300SDL leaking cooling from expansion tank - PeachParts Mercedes-Benz Forum

ah-kay · #1 06-16-2009, 04:18 PM

I don't know whether it is a serious problem or not. My SDL is leaking/dripping coolant from the expansion tank, the one behind the passenger fender. I have never seen what is behind the fender but it seems to have a drain pipe leading to the wheel well. The car never over heat and it hoovers around 80-85 degree C even it a hot day. I do not need to add coolant as there is no warning light in dash. The car starts first time every times and drives well. No smoke at idle or when running. Is it a serious problem like a blown gasket coming? I overfilled the radiator? Or the radiator cap cover is not to spec?

Any help is appreciated.

TX76513 · #2 06-16-2009, 04:28 PM

Pressure test your cooling system - it could be a simple fix by just replacing your expansion tank cap. Excessive pressure could be more serious - and would be cause to investigate further.

Hit Man X · #3 06-16-2009, 05:05 PM

My 560 was doing this, new tank fixed the issue.

Try the cap as they're cheap, but if you have a YELLOW expansion tank... spend $40 to replace it and a few more for a new cap. Stay with OEM parts, the URO brand is hit/miss for the aftermarket.

Jeremy5848 · #4 06-16-2009, 05:07 PM

First, let's get the terminology straight. The "expansion tank" sits on the passenger inner fender in the engine compartment and has a pressure cap. It is under pressure at operating temps; leaks in it suggest an age-related crack that can be disastrous if you happen to be looking closely when it goes "boom."

However, the tank that is "behind the passenger fender," if that's how you literally mean it, is the "overflow tank," which has no cap and is never under pressure. It acts simply to collect any overflow from the expansion tank and return it when the system cools down. If it is dripping, it may simply be that the piece of hose from the expansion tank to the overflow tank has rotted--that's what happened in my '87 300D Turbo (W124, OM603). I removed the fender liner, took off the tank, cleaned it out, and replaced the hose. Documented it here. Another possibility is that the overflow tank itself has cracked. You may be able to apply some silicone sealer or you may have to replace the tank.

AFAIK, my expansion tank has never gotten full enough to utilize the overflow tank since I have had the car; you may have too much coolant in your system. The coolant is supposed to come up to the joint in the tank, about half full, when cold.

Jeremy

brandlj · #5 06-16-2009, 05:20 PM

I am confused. I have a 86 300sdl and I do not have another expansion tank in the passenger fender. I do have a little leak that always drips over there and it is water from my windshield washer bottle. I have a small leak in the line that goes to my headlight washers at the pump itself and it drips out just behind my passenger front wheel. Could this be what you are seeing?

Jeremy5848 · #6 06-16-2009, 05:34 PM

Quote:

Originally Posted by brandlj

I am confused. I have a 86 300sdl and I do not have another expansion tank in the passenger fender. I do have a little leak that always drips over there and it is water from my windshield washer bottle. I have a small leak in the line that goes to my headlight washers at the pump itself and it drips out just behind my passenger front wheel. Could this be what you are seeing?

EPC shows that the 300SDL (W126.125) has an expansion tank on the right (passenger) inner fender and an overflow tank in the left (driver) fender -- see the attached diagram from EPC. The expansion tank is #89 and the overflow tank is #122.

Nonetheless, you are correct and thanks for mentioning the headlamp washer as a possible leak source. I have removed mine and never think about it any more.

Jeremy

Brian Carlton · #7 06-16-2009, 07:58 PM

Quote:

Originally Posted by Jeremy5848

EPC shows that the 300SDL (W126.125) has an expansion tank on the right (passenger) inner fender and an overflow tank in the left (driver) fender -- see the attached diagram from EPC. The expansion tank is #89 and the overflow tank is #122.

Interesting.

I've never seen an SDL with the overflow tank as pictured.

ah-kay · #8 06-16-2009, 08:05 PM

Good info but I am confused.

I know there is a tank behind the passenger fender and it is leaking/dripping as far as I know. There is a drain pipe goes in the wheel well and I see coolant coming out. Is this the overflow tank and is not pressureized?

There is no leak in the expansion tank. What causes the coolant to go into overflow tank from the expansion tank? Overfilled?

I will take a look at the 'overflow tank' over the weekend.

Brian Carlton · #9 06-16-2009, 08:08 PM

Quote:

Originally Posted by ah-kay

There is no leak in the expansion tank. What causes the coolant to go into overflow tank from the expansion tank? Overfilled?

When the cap releases at the specified pressure, the coolant must go somewhere. If you have an overflow tank..........it goes there.

In my case, it dumps onto the ground in front of the passenger fender.

This should only happen once. On the next startup, the temperature rise should cause the system to just reach the cap setpoint.

The only other time it will occur is if the engine gets significantly hotter than normal.

brandlj · #10 06-16-2009, 09:57 PM

Quote:

Originally Posted by Jeremy5848

EPC shows that the 300SDL (W126.125) has an expansion tank on the right (passenger) inner fender and an overflow tank in the left (driver) fender -- see the attached diagram from EPC. The expansion tank is #89 and the overflow tank is #122.

Nonetheless, you are correct and thanks for mentioning the headlamp washer as a possible leak source. I have removed mine and never think about it any more.

Jeremy

Very Interesting, Tomrrow I want to check and see if I have one. I have never noticed an overflow tank on my 86. I will report after I look around. Thanks for the info

Bio300TDTdriver · #11 06-16-2009, 10:22 PM

Quote:

Originally Posted by Brian Carlton

Interesting.

I've never seen an SDL with the overflow tank as pictured.

Have you ever pulled the wheel well liner and looked? I found mine when I did that. Yes I have a 124 and you are talking about a 126, but since the EPC shows it, I'd bet they all had them when they left Sindelfingen.

Jeremy5848 · #12 06-16-2009, 11:22 PM

Is that green coolant I see in the overflow tank???

Bio300TDTdriver · #13 06-16-2009, 11:36 PM

Quote:

Originally Posted by Jeremy5848

Is that green coolant I see in the overflow tank???

Why yes it is. It was put there by the cracked head. Go figure a #14 head cracked. Luckily, MB planned for the catastrophe by placing a hidden tank to collect the over flowing coolant.

They didn't want me covering I-5 with the icky green coolant.

After the head was replaced I went on a hunt for the tank. I found it and emptied the coolant out. I suspect it is still dry, but I may check it this summer if I get a chance.

Oh, it has the proper coolant in it now. I had the water pump replaced when the head was done. The radiator is a Nissens, so I know that has been replaced and the viscous clutch was changed by me 10 days ago.