Coolant Level Drop: Thoughts, Concerns? - Page 2 - PeachParts Mercedes-Benz Forum

vstech · #16 09-27-2010, 09:26 PM

yup two fold issues, if your overflow hose is worn, you can be dumping coolant into the overflow, but not siphoning it back into the radiator when it cools. the other side of the equation is your cap could be weak or cracked where you can't see it, allowing too low a pressure causing boiling in the block and expelling of coolant out the seeping hose.

for giggles, put a new 20# cap on the tank, then replace the hose that goes to the overflow tank in your fenderwell, NOT THE PRESSURE TANK HOSE. see if your disappearing coolant returns.

shertex · #17 09-28-2010, 07:10 AM

Quote:

Originally Posted by babymog

The black hose leading from the top of the expansion tank, into the fender, to the recovery tank (located behind the RF fender liner inside the fender) is a known leaker at this age, especially on southern cars. You will not be able to keep the expansion tank full but it will not empty if this or the recovery tank is the problem.

Can you explain a bit more as to how the recovery tank works? I'm guessing that the path between expansion tank and recovery tank is two-way....that it's designed to send coolant back to the expansion tank under certain conditions....that it somehow serves to buffer the amount of coolant in the rest of the system?

This is the first I knew of its existence....just trying to learn whatever I can.

Thank you.

Blevinsax · #18 09-28-2010, 08:03 AM

Long time no see everyone...

Yesterday as I drove my '91 350SD home, it suddenly began to heat up - not into the red, but pretty far north on the gauge. I stopped the car in the garage and saw the coolant expansion tank (the one by the air filter, right?) was empty and the cap was ajar. I had just added a little water to it the day before as it has a slow leak somewhere - did I perhaps not put the cap back properly? I added water (no coolant on hand) and it cooled down and seemed to be okay. What should I be watching for at this point?

Thanks to all for your help!

shertex · #19 09-28-2010, 08:13 AM

Quote:

Originally Posted by shertex

Can you explain a bit more as to how the recovery tank works? I'm guessing that the path between expansion tank and recovery tank is two-way....that it's designed to send coolant back to the expansion tank under certain conditions....that it somehow serves to buffer the amount of coolant in the rest of the system?

This is the first I knew of its existence....just trying to learn whatever I can.

Thank you.

In the meantime, read this in the FSM:

"The overflow reservoir protects the engine from loss of coolant at high ambient temperatures. At high ambient temperatures, fuel may flow out at the overflow line after the engine is switched off. The overflow reservoir collects this fuel which flows out. Once the engine and the coolant have cooled down, a vacuum exists in the cooling system which transports the coolant back out of the overflow reservoir into the expansion reservoir."

From http://www.w124performance.com/service/w124CD1/Program/Engine/602_603/20-0001a.pdf (even though only 603 is referenced here, elsewhere in the manual it confirms that 602 has overflow reservoir)

So that answers my question but raises another. If fuel flows out through this line, won't it also get sucked back in...into the cooling system?? I'm sure I must be missing something. Is this a miss print, or do they really mean FUEL?

Thanks.

vstech · #20 09-28-2010, 08:47 AM

that's gotta be a misprint.
they meant coolant.

babymog · #21 09-28-2010, 11:33 AM

If the overflow line (the one between the expansion tank and the overflow tank) has a leak, it will pass fluid into the overflow tank (in the fender), but will only suck air back in through the leak. Often hard to find any dripped water as it runs down the inner fender and tends to disappear.

compress ignite · #22 09-28-2010, 01:41 PM

Blevinsax,

You should be looking for a way that "Unauthorized Beings" got under your hood and left the Cap Loose.

I'd just keep an eye on it.(The Temp Gauge)

Blevinsax · #23 09-29-2010, 11:16 AM

So, it seems like I left the cap ajar - dumb me. The car ran perfectly yesterday, so I guess that means I simply didn't secure the cap properly when I put it back on after topping off the coolant...

That's certainly better than uncovering some more costly problem!

shertex · #24 10-08-2010, 07:44 AM

Quote:

Originally Posted by babymog

If the overflow line (the one between the expansion tank and the overflow tank) has a leak, it will pass fluid into the overflow tank (in the fender), but will only suck air back in through the leak. Often hard to find any dripped water as it runs down the inner fender and tends to disappear.

Let's assume I have a leaking overflow line. Once the coolant in the expansion tank drops to a certain level low enough where there would be no overflow, would I at that point stop losing coolant? (no overflow, therefore nothing to be sucked back in?)

babymog · #25 10-08-2010, 10:10 AM

Presumably so, yes.

vstech · #26 10-08-2010, 11:13 AM

it should stop, but you could be boiling coolant, and the steam would continue to exit.

JHZR2 · #27 10-08-2010, 03:58 PM

I would do a used oil analysis just to be sure.

shertex · #28 11-11-2010, 04:45 PM

AN UPDATE: once the coolant level when cold dropped to the seam line in the expansion tank, it stopped dropping. I've driven 800 miles without a noticeable drop in level (before that, it dropped 1/2" over the course of 700 miles). So that sounds like very good news, correct? From what I read from the other posts, it seems like my problem must be that the expansion tank is not sucking back overflow coolant from the overflow tank (presumably due to a leak in the hose).

charmalu · #29 11-11-2010, 11:44 PM

Quote:

Originally Posted by shertex

AN UPDATE: once the coolant level when cold dropped to the seam line in the expansion tank, it stopped dropping. I've driven 800 miles without a noticeable drop in level (before that, it dropped 1/2" over the course of 700 miles). So that sounds like very good news, correct? From what I read from the other posts, it seems like my problem must be that the expansion tank is not sucking back overflow coolant from the overflow tank (presumably due to a leak in the hose).

The hose from the expansion tank to the Overflow tank is like a straw.
The next time you have a Coke or Milkshake, poke a hole in the straw. now try sucking on it. If you are sucking air through the hole, it will be harder to get the fluid to come up the straw.

The overflow hose workes the same way.

Charlie

punkinfair · #30 11-11-2010, 11:55 PM

i had a similar issue with my '87 TD. the overflow tank had a very small crack in it and the fluid was leaking out. it would only leak when the engine was hot and when it leaked the amount of the leak was very small, so that the liquid never made it to the ground, it evaporated or dried up before making it to the ground. perhaps a small amount made it all the way down to the ground but i never noticed it, like there was never even a small puddle. the fluid leaked in a way that you could not see any fluid on the bodywork of the engine bay, it was hidden from easy view. once the fluid level fell below the level of the crack, the leak would stop, that was the other mystery. the only way i discovered the crack was by removing the overflow reservoir and looking at the underside of it. i was almost sure there was something wrong with the engine internally because it seemed to be the only explanation for the behavior. i ordered the oil analysis kit and everything. luckily i was dead wrong and a new reservoir was all the was needed.