Eliminate Thermo Tee and fuel Filter Temporary for air leak?

cherrybomb

Active member
Joined
Dec 28, 2021
Location
Lwr. Mid. Tn.-Hsv. Al.
TDI
2003 Beetle TDI
2003 Beetle 1.9L ALH./ AT. Bought car with 186K miles, discovered a diesel leak in lower chamber of IP. Changed all fluids & filters and worn items. Replaced both Seals (O-rings) and reset IQ using VCDS Lite. Car ran great all summer. Changed fueling stations from (Al to Tn) and car began to take several trys to start and run. This was intermittent and continued for a while. Bought & installed a new Thermo Tee, but still slow to start upon cranking. Finally discovered the leak by diesel dripping at base of pump head. Obviously there was no problem with the original Tee I replaced. Resealed the Pump Head successfully using procedure suggested in many articles. Used a 12v. pump inline to prime the IP and lines, then proceeded to crank engine over and it bled nicely and ran. During the IP Head repair, we used a Strap Wrench Tool to turn crank pulley to get pump stroke at Max. Discovered the Serpentine Damper bad so replaced it also. Alt. Pulley was good and belt appeared new so it was reinstalled. Working in are of filter, we considered we may have disturbed the lines,Tee & clip so we removed and lubed the o-ring and reinstalled. No reason to suspect the lines,(rubber or metal) damaged and had been good prior to the Pump Head repair. The car runs great after it starts and will sometimes take excessive cranking to start now. Must be the Tee. Would like to bypass the entire filter assembly and temporarily install a inline diesel compatible filter to isolate the problem. Plan to use 5/16 clear filter and a 5/16 barb (return line) to eliminate the existing filter. Generally are the plastic Tees cracked or just the o-rings damaged? Have another new Tee with o-rings on order, but would like to ID the reason for this problem. Suggestions welcomed.
 

drucifer

Veteran Member
Joined
Dec 21, 2013
Location
fredericksburg virginia
TDI
2004 jetta sw tdi pd
If you tried pull the hoses off the tee they crack easily. I would do without the car for a day or two before trying to go around it. The car is at home where it's warm with food, bed and bathroom. When you reinstall the hoses use some silicone grease on all the nipples.
 

fatmobile

Veteran Member
Joined
Jul 16, 2019
Location
north iowa
TDI
an ALH M-TDI in a MK2, a 2000 Jetta, 2003 wagon
So you are seeing air in the fuel going into the injection pump?
If you are saying you suspect air in the fuel,
clear fuel lines will help you figure out where it is coming from.
Or if you even have air in the fuel.
Did you check VCDS again to see if anything has changed?

I noticed in VCDS when checking the timing graph.
It is graphed using fuel temperature.
Colder the fuel the farther the line rides to the left.
I'm not sure what happens when the fuel gets real cold.
Does it go off the timing graph? Or does the graph change?
When I mentioned my CAT fuel filter mod, Franko said the fuel temp (and the thermo T) is important.
 

cherrybomb

Active member
Joined
Dec 28, 2021
Location
Lwr. Mid. Tn.-Hsv. Al.
TDI
2003 Beetle TDI
Thanks for replies and suggestions. COLD is not a problem here. Tn. lows have been 20 degrees and compared to some of the others, do not consider this COLD. No clear lines on Beetles unless someone adds them I understand. Regarding VCDS, no more checks sine last time I ran it. No CEL or codes then. No CEL at this time. This is reason I suspect air leak. The silicone on hose sounds good. will try it. Will keep investigating since not prone to accept defeat :)
 

jettawreck

Top Post Dawg
Joined
Aug 2, 2004
Location
Northern Minnesota-55744
TDI
2001 Jetta and 2003 Jetta
I had the fuel sending unit develope a crack in the plastic base where the nipple (out going fuel) is molded to the base. For "testing" purposes in wouldn't worry about a temporary filter. Put some clear line on it and if you have air bubbles work your way back from the IP until you find the source.
It's not unheard of for the sending unit pick up tube to crack also.
 

Lug_Nut

TDIClub Enthusiast, Pre-Forum Veteran Member
Joined
Jun 20, 1998
Location
Sterling, Massachusetts. USA
TDI
idi: 1988 Bolens DGT1700H
There's no lift pump. The engine mounted pump sucks, literally. Any leak between the fuel tank and the inlet port on the pump could be letting air in. The fuel is pressurized from the pump outlet to the injectors, and is pressurized, but much, much less pressure, in the injector return lines back to the thermal T. Leaks in that part of the fuel circuit would show as fuel dripping out, not air getting in.

A quick test is to remove the hoses from the T and connect the hoses directly to each other. This will send surplus fuel straight back to the tank. Then add a short loop of hose to each side of the T to 'plug' those open ports. Presto! An "unheated" A1/A2 diesel filter.
 
Last edited:

lost1wing

Veteran Member
Joined
Jan 23, 2007
Location
USA, Georgia, Homerville
TDI
2003, 2003, 2002, 2000 ,2000
I had an injection pump that was the cause of my cold start problem. I got the car with 207k miles on it. It started great all summer long. When temps got below 40f, it just took a few more seconds to light off. I changed/ unplugged temp sensors with no change. No air in fuel lines. New seals on the pump. Put the pump on an iv just to rule out air bubbles, still no help. I stopped fooling with it. At 318k miles the injection pump failed. Found about 30 degrees of freeplay in regards to rotation, so I replaced it with another used pump and my cold start problem went away.
 

cherrybomb

Active member
Joined
Dec 28, 2021
Location
Lwr. Mid. Tn.-Hsv. Al.
TDI
2003 Beetle TDI
Verified no leaks on pump or rubber hose lines visually. Used my set of hose type clamps for rubber line and pinched off the inlet line into filter and the black rubber line return line hose behind filter prior to metal return line to tank. Allowed car to sit 48 hours, then removed the clamps, car started immediately. Have decided to eliminate the Thermo Tee and use the early In-Out filter and 5/16 line connector. Not cold here enough to be concerned about gelling. Would add Power Service treatment below 30 degrees. Seems this will solve my slow stat quandary. Thanks for suggestions.
 
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