The hotter the day and the hotter the "track" temperature, the less effective the fuel cooler will be.
This is true... I now have a new/different car, same 11mm but sans fuel cooler (for now). I witnessed some pretty alarming temps last summer, both fuel and intake. Didn't log anything and I don't really remember the exact numbers. I do remember being pretty surprised though.

I would tend to agree with everything above, intake temps are probably more of a concern for me right now. During hot days, the engine bay is easily 160º-180ºF and the intake air, even hotter. It's a bigger IC for me right now. In terms of performance, I would say there's more to be gained there.

I will install the fuel cooler. I still feel it's good insurance. My only reservation would be cold climates. It's pretty hot here right not, maybe I'll log something tomorrow...
 

nicklockard

Torque Dorque
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Aug 15, 2004
Location
Arizona
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2010 Touareg Tdi w/factory Tow PCKG
TornadoRed, you're spreading a lot of partially informed knowledge around of not much benefit, especially in the 3rd and 4th paragraphs of post 87.

TR said:
Aditionally, if the fuel temperatures are already ~110° when you start your trip, you would have to travel several hours before the fuel temp would climb much higher. The best you can hope for with a fuel cooler would be to keep the fuel from getting much hotter than 110°. But the air temps would affect performance no matter how far or how long you drive. And the air temps would limit the effectiveness of a fuel cooler, too.

Thus, it would seem to me that a fuel cooler can have only limited effectiveness, even in the most extreme conditions. And even less effectiveness in more temperate climate zones. The only exception would be if you plan to drive several hours at a stretch, during which time the hot fuel being returned to the tank could raise the temperatures there by many degrees.
There's so much confounded anti-logic here, it's hard to know where to stab this dragon of goofiness.

TR said:
Aditionally, if the fuel temperatures are already ~110° when you start your trip, you would have to travel several hours before the fuel temp would climb much higher.
No, the hotter the ambient temps are to begin with, the faster your fuel will heat up, and it will sustain higher steady-state temps as well.

TR said:
The best you can hope for with a fuel cooler would be to keep the fuel from getting much hotter than 110°.
Yup, but so what. That's a BENEFIT, duh. Your intercooler suffers from the same thermodynamic limitation, but I don't see you poo-pooing intercoolers.


TR said:
But the air temps would affect performance no matter how far or how long you drive. And the air temps would limit the effectiveness of a fuel cooler, too.

Thus, it would seem to me that a fuel cooler can have only limited effectiveness, even in the most extreme conditions.
This is the first part that's made any sense at all. But you're just stating the obvious, that hot air is hot. If you changed the word "even" above to "especially" then it would ring more true.

TR said:
And even less effectiveness in more temperate climate zones.
Wrong. It's much more effective in temperate climates, because of the temperature differences you hinted at before. Have you been drinking?

TR said:
The only exception would be if you plan to drive several hours at a stretch, during which time the hot fuel being returned to the tank could raise the temperatures there by many degrees.
__________________


Fuel temperatures do matter, as do IAT's. And you're making wild inferences about asphalt temps heating air approaching 160f? Where do you get this stuff from? Have you ever recorded intake air temps that high? I really doubt it. Show me the numbers.

I recorded some data on a dynometer with my old 2002 Tdi



You can estimate a linear rate of temperature rise of 3 degrees celcius per minute--look at the plots. Fuel temperatures obviously rise rapidly under even mild load, and we were just testing it on the dynometer at 60 mph, constant speeds! Your last inferred claim that fuel does not raise in temps much or very fast is dead wrong.

I've logged fuel temps of 73C (My Tdi did not have fuel cooler). That's hot. Real hot. Too hot to touch.

You can see that as fuel temps rose in each run, fuel consumption dropped in a pretty strongly related inverse correlation--Ernie Rogers has discussed the physics behind it here in other threads before.

But another thing to strongly consider is that hotter fuel has worse lubrication properties, and since fuel system components depend heavily on that, you don't want to compromise it, so fuel cooling does matter.

Opinions are great. But qualified ones are even better.
 
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TornadoRed

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2003 Golf GL 5-spd, red; 2003 Golf GLS 5-spd, indigo blue; 2003 Jetta TDI wagon, Candy White
Nick, I have been drinking and that probably explains why I do not fully understand your reasoning. For example, you report a 3° Celsius increase in fuel temperature -- where is this measured? Is this fuel returning to the tank, is this fuel IN the tank, is this fuel flowing from the tank?

You state: "the hotter the ambient temps are to begin with, the faster your fuel will heat up, and it will sustain higher steady-state temps as well. "

Maybe... but ambient air is already hot, how effective can a fuel cooler really be?

You ask: "It's much more effective in temperate climates, because of the temperature differences you hinted at before. Have you been drinking?"

Yes, I think I already made that clear, I have been drinking. You might be making a good point, I can't tell. Are you saying a fuel cooler works better when ambient air temps are low? If so then you are probably right -- but it might also mean that a fuel cooler is not needed as much in a temperate climate. Does that make sense? You need something to cool down the fuel in a really hot zone, but a fuel cooler can't do the job. It can only be effective in a temperate zone, where it's not needed as much.

You state: "you're making wild inferences about asphalt temps heating air approaching 160f? Where do you get this stuff from? Have you ever recorded intake air temps that high? I really doubt it. Show me the numbers."

No, I have not recorded intake air temps that high. But surely you've heard of road temps hot enough to fry an egg? How hot is that? I've been on asphalt roads where it was hot enough to melt the asphalt. How hot is that?
 

drejck

Well-known member
Joined
Jan 17, 2010
Location
slovenija EU
TDI
golf3 1,9tdi 81kw
after all this reading its a little mess,where do i install fuel cooler befor ip or after?
or i have an option to install whole fuel cooling sistem from vw pd atj or ajm.
it is a air,water and electric pump based,with something like a little cooler on fuel filter.
 

Houpty GT

Veteran Member
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South Carolina
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Corrado TDI, 2000 Golf, 1996 B4 Variant
I like this thread. I have a few questions I have not found the answer to though!

At what fuel temp does it start to cut power?

Are tuned cars the same or have they changed the programming for this?
 

mrflashy

Veteran Member
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May 29, 2009
Location
UK
TDI
Stage 2 Hybrid TDi and a couple of 24v VR6's for the noise
could somebody point me in the right direction on which side of the thermal T we connect this and which pipe is the return i need to join to the outlet of the cooler.

I would like to know more on the ECUs effects of high fuel temps, did a log on mine on a 30oC day, PD130 ASZ, Hybrid turbo, ~240bhp with a big FMIC and Water Meth Injection cooling intake temps,

My ambient fuel temp was 44oC with a cold engine (well it has been sitting in the sun all day), once i had finished a 15 mile journey some of which on highway my fuel temp was climbing continually regardless of my speed, and at 82.9oC it reached peak and i struggled to get it down again regardless of what speed i did on the highway. During this time by intake temps never went above 40oC due to the size of my intercooler and water meth injection.

That is on a pd130 ASZ engine with the OEM fuel cooler

I can feel the car slowing in the heat and slowing the build up of boost considerably different to that of a fresh morning, and i know its not intake temps causing it
 
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robnitro

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NYC area, NY
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2001 Jetta TDI GLS silver
I can feel the car slowing in the heat and slowing the build up of boost considerably different to that of a fresh morning, and i know its not intake temps causing it
That's because the ECU compensates too much for fuel temp, by pulling back timing. I believe it was for emissions, to cut back NOx as hotter fuel causes a hotter burn and slightly advances it.

I doubt that the density of the fuel is that much of a big deal.. From a table I found, from 15C to 65C, there is a 3% reduction in density.

You can also mod the fuel temp sensor to never read above a number, I used 30C. I can't seem to find the thread right now, it's called kerma kfc mod or fat mod.
 

TDikook

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Biloxi, Ms
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'06 Golf Anthracite Blue
as I stated a few years ago, save your money. I did 2 fuel coolers, didn't make a difference. not worth the effort. do an oil cooler if you run it hard, if not. look elsewhere to mod your car.
 

TornadoRed

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2003 Golf GL 5-spd, red; 2003 Golf GLS 5-spd, indigo blue; 2003 Jetta TDI wagon, Candy White
TDIKook and robnitro may both be right. Tricking the ECM into thinking the fuel is cold may work better than actually trying to keep the fuel cool. Every summer I think about doing that mod, and every summer I put it off. But I observe the same symptoms -- poor performance and sub-par fuel economy when the fuel is hot. I've even been topping up the tank more frequently, to see if that makes a difference, but so far I'm not seeing any change in fuel economy
 

FlyTDI Guy

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'01 Jetta GLS
As I stated before, I never observed anything overt when running my uber-large fuel cooler.

Some observations though...
a) I wondered how or if it was working against me when it was freezing out.
b) It definitely brought temps down in the summer.
c) Ultimately, it effects timing as hot fuel is that much closer to combustion point so... less advance.
d) It's stock equip. for the 11mm so VW must have thought it a valid inclusion.
e) If I run another one, it'll be smaller (I have both a 2 and 4 pass, smaller than the 6 pass I ran before).
f) If I'm going to take up front radiator space, it'll be an IC this time.
g) It you track or tow frequently, more likely to do some good.
h) If I lived in Death Valley, Texas or Arizona, might be more relevant.

So that's it... is it a worthwhile mod? In my climate and considering my driving habits, ehhh.
 

TDikook

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'06 Golf Anthracite Blue
with an ALH, or Injection pump Diesel, I would agree, but with the PD engines, total waste of time.
 

robnitro

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Location
NYC area, NY
TDI
2001 Jetta TDI GLS silver
I run a cooler because my fuel loop is a bit different... I have my return restricted - so some of the fuel returns to the filter (and pump). Doing that makes the fuel much hotter without a cooler.

I did the fuel temp mod a while back before I had this setup, because I didn't like the idea of timing getting pulled back.. more smoke, less efficiency, higher egt.

c) Ultimately, it effects timing as hot fuel is that much closer to combustion point so... less advance.
Yeah it does effect timing but I doubt that fuel at 30c vs fuel at 90c will change timing that much when cylinder temps are MUCH higher from compression. Also how much heat the fuel gets from sitting inside the injector near the hot head???

Same goes for the timing map n108- why atdc for low loads, and an island of BTDC (bumps like hills on map) for certain ranges? NOx and then the bumps for fuel economy testing is theorized.

d) It's stock equip. for the 11mm so VW must have thought it a valid inclusion.
Probably to cut back NOx without having to cut timing?? Also they are running some tiny nozzles on that 11mm pump, which must make it work harder than normal or bigger nozzles.
 
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KERMA

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here
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99 beetle and 04 jetta
knowledge has advanced over the intervening 10 years since my first post on this subject (in the other thread)

COntrary to what was formerly presumed, fuel temp is not an input to timing. Inputs include IAT, CTS, Baro. CTS affects fuel temperature in the physical world in a PD because the fuel runs through the head but not because of ecu programming unless you unplug the CTS

Fuel temp affects duration of injection, however. ECU compensates for lower fuel density at higher temps by increasing the duration for example. This is how the cheap ebay "chips" work (albeit in a limted way). It's why many "tuned" cars tend to smoke more in the summertime, and tend to feel like they make less power in summer also because of the way they are <clears throat> tuned. The factory calibrates ecus so the car performs more consistently over a wide range of environmental condtions, and implementing fuel temp compensation is one of the several provisions for accomplishing this.

Believe it or not, there also is a provision present (present but inactive in most implementations ;) including the factory one) for the lower energy density of biodiesel...
 

mrflashy

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Stage 2 Hybrid TDi and a couple of 24v VR6's for the noise
Thanks guys, Glad i bumped this one backup, so what we are saying, is i cannot avoid the slowness in heat unless i trick the engine into thinking its cooler.

As i believe i am on the limits of the injectors already, and i know i'm doing well to get 240ish bhp from a pd130 in the first place.

Would anything else help me at this time of year to retain some of the extra torque i seem to be loosing? surely oil temperature isnt going to be the likely culprit of my slowness on a 15 mile journey?

I do have black smoke on my map on WOT, and always have, but i am not getting full power in this heat compared to cooler evening driving/early mornings.

Do i now aim my thoughts at MAF readings, i barely touched the 1249 MAF limit on a run last night, running an OEM Airbox with larger snorkel and a green panel filter.
Or could it be the flow of the intercooler pipework? still running the pancake pipe in the wheel arch! :)
 
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TDikook

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'06 Golf Anthracite Blue
Intercooler. these cars do not like the heat!! I did a drive from the Gulf coast to Milwaukee, and I could tell the difference of how the car ran from one point to the last. cooler drier temperatures, these cars Love that. temps go up, they resist. you might not be able to do anything but wait till fall and winter...
 

robnitro

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Location
NYC area, NY
TDI
2001 Jetta TDI GLS silver
Kerma,
So you are saying on the PD they change duration... ok I have seen that map in PD files. But not the VE and they too feel a loss of power with hot fuel, like in your thread those using heated VO. So what were the VE doing without a duration adjustment?


From a table I found, from 15C to 65C, there is a 3% reduction in density.

So he would see a 3% difference at most if the fuel was hot. 3% of 200 hp is 6 hp... would it be that noticeable?
 
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Mikkijayne

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Audi S8
Believe it or not, there also is a provision present (present but inactive in most implementations ;) including the factory one) for the lower energy density of biodiesel...
Interesting... could you elaborate on that please? Can the ecu tell what fuel it's burning from its behaviour or is it a switch in the map?
 

steve05ram360

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Jul 22, 2008
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all over
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2011 2D Golf
Kerma,
So you are saying on the PD they change duration... ok I have seen that map in PD files. But not the VE and they too feel a loss of power with hot fuel, like in your thread those using heated VO. So what were the VE doing without a duration adjustment?


From a table I found, from 15C to 65C, there is a 3% reduction in density.

So he would see a 3% difference at most if the fuel was hot. 3% of 200 hp is 6 hp... would it be that noticeable?
I read earlier that its more than that 3% you noted... Read post #2

http://forums.tdiclub.com/showthread.php?t=20401

considering doing this mod to try to drop fuel temps some. Mainly to help cool the fuel before the injection pump and minimize the lubricating losses that apparently happen when temps get too high.
 
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