Does Coolant Circulate through Expansion Tank? - PeachParts Mercedes-Benz Forum

shertex · #1 10-03-2022, 09:52 AM

My understanding is that it does but wanted to confirm. Wanted to test my coolant and it's a lot easier to take the sample from the expansion tank.

Zulfiqar · #2 10-03-2022, 10:06 AM

Quote:

Originally Posted by shertex

My understanding is that it does but wanted to confirm. Wanted to test my coolant and it's a lot easier to take the sample from the expansion tank.

It has very low circulation compared to whats in the engine, its more of a degas tank to keep liquid level at the highest point in the system.

87tdwagen · #3 10-03-2022, 10:10 AM

Typically not much flow through the expansion tank. Most cooling systems, the return feed to the expansion tank is for overflow under extreme heat, or a little expansion/contraction in the system during cool down, but really not enough to move a lot of volume under normal conditions. If sampling, IMHO, you would be better off capturing from the radiator drain.

Sugar Bear · #4 10-03-2022, 10:47 AM

Technically I'd say no circulation, just a rise and fall of the level which can cause minute mixing.

dieselbenz1 · #5 10-03-2022, 11:19 AM

While you are at it may be interesting if you measured the milivolts. Black lead on ground red probe in resoviour .4 milvolt or less it's good.

ah-kay · #6 10-03-2022, 11:24 AM

The coolant will be "circulated" by convection. Heat rising from hot to cold will mix your coolant. If you are a purist then take the sample from the top radiator hose.

tangofox007 · #7 10-03-2022, 11:25 AM

Quote:

Originally Posted by shertex

Wanted to test my coolant and it's a lot easier to take the sample from the expansion tank.

No problem with that unless you just recently added coolant or water.

EDBSO · #8 11-07-2022, 10:02 PM

After a few heat cycles it will be mixed and the same as in the block.

As preventative maintenance I drain the expansion tank and refill with 50/50 Zerex G48.

In my mind I am simply refreshing the additive package a bit a couple times a year spring & fall. I do about a quart at a time which is about 8% of the capacity. Been doing it for years and the fluid looks like new.

I started doing this after I met a fleet manager who did this on all vehicles in the fleet.t

shertex · #9 11-08-2022, 05:58 AM

Quote:

Originally Posted by EDBSO

After a few heat cycles it will be mixed and the same as in the block.

As preventative maintenance I drain the expansion tank and refill with 50/50 Zerex G48.

In my mind I am simply refreshing the additive package a bit a couple times a year spring & fall. I do about a quart at a time which is about 8% of the capacity. Been doing it for years and the fluid looks like new.

I started doing this after I met a fleet manager who did this on all vehicles in the fleet.t

How does adding coolant affect the additive package?

JHZR2 · #10 11-08-2022, 09:02 PM

My 602 definitely curvulates a bit through the tank. It’s not as obvious on the others.

INSIDIOUS · #11 11-09-2022, 11:19 PM

Quote:

Originally Posted by JHZR2

My 602 definitely curvulates a bit through the tank. It’s not as obvious on the others.

curvulates. dang. you made we look that up. and NOW you NEED a spankin

JHZR2 · #12 11-10-2022, 08:11 AM

Quote:

Originally Posted by INSIDIOUS

curvulates. dang. you made we look that up. and NOW you NEED a spankin

Ha! Fat fingers on the iphone made a real-ish word!!

Not intentional…

EDBSO · #13 11-16-2022, 02:03 PM

Quote:

Originally Posted by shertex

How does adding coolant affect the additive package?

You are removing old (depleted) coolant and adding "fresh" coolant with fresh additives (lubricants and anti-corrosion) Rather than a full drain and refill you are doing a partial drain and refill.

BillGrissom · #14 11-23-2022, 11:17 AM

The coolant reservoir is effectively an extension of the radiator since it runs at the same pressure and has an upper and lower hose. Most Euro cars may be like that. There should be circulation due to temperature differences and pressure difference across the radiator core. Different than U.S. cars where the reservoir is an unpressurized overflow bottle.

In U.S. cars, the radiator can suck coolant back from the reservoir once it cools. Not sure how that works but probably has to do with the 2 rubber gaskets and perhaps a thermostat-like device in the cap.

JHZR2 · #15 11-23-2022, 11:24 AM

Quote:

Originally Posted by BillGrissom

The coolant reservoir is effectively an extension of the radiator since it runs at the same pressure and has an upper and lower hose. Most Euro cars may be like that. There should be circulation due to temperature differences and pressure difference across the radiator core. Different than U.S. cars where the reservoir is an unpressurized overflow bottle.

In U.S. cars, the radiator can suck coolant back from the reservoir once it cools. Not sure how that works but probably has to do with the 2 rubber gaskets and perhaps a thermostat-like device in the cap.

Agreed relative to pressure and the system all being one condition.

IME, burping air and getting circulation, it’s easy on the w123s, regardless of if filled in the pressurized reservoir like the 617, or at the radiator like the 616. However, for the 602 vs 603 (w126), it’s vastly different. My w124 602 has a second line going to the reservoir, and is super easy to get all air out. My w126 603 has to be burped very carefully or else it will not be full, and the temp sensor will register an overheat very rapidly. It isn’t really happening (well, at least if you just idle or drive gently), but it’s annoying how much more water it takes.