diesel newb question: leak at glow plug? - PeachParts Mercedes-Benz Forum

Yak · #1 09-04-2009, 10:04 AM

I'm trying to isolate and stop as many of the leaks on my '83 300CD as feasible. Right now I've got it down to 4 identifiable and fixes for some of those are on the way.

The areas around the #3 and #4 glow plugs look like they are currently wet, or have been in the recent past. #3 is hard to identify the source and it might be the fuel lines above the glow plug or the large connection directly forward of the GP, but #4 has a spot about the size of a quarter directly centered on the GP with no trails of fuel or oil from anywhere else. #1,2, and 5 are all dry.

I've searched/reviewed the forums, to include the GP for dummies thread, but can't find the specifics about a leaking GP using search terms like "leak" and/or "fuel" and/or "glow plug" and/or "compression".

Questions: Are there O-rings in GPs that fail or wear out? I could not see any indication in the 617 engine manual or in online parts supplier.

What is the part/sensor in front of the #3 GP? Hex nut fitting screwed into head, single wire electrical connector (yeah, I'm lazy on that one...)

I have no symptoms or hard starting issues and just want to know if this is something to place on the bottom of my "to do" list. I have no record of glow plug maintenance from the PO, so it is possible the spots are from penetrating oil or externally applied in a effort to remove the plugs in the past, but the thread tips are a bit rusty, so it doesn't look like the nuts have been removed recently.

I have not done a compression test yet, but plan on getting around to that with a before/after valve adjustment. I don't have any compression gauges, but see they are available as loaners from O'Reilly or AutoZone. Are these loaner gauges suitable for testing on the 617 motor?

Right now the small fuel leak at the primer pump gasket and the leak at the oil filter stand are higher on the list. I figured I would try to get my "while I'm in there" considerations done early.

rrgrassi · #2 09-04-2009, 10:11 AM

Sounds like the return lines are weeping. Replace those first. Also check for leaks while the engine is running, as sometime the hard line can weep if they are not tight on the injector housing.

Olivier · #3 09-04-2009, 10:12 AM

My glow plugs just sit on the head, no washers or Orings.
Did you try pulling them out, clean the area and put them back?
Olivier

rrgrassi · #4 09-04-2009, 10:15 AM

Quote:

Originally Posted by Olivier

My glow plugs just sit on the head, no washers or Orings.
Did you try pulling them out, clean the area and put them back?
Olivier

The GP's on the OM616/617 are parallel with the ground. Fuel has to run down from the injector area to get to the GP.

vstech · #5 09-04-2009, 10:17 AM

it's unlikely for a leak to occur from the GP's. I'd focus on the injectors, and the valve (cam) cover gasket, that and the oil fill seal, and the crankcase vent connection. I've even seen a few where the injector shields were reused, and fuel squirted out from around the injectors...
like said above, change the fuel return lines, clean everything, look for fuel.
change whatever is wet.
fun fun fun.

Yak · #6 09-04-2009, 07:14 PM

The return lines appear to have been weeping. It was probably early days though.

The fuel was apparently trickling out the downward curve on the #3 to #4 line and collecting on the GP electrical cord. It wicked along the cord and was deposited onto the # 4 GP. Since there's not supposed to be liquid in an electrical line, and there was no other fuel or liquid trail on the head, it looked like the GP was leaking outward from the head.

I replaced the Made in Germany-labelled braided lines with Viton.

But - changing the aged hardened lines was a hassle. The base of the hoses was no longer anything resembling flexible rubber - more like hard plastic.

I could not pull them off since the base of the old lines had hardened into an inflexible shape over the barb. I pulled straight up and the line broke. I could swivel it, but not remove it. I tried a razor blade but that created too much fuzz near an open fuel line for my comfort level. I used a small screwdriver and pushed by hand in a chisel-like fashion to crack the base of the return line and split the end to remove it.

Hopefully I was pushing low enough on the fitting that I did not nick the barb. I only pushed/scraped on the line until I felt a little "give" then bent the line and created a split on the end.

Jeremy5848 · #7 09-04-2009, 08:03 PM

Quote:

Originally Posted by Yak

. . . Hopefully I was pushing low enough on the fitting that I did not nick the barb. I only pushed/scraped on the line until I felt a little "give" then bent the line and created a split on the end.

Well done. Nicking the barb is a no-no.