Some Very Basic Coolant Change Questions
 

I have never changed my own coolant....but have faithfully had it changed by my tech every couple of years so I'm confident the system is pretty clean. But, this seems like something I should be able to do myself. I've read various threads, but I'm still unclear on a couple of things.

This is for a 1991 and 1992 300D.

1. Of the total system capacity, approximately how much comes out if I ONLY drain the radiator? How much comes out if I drain BOTH the radiator and the block? I ask this because I might opt not to mess with the block drain and simply drain the radiator a bit more frequently. But maybe this is a bad idea?

2. Once the radiator is drained and the plug screwed back in, do I fill it by disconnecting the upper radiator hose and finding some sort of L-shaped or bendable funnel to pour coolant in? I'm assuming I don't add by filling the expansion tank.

3. If I take this simplified approach (i.e. only draining the radiator), is it simply a matter of draining, filling, starting the engine, then burping with expansion cap off? Anything else I need to watch out for, attend to?

Thanks for helping me out as I slowly but surely add to the number of things I'm able to do on my own!

you get about 1/3 of the coolant out by draining the radiator. and all the sediment remains in the block. not recommended. best is to pull the block drain, and flush with a hose the radiator, block, and heater core. 2nd choice would be to drain the radiator, put a flush kit into the heater hose, and flush with a garden hose the block and heater core...
just draining the radiator is not really a good idea.

as to filling it. the 602/03 block has a nice vent right in the top of the head, and it balances the fluid, so you can fill with just pouring into the expansion tank! go slowly, and don't fill above the small return hose, so air can escape easily.

So, even though the radiator at that point is empty, I can start the engine and the system will suck coolant into the radiator from the expansion tank?

nooooo.
don't start the car until all burping of the radiator/block is finished! make sure you have coolant exiting the vent line!
the expansion tank is connected to the bottom of the radiator with a 1" line, and to the top of the block with a 1/4" line. so air is pushed out of the block perfectly. just make sure you get coolant there.

I got a great tip today, regarding coolant change!
 

First, you definitely want to drain both the radiator (drain plug at bottom of radiator), and the engine block (drain plug-19 mm-on side of block forward of block heater...reach in with long extension bar. This will completely drain coolant (except for little in the heater core).

The great tip was this: To refill the coolant (after plugs are re-installed!), first disconnect the end of the large radiator/coolant hose at the top of the radiator, and fill as much 50/50 mix as it will take by pouring into the hose. Note that this allows you to fill engine block "behind" thermostat. Then reconnect the hose, and then fill as much as you can into the radiator by pouring into the expansion tank...this fills in "front" of the thermostat.

By doing this, you get coolant into the system on both sides of the thermostat, so you don't have the big air pocket, and the problem with running the car to over heating in order to get the thermostat to "release" and allow coolant to circulate.

I got this tip from an indy mercedes repair shop I happened upon while on the road today...I stopped to buy coolant, and we got to talking, etc....

yes, this method is very important on the 617 N/A motors, and pretty important on the turbo versions, but not needed on the 601/2/3 equipped vehicles. slowly filling the radiator through the expansion tank, then SLOWLY filling the radiator until coolant spills out the bleed hose will fill the block perfectly. it's best if you park the car with the radiator higher than the block, park the nose of the car uphill, and it'll be faster, but it'll fill fine if you go slow.

On my 602.96 I removed the bottom radiator hose from the radiator and collected all the coolant in a bucket. Then I drained the block by removing the block plug over near the turbo. Then, after disconnecting the top hose, I took my garden hose and flushed the radiator and as much of the block as I could. Also used the garden hose to flush out the resovoir at the same time. Once all that fresh watrer stopped dripping I buttoned it all back together, added 1 gallon of Zerex G-05 (gives me a 40% mix) and the rest water. My 602 vents air pockets to the reservoir so I kept an eye on it for a 100 mile or so.

bumping this up to the top, for the member.
can anybody post a link to a pictorial or similar to assist him in the change?
thanks.

This is probably the single most important thing to do !!

Once you have filled it & started it & checked for leaks, take it for a run around the block (a mile or so) & check for leaks & the level of the coolant.
Then after you drive the car for a regular short run, check it again.
When you next fill with fuel, check it again.
If at any point in the not to distant future, the temp goes up unexpectedly or the motor gives other signs of being hot, check the coolant level & for leaks.
Its important to make sure that you have the heater operating when the car is first started to make sure it is filled with coolant.

And I'd say that forgetting about the heater is probably the most common error resulting in "I've just changed my coolant and I now think my cooling system is leaking because the coolant level is too low" threads...

Where EXACTLY on the 602 is the block drain?

I assume to do this I need ramps for front?

This works fine on pretty much any MB engine, and will speed the fill process. Otherwise you have to fill slowly, with liquid getting to the top of the reservoir neck, to get liquid to flow through the vent line to the block. It's slow and painful. DO NOT start the car until you can feel liquid present in the upper radiator hose when you squeeze it! Turning the heater to "max" temp will turn on the auxiliary coolant pump, which will help circulate coolant through the heater core, even with the engine off (key must be on).

Here is the factory procedure - the location of the OM60x block drain is shown on the last page:
http://w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Maintenance/My81/2080.pdf

Ideally, you should drain block & radiator with a cold engine, then with the upper radiator hose and heater core inlet hose (near brake booster) disconnected, insert a garden hose (on low/medium flow) run through the radiator, block, and heater core with all drains open. This will flush ~99% of the old stuff out. Remove hose, wait for the water to stop flowing out the drains, then close everything up and re-fill with your preferred percentage of MB antifreesze or Zerex G-05. If you measured what drained out, you should be able to get that same amount (or within 1 quart of that amount) back in before re-starting the engine. Top off as needed after a test drive with heater running; best to wait until the next morning so you're adding to a cold engine. Watch the level for the next few days until it, uh, levels out.


:1eye:

Dave, is it bad to drain a hot engine block?

I'm not sure that it's the draining that's the issue, but the filling part with cold coolant may be a "shock" to the warm components. :cool: