Finished OM642 oil cooler seals, now BIG fuel leak - PeachParts Mercedes-Benz Forum

sfsegui · #1 12-14-2022, 04:45 PM

Decided to start a new thread because my “massive coolant leak” has been resolved. Unfortunately, while taking out the 2007 GL320 for the first substantial drive since I had buttoned up the oil cooler seal job and cleared all the codes (except for glow plug), I now have a considerable fuel leak.

Had been driving about 80mph for 10-15 minutes (actually thinking what an incredibly smooth riding vehicle the GL is) when I got off an exit, circled around, and re-entered interstate. Decided to “get on it” pretty good and after a few seconds, lost all power. Coasted back off interstate and came to a stop. Car was still idling, tried to creep out into traffic, vehicle started stumbling badly. Pulled back over and turned off. Got out and checked coolant because I was seeing smoke coming from back of engine. No coolant loss and whatever had happened/broke, I couldn’t see from top of engine. I was only a few miles from home, started up (no new codes), drove very slowly home, but there was no stumbling, hesitation, etc with vehicle.

Got home and popped hood and the smell of diesel was overwhelming. Was still coming out from the bottom at a pretty good clip as well (actually suffering from the diesel headache as I am writing this).

Pictures below are of underneath vehicle about 10 minutes after it was shut off. Pretty large amount of fuel.

Looks like I get to pull a bunch of stuff off again trying to find what let loose. There were no signs of any of the fuel injection connections that I had removed during the oil cooler seal job letting go. Fuel filter, low pressure lines all snug. My thought is that the leak source may not be that big, meaning that if it is a hard line it is such high pressure that even the smallest opening will allow a lot of fuel to escape.

I couldn’t see a thing from the top pretty much completely dry. As dry as the top of the motor is, when inspecting from underneath, everything is soaked in diesel. The smell brought back memories of when one of the steel lines broke on my 602 and I had to drive 40 miles home with that smell coming in the cabin.

I am trying to think where any fuel lines are toward the rear of the engine that I may have messed with. Any ideas or suggestions on where to look are greatly appreciated.

and finally, the view from front of vehicle

jay_bob · #2 12-15-2022, 06:49 AM

The LP fuel circuit on these is pretty simple. The fuel loop to/from the tank enters the engine bay from underneath at the bottom left (all left/right references are per standard, your steering wheel is on the left).

It hits a couple rubber lines that jump over to the engine and then a couple steel lines up by the HP pump. One line (supply) heads over to the fuel filter and then into the HP pump. The other line (return) captures the return lines from the injectors, the fuel pressure regulator (front of left rail) and I think a relief from the HP pump. The returned fuel all goes back to the tank.

I wonder if you lost a return line? The assembly can spring a leak after time and miles. In fact I just ordered 2 of the return line sets and o-rings to replace the ones on my 2008 cars (my SUV that I did the cooler seals in 2016 and my son's E320 that I am about to redo the seals on next week).

When you made up the LP fuel lines on reassembly, did you reuse the clamps or use new ones? Those Oetiker clamps are technically single use only.

Thought of something else, on both my 2008s, the rubber lines terminating at the fuel filter developed leaks at the filter, and I have had to replace them. Also the water in fuel sensor can get a leak and I had to change that on both cars too.

Murkybenz · #3 12-15-2022, 11:02 AM

Water in fuel sensor can have the o rings replaced ( use 16.5mm internal diameter by 2.5mm cross section ) which are a tighter fit , most o rings supplied with on642 filters are not quite up to the job and its too easy to get the water sensor fitted and then they eventually leak and being on the low pressure side does not flag up a pressure loss which would cause ecu to shut down engine.

87tdwagen · #4 12-15-2022, 12:59 PM

That's a pretty decent amount of fuel.
Retrace ALL of your connections, even the hard line fittings. IF unsure where, you can also wrap or lay paper towels over any fuel lines, run the engine and inspect the paper for signs of wetness. It is likely something that was moved, or loosened or otherwise tampered with during the cooler seal job IMO.

jay_bob · #5 12-16-2022, 12:54 PM

My experience, the water in fuel sensors developed internal cracks and leaked out the plastic housing, so it wasn't just bad o-rings.

Remember the LP side is pressurized to 50-60 psi while running (from the submersible pump in the right side tank) so it's not like the old cars where it's all under vacuum.

sfsegui · #6 12-16-2022, 05:56 PM

Just got back in town from work. Going to dive in tomorrow morning. Thinking it could be one of the plastic “click tops” of the return lines. I am sure I clicked all of them down upon reassembly but I believe they have a small o-ring in them. While researching, I read several threads that were very similar to my situation. Will find out tomorrow hopefully when I remove air filters and bat wing. Thanks for all the input and will report back soon.

sfsegui · #7 12-17-2022, 06:22 PM

Removed air filters, bat wing, etc. Turned vehicle on and fuel pump started, almost immediately could hear leaking coming out from underneath. Impossible to tell where it was coming from underneath as it was draining and running down the bell housing. Nothing obvious from top side. Looked closely at all injector hard line connections and inspected the return lines. The driver side closest to the firewall return line fitting was wet, but not as wet as I would expect with the amount of fuel leaking.

I pushed down on the return line and to my shock I heard an audible click! I know for a fact that I checked and double checked for the “click” when I installed. Turned on again, no leaks. My thinking is that since I forgot to install the new tiny o-rings upon reassembly, the old o-rings just couldn’t hold up to the fuel pressure when I gunned it. Regardless, I put all new o-rings in, clicked everything down, and buttoned up.

Had a large number of codes as I started the vehicle without the bat wing and air filters to make sure no leaks were present after the new o-rings. Cleared codes and went for a drive. No leaks. Took on interstate, got up to 80-85 mph, no loss of power. While I was very nervous, I did “get on it” when I hit the merge lane and I am very pleased to report no power loss/fuel loss.

Hopefully this hiccup is behind me. Amazing how that small of an o-ring can cause such a large issue. Lesson definitely learned.

Now just need to fix the glow plug module wiring issue and go by jaybobs so he can do the adaptions and hook it up to his xentry.

Still have a nagging little “clunk” from the front suspension on deceleration around 10mph, a couple interior things to address (broken vent control, rear entertainment system), but for the most part I am feeling pretty good about the vehicle.

Thanks again for everyone’s help as I begin to understand the OM642.

Benzadream · #8 12-18-2022, 10:17 AM

Congrats on your success! I know it must be an incredibly great feeling! I followed along as you tackled this project and can honestly say how impressive your abilities at organization and of determination really are. Amazing and outstanding! My hat's off to you sir! I was actually quite relieved when you were able to track down the fuel leak and remedy the problem so simply. The ups and downs with twists and turns made the entire thread seem like an "action thriller spy novel" lol.
Thanks for the great ride! (obviously, I lead a pretty boring life and need to get out more...haha)

ah-kay · #9 12-18-2022, 10:52 AM

This is one of the reasons that I like the om648 more than the 642. Everything is on top and you can spot the return line leak within seconds. Don't need to remove anything except the cosmetic cover. The return line has a metal clip to secure it. Oil cooler is not buried deep inside. Anyway a job well done.

sfsegui · #10 12-19-2022, 10:05 PM

Appreciate all the kind remarks. I have to say that there were several moments of “what have I gotten myself into” but with the help of this board and especially fellow member jaybob, I am very happy with the outcome.

Believe I have resolved the glow plug light issue as well, a good cleaning of the connectors at the module and the glow plug light has not returned while driving.

Next on the list is to change motor and transmission mounts. Hopefully this will resolve the clunk from front end I keep hearing/feeling. Ruled out suspension issue as the front end was completely rebuilt (ball joints, airmatic struts, sway bar bushings, etc) 6 months prior to purchase.

Again, I want to thank everyone who commented, even just to say they enjoyed following the thread as it helped to motivate me to finish the job.

Hope everyone has a Merry Christmas and a fantastic New Years!