LB7 Big time fuel leak when towing

[Gaztech]

This fuel leak only occurs when towing.. Good size leak on my 04 and shows up by starter. Fuel filter is tight no fuel on firewall and fuel logs on top look good including tubing to injectors. Leak appears to be coming from between block and head by rear glow plug passenger side. Pressure washed everything and road tested no trailer 65 miles no leak. Hooked up trailer 6 miles and underside of passenger side soaked ? Any help been chasin this one 2 weeks now..
Thanx Fellers..........

[Mark Rinker]

Welcome aboard - you are in the right place to figure this out...


First of all, this doesn't sound good at all. Not a common problem description around here - in fact the symptoms sound like a combination of two more common conditions - 1) you obviously have a head gasket leak and 2) its may be combined with a bad injector, that is dumping lots of raw fuel.


Some questions:

• What year and how many miles on your LB7?
• How many miles on this set of injectors?
• Stinky white exhaust smoke present at idle?
• Is oil level increasing (fuel dilution)?
• Losing any coolant? I.E. coolant puking out of overflow? Any erratic water temp readings or cab heater operation?
• Any unusual sounds during loaded acceleration, or increase diesel knock?
• Lastly but very importantly - are you 100% certain its diesel you are seeing at the gasket, and not coolant?

One theory - especially if you have a 2001 Duramax and/or high mile injectors - would be a failed head gasket on that cylinder, due to the presence of LOTS of raw, unburned fuel.

In any case, based on your description, I'd stop observing it, and start fixing it - before you are searching for a new engine!!!

[Gaztech]

Truck is an 04 with 68K on it, and have installed 3 injectors number
6-7-and 8 @ 55K. No smoke at idle and runs like a top, with no unusual sounds. Oil level is OK and coolant is on the button. Water temp runs always at 200 and seldon moves. No unusual sounds, and have had 2 other mech's confirm it's diesel that we have all over us. I've been told that these heads run fuel (injector return) through them and to the block and out the banjo fitting in front of the turbo to the tank for return. If the gasket is leaking at the head I could be leaking fuel here Back of the starter is damp and up against the block. It's a mystery and we have just begun to beat this dog. Also the injectors were flow tested in the last 90day and the return rates and performance was OK.. then...
The truck hasn't been leaking at all unless loaded with my 5th wheel (9K pounds), and temp is always OK.
Thanx for the time to reply.. Gaz

[DmaxMaverick]

In all likelihood, the fuel rail or associated connection. Fuel pressures are at their highest (and longest sustained) during towing episodes. Underhood temps are up, too. The fuel return should be fairly stable under all conditions, unless the fuel filler cap has failed (higher return rates and temps with no pressure release can exploit any leak).

[UndergroundDmax]

Fuel filter is tight but is it dry? I have seen some of the fuel filter housings leak due to a bad o-ring.

Also, are you 110% its fuel? There is a plate with two bolts in it rigt above the starter and behind the up-pipe, if that gasket goes bad under the plate it will leak coolant out of that spot and soak the bottom of the motor.

[Kennedy]

Truck is an 04 with 68K on it, and have installed 3 injectors number
6-7-and 8 @ 55K. No smoke at idle and runs like a top, with no unusual sounds. Oil level is OK and coolant is on the button. Water temp runs always at 200 and seldon moves. No unusual sounds, and have had 2 other mech's confirm it's diesel that we have all over us. I've been told that these heads run fuel (injector return) through them and to the block and out the banjo fitting in front of the turbo to the tank for return. If the gasket is leaking at the head I could be leaking fuel here Back of the starter is damp and up against the block. It's a mystery and we have just begun to beat this dog. Also the injectors were flow tested in the last 90day and the return rates and performance was OK.. then...
The truck hasn't been leaking at all unless loaded with my 5th wheel (9K pounds), and temp is always OK.
Thanx for the time to reply.. Gaz

Always go back to the last place you/they were messing around.

[Gaztech]

Gentlemen

Thanx for the help as the 04 is on the rack again today
with the top 3 Duratechs putting their heads together.. Detailed description went with the truck and hoefully this helps. We are trying
to GETTER ER DONE this time.. Gaz

[Gaztech]

Durmax is back off the rack and the troubleshooters report a leak on the HP fuelrail for #5 was leaking.. The Duratechs drove the vehicle with no problem and the diagnostics attached.. NO LEAK so they returned and ramped up the pressure to 25K and the leak appeared. Their tool can control pressures, turn injectors on and off, and do a number of tricks. So hopefully this closes this story and Thanx to all for the reply's...
Gaz

[More Power]

Thanks for the followup.

Jim