Club Touareg Forum banner
21 - 31 of 31 Posts

·
Registered
Joined
·
193 Posts
lol i dont subscribe to the mass paranoia...ive filled tdi for 15 years below the fuel light almost every tank, never had a single issue with the 5 or 6 ive owned...fuel quality is far more of a factor by far
Since the issue is cited as the HPFP overheating, I suspect the ambient temperature you drive in has a lot to do with it. U.S. desert southwest, be careful. Canadian winter, not so much.

The engineers who designed the engine put the fuel return line in there for a reason. They knew the engine cooling requirements, so I will indulge them and be sure to feed cool fuel into their cooling system. I usually fill between 1/8 and 1/4 tank. Very rarely below 1/8, partly for this reason, partly because the low fuel warning hides some of the info being displayed (like odometer, which I kinda need to track my miles driven for tax purposes).
 

·
Registered
Joined
·
664 Posts
:mad:
I'd like to raise the BS flag and wave it HARD.
I'd also like to challenge anyone who claims that those of us who run our tanks low are sucking hotter fuel into our pumps compared to the fear mongrels that fill at 1/2 tank or whatever....

Please feel free to log your fuel temps in whatever climate\condition you'd like and lets compare your fuel temps at >1/4 tank full with anyone else who's willing to play along and log theirs at <1/8 tank full. I'm guessing the difference will be negligible if it even exists!

Please remember that CP4.x pumps are used all over the world, not just in Canada with "cold fuel", by numerous manufacturers, etc..... even in places like Australia or Africa or South America where it can be hotter than in the USA.

If you spend any time reading or researching the CP4.x failures, you will see that the number one contributor is lack of lubricity, followed closely by things like miss-fuelling, improper maintenance\bleeding, foreign object damage, etc.

This hot fuel tank urban legend is just that.... the fuel tank is not a heatsink and it was never designed to be used as one.
 

·
Registered
Joined
·
193 Posts
:mad:
I'd like to raise the BS flag and wave it HARD.
[...]
This hot fuel tank urban legend is just that.... the fuel tank is not a heatsink and it was never designed to be used as one.
I'm coming from a maritime background. When I worked at a shipyard, the diesel engines we installed most definitely used recirculated fuel to cool the injectors.


I just assumed it was the same for diesel cars - that due to the smaller engine parts they relied on fuel for cooling rather than drilling channels for cooling water in everything like the injectors and HPFP. If they don't work like that, I'd love to know for sure. I plan on driving my TDI on a 6000 mile cross-country trip this summer. If I can drive until the tank is nearly empty that'll give me an extra 100-150 miles between refills, and make some of the drives through remote areas easier.
 

·
Registered
Joined
·
664 Posts
Modern vehicles systems, especially those on the Touareg are far different than tractors, ships, generators, etc.
If you spend some time reading about what you're driving and what kind of tech it has, you will understand why you're simply jumping on the doomsday bandwagon without any merit.

SSP said:
FuelTemperature Sensor G81
The Fuel Temperature Sensor G81 is located in the fuel supply pipe to the high-pressure pump. G81 is used to determine the current fuel temperature.

Signal Usage
The ECM uses the Fuel Temperature Sensor G81 signal to calculate the fuel density.
This serves as a correction variable to calculate the injection quantity, to regulate the fuel pressure in the high-pressure accumulator, and to regulate the quantity inlet to the high-pressure pump.

To protect the high-pressure pump against excessively high fuel temperatures, the Fuel Temperature Sensor G81 is located in the fuel supply system. In the event of excessively high temperatures in the fuel supply system, the engine’s output is limited in order to protect the high-pressure pump. As a result of this, the quantity of fuel to be compressed in the high-pressure pump is also indirectly reduced and the fuel temperature is lowered.

Effects of Failure
In the event of Fuel Temperature Sensor G81 failure, the ECM employs a fixed substitute value for calculation purposes.
 

·
Registered
Joined
·
193 Posts
Modern vehicles systems, especially those on the Touareg are far different than tractors, ships, generators, etc.
If you spend some time reading about what you're driving and what kind of tech it has, you will understand why you're simply jumping on the doomsday bandwagon without any merit.
These weren't WWII-era tractor motors. They were state of the art high-performance diesel engines used on high speed catamaran ferries. The old ones used to have channels cut into these parts for coolant to flow. Modern diesels use the fuel as coolant for the hard-to-reach places like injectors to increase efficiency (pumping coolant through tiny channels requires more energy).
To protect the high-pressure pump against excessively high fuel temperatures, the Fuel Temperature Sensor G81 is located in the fuel supply system. In the event of excessively high temperatures in the fuel supply system, the engine’s output is limited in order to protect the high-pressure pump. As a result of this, the quantity of fuel to be compressed in the high-pressure pump is also indirectly reduced and the fuel temperature is lowered.
That makes it sound like the "urban legend" is true, and it is possible to damage the HPFP if you let the fuel levels drop too low while driving in hot climates and/or with heavy load. Best case it results in the engine going into limp mode. Worst case the sensor fails or is faulty, and you end up with a multi-thousand dollar repair.
 

·
Registered
Joined
·
664 Posts
That makes it sound like the "urban legend" is true, and it is possible to damage the HPFP if you let the fuel levels drop too low while driving in hot climates and/or with heavy load. Best case it results in the engine going into limp mode. Worst case the sensor fails or is faulty, and you end up with a multi-thousand dollar repair.
Do whatever makes sense to you and gives you the most piece of mind.
If I were to use that mentality, I would never use the full output of my Touareg as a sensor might fail so all the electronic controls and systems may not act to save the engine from hurting itself... so I would just creep around in "safe mode".

I think I might just quit pulling RV Trailers and only use my hitch for bike carriers.... I'm sure VAG engineers messed up on that design aspect too, and I don't want to risk blowing up my rig from stressing it by using it as it was designed, etc.

Gotta go now... it's hot today, and I'm down to 7/8 of a tank.... my HPFP might blow up if I don't rush to refill to keep that fuel cool. :rolleyes:
 

·
Registered
Joined
·
193 Posts
Do whatever makes sense to you and gives you the most piece of mind.
If I were to use that mentality, I would never use the full output of my Touareg as a sensor might fail so all the electronic controls and systems may not act to save the engine from hurting itself... so I would just creep around in "safe mode".
I'll probably pay it less heed when I'm driving around home. But unfortunately it's not gonna help on my trip. If I'm in the desert 50 miles from the nearest service station, even just going into limp mode will mean getting a tow. While a sensor failure would leave me stranded with the trip on hold for multiple days while I wait for parts and repairs. Plotting my trip so I always fill up before 1/8 of a tank seems like an easy way to completely eliminate that possibility.

Gotta go now... it's hot today, and I'm down to 7/8 of a tank.... my HPFP might blow up if I don't rush to refill to keep that fuel cool. :rolleyes:
Alright. That convinces me that you don't understand the physics going on here.

The danger here isn't constant. It doesn't even scale linearly. When you're using the fuel reservoir as a heat sink, the temperature increase of the fuel scales (to a first approximation) by the inverse of the mass of the remaining fuel. You're pumping the same amount of heat energy into a smaller and smaller heat sink. If a full tank results in a 5 degree increase in temperature, a half tank will result in a 10 degree increase. A quarter tank a 20 degree increase. 1/8 tank a 40 degree increase. 1/16 tank a 80 degree increase. So the problem gets much worse much more quickly when you have small amounts of fuel remaining.

(It won't be quite this bad because heat transfer from the fuel to the air will scale linearly with temperature differential. But it should be obvious that a geometric increase in temperatures countered by a linear decrease in temperatures, results in a net increase in temperature.)
 

·
Registered
Joined
·
537 Posts
:mad:
I'd like to raise the BS flag and wave it HARD.
I'd also like to challenge anyone who claims that those of us who run our tanks low are sucking hotter fuel into our pumps compared to the fear mongrels that fill at 1/2 tank or whatever....
Ive been fighting this stuff since early 2011 when i bought a brand new tdi jetta, which according to the internet the fuel pump were just exploding all over the place due to this.....over the 6 years i owned it i ran every tank to empty, including one that took 58 liters in a 55 liter tank, Never once did it ever have an issue, i personally know the current owner and its nearing 600k kms and still driving great....furter more its stage 3.5 malone so the pump has been running virtually maxed out since i tuned it in 2012.

Ive since owned 2 more common rail jettas..have 5 at least friends with them...and i own 2 touaregs that are common rail and have never seen a fuel pump issue
 

·
Registered
Joined
·
664 Posts
@Solandri
It's Friday and I'm done arguing with people this week. If you really want to, go ahead and read everything up above. If it makes you feel better to claim that I don't understand some aspect of it, sure.... no one knows everything.

Regardless, do me a favour and read some SSPs on your Touareg's injection system. After that, read some articles on your choice of many injection outfits, their teardown\rebuilt process and investigations, and their root cause analysis on what cause the failure (in all these timebomb CP4.x pumps). If after all that you believe that you are still relying on the fuel level in your tank to safeguard your HPFP, by all means, go ahead and fill at whatever level you're comfortable with.

Just between @tdimark69 and myself, we've already confirmed, with first hand experience that we have repeatedly ran our vehicles low on every single tank for many miles combined.... if after all that you're still sweating this gas tank heatsink nonsense (which I specifically said it was never to be a heatsink above), there's nothing that can be done.

I'm telling you, just drive more, worry less..... especially about how early you need to refuel :p
 

·
Registered
Joined
·
8 Posts
If you run one of these to empty prepare for a lot of expensive repairs. I guess I understand the curiosity,but is it really worth blowing up the HPFP ? You can precisely figure your mileage buy the fill up method by zeroing the mileage counter when you fill and how many liters it takes, EZZEE,peasey. My 2016 gets filled at about a quarter of a tank and takes about 20 gallions.
If you get that much air into the HPFP it will be throwing error codes for fuel pressure being out of range and will be running rough. If you ignore the warnings then yeah of cause you will damage but not for having 1/8 of a tank.
 
21 - 31 of 31 Posts
Top