I bought my 1992 500SEL a couple of months ago. After smelling coolant in the garage, I decided to put it up on the hoist and have a look. There must have been 20 leaks! All hoses in need of tightening. No worries, a very cheap fix.
I drove it about 1000 miles and observed no loss of fluid. One morning I smelled coolant as I was getting out of the car. Dang! Now what? So I topped it off and watched it close. More smells! Each time I checked it, the system was down about a half pint. I was getting over sensitive to the issue as I could observe no leaks.
Then one day I observed coolant on the floor of the garage. Right in front of the passenger side front wheel. Off to the garage I go. After inspecting the car, we noted a tank under fender below the headlamp. No leaking hoses, only a inlet hose running to the pressure cap. The tank was full. So we removed it to inspect.
The mechanic and I both looked at this while scratching our heads and pondered what the heck this tank was all about. Nothing in the owners manual. A review of the AllData didn't really describe what the heck we were looking at.
Our conclusion is that this is an overflow tank. We emptied it to about 1/3 capacity and put it back together. It appears the owner (that would be me) was over filling the system due to his hyper-sensitive inspection of the coolant tank.
So what is the proper procedure on this? I note the spill-over outlet just dumps into the wheel well area, but it was also dribbling all over the place making one very smelly mess. And how are you supposed to empty this tank? A siphen hose?
Any expert advice on this would be appreciated. I feel fortunate to have a neighborhood mechanic that will endulge me with his help--a genuine MB dealer is 100 miles away. Today's education only cost me an hour and $32 of Stupid Tax.
The tank would be the windshield washer fluid tank. You should see the washer fluid pump attached on the lower right side of the tank. The W140 has a coolant hose running to the tank with the coolant running through a coil of metal tubing inside to warm the fluid to prevent freezing (or to melt the fluid if it has already frozen upon standing).
Item S in this image from alldatadiy.com
Brett
Last edited by Brett San Diego : 12-06-2007 at 09:29 AM.
Thanks for posting that diagram. The tank in question is pictured as item 1A. The hose runs from the pressure cap on the reservoir down to the tank, which is tucked under the plastic skirt on the inside of the front tire fender well. It sits next to the windshield washer tank.
My question is, should this be emptied? How? And why does it fill in the first place?
Under normal conditions the expansion tank (1) will take care of increased volume of hot coolant. After the radiator cools down the vacuum inside it will suck up the coolant from the expantion tank back to the radiator. Nevertheless, if for some reason coolant gets the boiling point (say, a failed water pump) the overflow tank (1A) should take care of boiling coolant and keep it from being deposited on the ground.That said the overflow tank (1A) should be normally empty and the expansion tank (1) half empty.
Thanks for posting that diagram. The tank in question is pictured as item 1A. The hose runs from the pressure cap on the reservoir down to the tank, which is tucked under the plastic skirt on the inside of the front tire fender well. It sits next to the windshield washer tank.
My question is, should this be emptied? How? And why does it fill in the first place?
Ah, I see. In that case, you most likely have a failed coolant reservoir cap. It is no longer holding pressure. I checked the passages on mine to confirm, and coolant only reaches the overflow tank by passing through the pressure relief in the cap (or around the cap seal). The coolant trip to the overflow is one-way. Under normal conditions, it should be completely empty. The tank is there only to catch abnormal overflow from the cooling system.
There are multiple reasons why the cap may not be holding pressure. 1. The valve built into the cap is defective. 2. The O-ring on the cap that seals against a smooth surface where the cap screws into the coolant reservoir is damaged or missing. 3. The sealing surface in the coolant tank orifice is damaged. For 1 and 2, a new coolant cap should solve the problem. For 3, it would take a new tank, unless you can rectify the damage in some way.
Yes, $32 is cheap. I got lucky. It's one of the joys of living out on the prairies of Minnesota. The local fella has three hoists and an assistant. He's a long way from a MB mechanic. In fact, yesterday he told me this was the first one he's had any intimate experience with. But what the heck. With AllData and a complete set of general tools, you can do a lot. I figure I can give him an education in MBism at his shop rate. And he lets me rummage around underneath the car while it's in the air. Free coffee to boot.
Ah, I see. In that case, you most likely have a failed coolant reservoir cap. It is no longer holding pressure. I checked the passages on mine to confirm, and coolant only reaches the overflow tank by passing through the pressure relief in the cap (or around the cap seal). The coolant trip to the overflow is one-way. Under normal conditions, it should be completely empty. The tank is there only to catch abnormal overflow from the cooling system.
There are multiple reasons why the cap may not be holding pressure. 1. The valve built into the cap is defective. 2. The O-ring on the cap that seals against a smooth surface where the cap screws into the coolant reservoir is damaged or missing. 3. The sealing surface in the coolant tank orifice is damaged. For 1 and 2, a new coolant cap should solve the problem. For 3, it would take a new tank, unless you can rectify the damage in some way.
Brett
I figured it was supposed to be empty but wanted to understand why it filled in the first place. What's really odd is that the engineer that created this car didn't give me an option as to how to empty it. Removing the tank is a real pain. And there is only an inlet hose. The outlet is just a hole in the top of the tank. There is no way to empty it. I guess I'll have to siphon it out.
Linear Mode
