87 300SDL fuel leak, what is this?

[julio.garcia.fc]

For a while, I have been chasing a fuel leak with little luck. MB wanted to replace my IP for a cool $3500. Today, I replaced a couple of fuel lines, which looked about as old as the car. They were wet and I thought one of these two was possibly cracked. After I started to tighten the hose that comes from the plastic pre-filter, I noticed that the plastic connector on the other side was leaking when I wiggled it. It looks like a plastic cylinder inside the aluminum cylinder has a bad seal.

I have no idea what the part is called or the number for it. I am hoping someone here might know. Please see the attached pictures. Looks messy to replace. There was a fair bit of fuel that leaked just from changing the two hoses in the area that I replaced The one from the left of the cylinder to the pre-filter and the one on top of the cylinder). Would this be better done by someone else or, other than the mess, is it simple enough to be done by a novice like me. Here are the images.





Thanks in advance for any suggestions.

[julio.garcia.fc]

FYI, I got this private reply :

That part which is leaking on your car is the Fuel Preheater Thermostatic Valve. Depending on the ambient temperature it will route the fuel coming from the tank thru the preheater that wraps around the rear of the oil filter cannister and is attached to the coolant line coming from the cylinder head.

When it is cold enough the wax capsule inside the thermostatic valve opens the valve to the preheater, when it's warmer the wax capsule prevents the valve from doing that.

The fix is to clamp off the fuel lines, remove the thermo valve, remove the C-clip that holds the palstic inlet piece in place, remove the plastic inlet piece and replace the seal behind it. The seal costs a couple dollars and a new plastic inlet piece costs a couple dollars if you need one of those. Replace those parts put it back together and reinstall it. Check both the motor mount and the engine shock mounts if it has been leaking for very long as they will deteriorate from contact with diesel fuel, good luck!

P.S. My engine shock mounts will need to be replaced after I fix this. I have not noticed my motor mounts being bad but I will inspect again.

The "clamp the fuel lines" tip was awesome (Duh!!!). The clamp will be much less unhappy than my wife holding her index finger on the end of the lines.

[julio.garcia.fc]

Found additional information here: Please help, Fuel Leak maybe fuel pre-heater - Benzworld.org - Mercedes-Benz Discussion Forum

and here:

OM601, 602. 603 Diesel fuel thermostat REBUILD parts list

http://www.peachparts.com/shopforum/attachments/diesel-discussion/53799d1207005905-92-300d-leaking-fuel-pre-heater-om60x-fuel-preheater-function.jpg

Here is where to get the part:

Mercedes-Benz 300SDL Genuine Diesel Fuel Thermostat W0133-1603611 at Auto Parts Network

[Brian Carlton]

Originally Posted by julio.garcia.fc

FYI, I got this private reply :

That part which is leaking on your car is the Fuel Preheater Thermostatic Valve. Depending on the ambient temperature it will route the fuel coming from the tank thru the preheater that wraps around the rear of the oil filter cannister and is attached to the coolant line coming from the cylinder head.

When it is cold enough the wax capsule inside the thermostatic valve opens the valve to the preheater, when it's warmer the wax capsule prevents the valve from doing that.

The fix is to clamp off the fuel lines, remove the thermo valve, remove the C-clip that holds the palstic inlet piece in place, remove the plastic inlet piece and replace the seal behind it. The seal costs a couple dollars and a new plastic inlet piece costs a couple dollars if you need one of those. Replace those parts put it back together and reinstall it. Check both the motor mount and the engine shock mounts if it has been leaking for very long as they will deteriorate from contact with diesel fuel, good luck!

P.S. My engine shock mounts will need to be replaced after I fix this. I have not noticed my motor mounts being bad but I will inspect again.

The "clamp the fuel lines" tip was awesome (Duh!!!). The clamp will be much less unhappy than my wife holding her index finger on the end of the lines.

Please give Phil your most heartfelt thanks.

He knows more about this engine than anyone on the board.

Yes, I know his screen name will not be "Phil".

[julio.garcia.fc]

Originally Posted by Brian Carlton

Please give Phil your most heartfelt thanks.

He knows more about this engine than anyone on the board.

Yes, I know his screen name will not be "Phil".

I did and I am very thankful that anyone would bother with a complete newbie like myself. But, I am learning.

[ehm]

Could someone give me the part number or specs for that fuel line going to the part the gentleman is pointing to in the picture above; mine has fuel bleeding through it. Thanks!!!

[bigpanda16]

A lot of people swear by mm sized hoses. But on the feed and return Line on om601/2/3, I have used 5/16” fuel hose with no problem

[ehm]

Many thanks; are there any specifications I need to seek out given that it is so close to the engine? For instance I found one hose in my rudimentary inventory that said not for under hood use.

[ehm]

And that hose going to that preheater thermostatic valve is only 5/16? Looks bigger than that to me...

[Diseasel300]

Fuel line on these cars is 7.5mm ID. If you use 5/16, it'll "work" but you WILL have air ingress issues. It doesn't matter how tight you wrench down on the clamps. Source the correct hose, it'll save lots of headaches later down the road.

[ehm]

I appreciate the input!

[dieselbenz1]

Originally Posted by Diseasel300

Fuel line on these cars is 7.5mm ID. If you use 5/16, it'll "work" but you WILL have air ingress issues. It doesn't matter how tight you wrench down on the clamps. Source the correct hose, it'll save lots of headaches later down the road.

X2 when I used 5/16 life was great. A year and a half later air issues.