Running a TDI empty.

[DT]

Hey fellow Diesel Dudes,

I haven't been following the forum lately, too busy driving.

I did do something different the other day that I would like to share, just for kicks I ran my TDI dry.

The results:

Total distance traveled: 1417.3 km = 880.7 miles
Distance traveled on reserve: 205.6 km = 127.8 miles
Total fuel used: 63.78 L = 16.85 gallons
Fuel economy: 4.5 L/100 km = 63 MPG

I was really impressed with distance I traveled on reserve. The needle dropped to empty quite quickly, but the car just kept going.

After dumping in a spare can of diesel, I had to crank the engine about 6 times to get the fuel system reprimed and I was off.

DT
1999 A4 Silver Jett GLS TDI

 

[Ted Strong]

Interesting. I know a guy with a John Deere diesel tractor, and he told me that you never want to run a diesel dry. I think he said something about air getting in the system. Perhaps it's not a problem with our cars though.

 

[BKmetz]

The fuel filter on the TDI cannot be sucked dry. The fuel pickup is in the middle of the filter just under the filter medium. The bottom half of the filter is an empty cavity for water to collect.

If anyone runs the car out of fuel, prime the fuel filter before starting. This will lessen the amount of air the fuel pump has to suck before getting fuel. Priming the fuel filter is easy. Remove the fuel recirculation valve off the fuel filter and fill through the hole. Add about a pint of fuel. A completely empty filter will almost hold a quart/liter.

Brian, 97 Passat TDI
bpkmetz@crtelco.com

 

[DT]

Ted,

I'm aware of the problems with larger diesel engines. You never want to run them dry, big hassel or big bucks to get the fuel systems reprimed.

I once ran a 2 1/2 ton truck dry and the only way we could get it started and keep it going was to stop every 5 km and refill the fuel filter, the rest of the system refused to reprime (it was a long trip to the garage).

That's not the case with our TDIs (granted at the first of sign of engine fade, I turned the ignition off and costed onto the shoulder), the system is self priming as long as you don't drain the lines and you put in enough fuel (4 L worked for me), to refill those lines. And you also have crank it a few times to prime/pressurize.

DT
1999 A4 Silver Jett GLS TDI

 

[dparnell]

Most diesel engines do not have electric fuel pumps---if you run them dry, you have to purge the system of air---it's called "bleeding the injectors"---you loosen the fitting at each injector and turn the engine over until fuel come out, then tighten fitting and start engine---this reprimes the pump and purges the system of air---TDIs have electic fuel pumps that prime the injector pump---it doesn't hurt to run out of fuel and you don't need to fill your fuel filter.

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[Ric Woodruff]

You don't need to fill the fuel filter, but it helps; it saves quite a bit of cranking (especially important if your battery is a few years old). I once ran out of fuel in my '85 Escort diesel (2.0 Mazda engine). I added a gallon, cranked a little more than normal, and was on my way - no problem.

 

[SkyPup]

I don't quite understand how running the engine dry doesn't fill the pump and injectors with air?
I know the fuel filter has the recirculating set-up to the tank, so that air bubbles on the top are skimmed off to the tank while the motor is running, but if the pump and injectors get air into them, I can't see how they can self prime themselves without loosening an injector or something to bleed off the air.
BTW, a good way to permanently ruin your BOSCH VE VP 37 fuel pump on your TDI is to crank the enigine while there is no fuel in the pump!

Remember that this pump relies on fuel for lubrication and it is an extremely high pressure unit, the fastest way to ruin it besides clogging up the fuel filter and introducing crude into the pump is to crank the engine to prime the pump while the pump is empty. This is a serious no-no.

You may be able to get away with it in the short run, but in the long run it will catch up with you. Those injectors take an awful lot of pressure to function properly, without the pump working top notch, the injectors don't stand a chance.

 

[dparnell]

I could be wrong but I always assumed the electric pump created a vacuum, sucking the fuel in and expelling the air into the combustion area. My Lister-Petter generator has a 15' clear fuel line---as I was turning it over for the first time, I watched the fuel lurch forward on each compression stroke until started. On my Onan(without fuel pump) the fuel doesn't move until you crack the injector fittings.

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[mickey]

If cranking the engine with a "dry" injector pump will ruin the pump, then we're all in trouble. I primed my new filter when I changed it, and there was still about 2 minutes of cranking involved. (Not continuously! Give it a rest every 15 seconds.) Actually, the engine started instantly, then died after about 30 seconds. After that there was some serious cranking involved.

The injector pump is turning at very low rpms while you crank the engine. There is some residual fuel still in there to provide some lubrication. I seriously doubt you could hurt the pump unless you crank and crank for hours on a regular basis.

Anybody read DT's original post? He ran it dry, and it started right back up after a little cranking. No big deal. Certainly, running the thing dry is to be avoided. And it's a major problem with some diesel engines. But with a TDI it's just a minor, temporary inconvenience.

-mickey

 

[SkyPup]

If I remember correctly, the RB manual states specifically not to crank the engine w/o fuel in the pump. But as it is apparent here, it is to be avoided anyways except in an emergency.

 

[BUG*PWR]

Under the RB manual maintenance section replacing a fuel filter for an ALH engine. I was surprised to read no mention of priming or starting upon replacing the fuel filter. The only statement was to check for leaks from the inlet outlet lines after starting.

 

[BKmetz]

dparnell,

The TDIs do not have an electric primer pump. The injection pump has an electronic fuel regulator on top which works with the ECU. The injection pump has to suck the fuel all the way from the fuel tank.

Last year the wife ran the Passat out of fuel. I poured a few gallons of kerosine in the tank and primed the fuel filter. The engine turned over for about ten seconds before it fired.

I don't know of any practical way to purge the air out of the fuel lines.

Brian, 97 Passat TDI
bpkmetz@crtelco.com

 

[mickey]

SkyPup: I'm sure the manual says that, but if anybody has any ideas on servicing the filter without requiring a little "dry" cranking I'd love to hear it. I just can't imagine the thing is that fragile! If it's not primed, then it's just compressing air. That is a lot easier than trying to force fuel (which does not compress) through little tiny injector nozzles. In my opinion, the injector pump is practically freewheeling during the cranking period. And like I said, there's going to be some residual fuel in there to lubricate things. (Especially for those of us who use lubricity additives!) I think the RB manual's warning was more of a "don't be a dumbass" disclaimer than anything. Unnecessary dry cranking is certainly to be avoided (that would include deliberately running the thing out of fuel), but a couple of minutes of cranking every 20,000 miles can't possibly make a difference. Hell, you could idle the engine without any motor oil for that much time and not cause any significant harm! (Just ask the "ProLong" guys.)

-mickey

 

[KO]

With a vehicle that gets 600+ miles on a tank of fuel. How can anyone run it out of diesel? Maybe some people never look at their gauges, I have always made it a habit.
I mean really, you would have to have odometer, fuel gauge failure to justify running out.

Besides, the blue dash lights are cool!

 

[ENUTPEN8]

DT, I thought the fuel capacity on these things was 14.5 gallons. How did you use 16.85? Those fuel compressors are not available in my area...Nick at Night

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'71 Super Beetle w/Hurst & header; '99 New Golf GLS TDI auto.

 

[DT]

ENUTPEN8,

It's the classic 1/4 throttle continuious venting technique, guaranteed to piss off the gas bar attendant and anyone else that might be waiting to fill up with diesel. I fill it till the diesel is spilling out (that explaines the 16.85 gallons

). Seriously you can really extend your crusing range by topping right up, my fuel gauge does not start moving till after 300 km = 185 miles.

And KO, I don't make a habit of running it dry, I wanted to find out how far I could go. Now we all have a bench mark at the expense of my fuel pump Skypup

.

DT
1999 A4 Silver Jett GLS TDI

 

[KO]

I love a good experiment, as much as the next guy. But, there are too many variables, I believe, for this to be an accurate test. I mean, would we all operate our TDI's in exactly the same manner? Is our tire design, pressure the same? Did we drive in the wind, or against it? Did we shift at the same rpms? Do we all use the Magic Cetane enhanced diesel formula? Do we use the a/c, if so do we turn it off as we use the drive through at McDonalds?

I am no saint, I have ran my vehicles low to see what the warning light looks/sounds like, but running a new car, with a fuel pump this expensive out of fuel is just silly.

Please, don't misconstrue my response, "I" think it's silly.

Whatever, blows your skirt up, is fine with me!

[This message has been edited by KO (edited September 03, 1999).]

 

[mickey]

I left work this afternoon with a 65 mile drive to my house awaiting me. The Low Fuel light came on almost immediately. I made it to the Flying J 3 miles from home with no problems. I filled the tank of my NB clear up to the cap, and it only took 14.9 gallons. I know I had plenty to spare, because I once squeezed 15.5 in there with lots 'o venting. I assume DT lives in Canada, and is using Imperial gallons, because 16.85 gallons and 63 mpg doesn't sound possible to me, unless Jetta tanks are much bigger than NB tanks. Or maybe the "reserve" is a whole gallon bigger than I thought.

-mickey

 

[Jimmy]

DT - Clarification please: When you say "reserve", do you mean from time when the beeper goes off?
Thanks,
Jimmy.

 

[Ric Woodruff]

Mickey, when I changed the fuel filter in my '98 Jetta, I primed the fuel filter to the top. When I went to start it, it fired right up and ran perfectly normal, as if there was aboslutely no air in the system. I can't understand why yours took a lot of cranking if you primed the fuel filter.

 

[mickey]

Perhaps because I am an idiot and lack your superior automotive skills. Or perhaps because the filter is a different design. My "late" '99 NB is different than an "early" '99 NB. The filter contains all kinds of valves and thermostats and whatnot to reroute the fuel when the temperature is cold. It's difficult, if not impossible, to completely prime it. You can get close, but some air is still in there.

-mickey

 

[DT]

Jimmy,

Yes, that was from the time the beep went off and the light came on. I admit I was driving in economy mode from that point on 90-100 km /h = 56-62 MPH, but the distance still suprised me.

And Micky that is in US gallons, maybe the reserve tank is bigger then we thought.

Bottom line is, when my fuel light comes on and the beeper goes off (sending me through the roof)I know I can easily drive 160 km = 100 miles +.

DT 1999 Silver Jett GLS TDI

[This message has been edited by DT (edited September 04, 1999).]

 

[SkyPup]

STRAIGHT FROM THE HORSES MOUTH:

BOSCH VP VE 37 - FUEL INJECTION PUMP A3 and A4 TDI (ALH models) 1995-2000.

CAUTION: DO NOT ATTEMPT TO START ENGINE WITH A DRY DIESEL INJECTION PUMP. SEVERE DAMAGE WILL RESULT. ALWAYS ENSURE THAT PUMP IS FULL OF FUEL BEFORE CRANKING.

Install fuel delivery supply line onto the fuel filter and attach supply line to the BOSCH injection pump. Now, using a hand vacuum pump, draw the fuel into the pump to prime it. Empty pump requires 180 mls of diesel fuel. Reinstall fuel line and start motor. Check lines for excess air bubbles.

Do not crank engine with an empty pump as severe damage will occur. Running the tank dry is not a good idea, even if you manage to get it away with it once in an emergency.

[This message has been edited by SkyPup (edited September 09, 1999).]

 

[mickey]

That's excellent advice, but I'm sure it refers to re-installing a new or rebuilt pump. The pump will not be "dry" after a filter change, since the filter is higher up than the pump. No fuel spilled out of the lines when I changed my filter, therefore the pump still had fuel in it. I was unable to completely eliminate all air from the new filter, and the pump lost its prime after a few seconds of pumping when the air bubble reached it, but there was still some fuel in there. It will never be "dry". Just my opinion, of course, but I can't see any alternative to a little cranking. You're going to get some air in the line, the pump is going to lose its prime temporarily, and you're going to have to crank the engine a little bit. Not much, if you do the job right, but at least a little bit. Perhaps it would be a good idea to give the pump an extra blast of Mystery Oil prior to changing the filter, just to make sure.

-mickey

 

[Frank TDI]

Mickey, I have heard that you should NOT add Marvel mystery oil to the fuel because it damages the seals in fuel system. Have I gotten the wrong info? Frank

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Frank TDI

 

[mickey]

I was sort of half kidding about the MMO. I bought some, but it looks way too much like automatic transmission fluid for my tastes. (That is a big no-no.) SkyPup uses it, and nothing has blown up yet.

-mickey

 

[SkyPup]

I use MMO all the time, so far no hassles.

The pump warning was as Mickey stated, changing out the fuel filter is not the same as running the fuel tank out dry. Changing out the fuel filter is not the problem, running the tank dry and then restarting without sucking fuel into the pump first is the problem. Similar to rebuilding the pump, which indeed may be the expensive result!

 

[mickey]

Make sure that when you replace the fuel filter you do the best you can to prime the pump. Installing a dry filter will result in a VERY extended period of cranking. I'm sure that wouldn't be a good thing.

-mickey

 

[Boswell Bear]

These things have a manual lever or anyhting for priming the pump? Used to have one on my Cummins. Only used it once, in Alaska, but was handy to have the little lever to pull. The Bentley manual say anything about how to prime it? Like is a hand vacuum pump the same as a suction pump, and where does it connect? (Started carrying one just to get the oil back out of the sump after the dealer overfills it each time he changes the oil.)

 

[Tazzman]

I think this is a NO BRAINER
dont start a TDI without fuel primed.
DONT run it dry, If in Emergency follow step's to put fuel where it belongs.
If you want to take the big risk go for it.
But nobody should run out of gas.
Extreme exceptions which I wont go into.

Unless you want to start another querry
or poll,
On excuses of running out of fuel
Or the biggest bone head move.
or what ever... what about it SKYPUP?

Tazz

simply miffed at silly people who do silly things.

JS SMKN