Cooling System Cleaning - Mercedes-Benz Forum
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post #1 of 38 (permalink) Old 06-18-2014, 07:49 PM Thread Starter
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Cooling System Cleaning

It is time to flush out my cooling system; had an indie do it for me 2 years ago - or so I thought. This is a first for me so I researched it here on the forum, and used the procedures in the maintenance manual (20-010). The cooling system has not performed well in central New Mexico so I planned a de-oiling and de-scaling (20-015).

I drained the radiator first - green coolant with lots of contaminant in it. When I opened the block drains, nothing happened. I pulled both block drains and found hardened crud in the passages. I used a pick and small wire pipe brush to clean it out and drain the block. Clearly, I have coolant passage problems.

I made a degrease solution and ran the car for about 20' with that in there - I will flush it out and repeat tomorrow. The Citric Acid treatment will follow.

The last picture is a pick stuck in the gunk clogging my block drain.
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post #2 of 38 (permalink) Old 06-18-2014, 08:07 PM
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I don't think de-oiling is going to fix this problem.

The citric acid flush might after a bunch of flushes and re-dos. Unfortunately anything that un-cruds might get lodged in your rad or somewheres else.

When is the last time the rad went to a rad shop for a good going over?
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post #3 of 38 (permalink) Old 06-18-2014, 10:18 PM Thread Starter
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This indie that I spoke of rebuilt my A/C system. When he was done, he found that the car ran really hot with the A/C running. He pulled the radiator and sent it off for a boil out and whatever else they do. I'll spare you the trauma that I went though in 3 months getting an A/C system rebuilt - bottom line; never going back, doing my own work.

I agree with the necessity of a citric acid flush. The main reason I'm doing the de-oiling is because 20-015 says do it before you to the acid. Apparently, this enables the chemistry to work better.

I did not order enough citric acid. The maintenance manual calls for a 10% solution which amounts to 1.5KG for the M117. I bought a single jar - 500g. I'm going to visit this crazy Iranian pharmacist tomorrow. If he doesn't have citric acid, I'll go back to MB of ABQ and wait 3 days.
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post #4 of 38 (permalink) Old 06-19-2014, 04:00 AM
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Originally Posted by cushjbc View Post
I did not order enough citric acid. The maintenance manual calls for a 10% solution which amounts to 1.5KG for the M117. I bought a single jar - 500g. I'm going to visit this crazy Iranian pharmacist tomorrow. If he doesn't have citric acid, I'll go back to MB of ABQ and wait 3 days.
Try your local WallyWorld, the one by me stocks Ball brand (the canning people)
citric acid. One of our local brew houses also stocks it, but that
usually ends up costing me more

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post #5 of 38 (permalink) Old 06-19-2014, 04:25 AM
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I bought a 5 kg bag on eBay for 10$.

What I did on my OM617 and OM603 was to make a block flusher out of galvanized pipe connected to a valve connected to about 6feet of hose. I screwed the pipe into the block drain connected the hose to the garden hose and ran water through the engine and out the lower radiator hose which I disconnected from the radiator. When the gunk stopped coming out, I hooked up the radiator hose, filled the system from the block, then shit the valve on the pipe. I added the citric acid and ran the engine for a half hour. I opened the valve and drained the acid, hooked the drain hose back to the garden hose and reverse flushed for 15 minutes with the engine running. I repeated this twice. On our V8s with two drains I would use two pipe-valve set is a picture of the dingus...
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post #6 of 38 (permalink) Old 06-20-2014, 06:06 PM Thread Starter
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I struck out finding local sources for citric acid monohydrate - ordered 2 more jars of MB citric acid. In the meantime, I de-oiled twice and did a flush. I bought a generic flush kit years ago - opened it today and put it to good use.

When I looked at the coolant circuit of the M117, I found a convenient place to introduce fresh water was at the heater faucet. The fitting is 20mm which is very close to 3/4". I bought a 6' length of 3/4" ID heater hose from Autozone. I used a 3/4" T fitting with a check valve, opened the heater faucet (full heat), and removed the radiator drain plug. I ran one hose to the check valve and another hose to the coolant reservoir. I started the engine and let it run for about 10' until the water was clear and suds free.

Next step is another drain procedure followed by the citric acid.
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post #7 of 38 (permalink) Old 06-30-2014, 10:15 PM Thread Starter
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I finished this project today. Used 1.5KG of citric acid from MB (pictured above) because I could not find a cheaper substitute in ABQ. I followed the instructions in article 20-015 by de-oiling the cooling system 3 times then flushing until I had nothing but clear water flowing from the radiator and block drains.

The descaling operation is pretty straight forward. I drained the cooling system (4th time), flushed the system until clear since my car sat for a week. I removed the alternator to gain easy access to the thermostat housing, removed 3 x 10mm bolts to remove the thermostat, then replaced the housing and the old thermostat seal for the descaling step. I used a 5 liter medical tub to mix the solution. The MB stuff is dry white crystals that dissolve easily. I slowly poured this solution into the coolant reservoir. The first 10 liters went in easily, I had to run the engine and burp the system to get the last 5 liters in.

I had a slow leak at the thermostat housing because the seal is not as effective without the shape of the thermostat supporting it inside. If I were going to do this again, I would drill out the old thermostat and use the thermostat frame to make a better seal. This small leak I had makes for a real mess when you do the engine run.

I was amazed when I drained this solution. The fluid that came out was a sticky green Kool-Aid looking stuff that had white grit in it. It took several flushes to get a clear flow again. I think the citric acid is effective at getting congealed coolant from recessed areas; I think the grit must have been hard water deposits and maybe some rusty film. When I put the new thermostat in, The water pump intake and thermostat housing were hospital clean.

In the end, I filled the cooling system with 5 liters of Zerex and 10 liters of distilled water. I am remiss in not using a camera today - I know the rules. I struggled with the mess and a very hot day in Albuquerque and decided not to pause for pictures.
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post #8 of 38 (permalink) Old 07-01-2014, 06:08 PM
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Hi Brad,

I just caught this thread. I'm not sure if you remember me mentioning this when we caught up last - but the removal of the radiator and thermostat is necessary to really get it to work well. The problem is, how do you keep circulating the solution for the minimum 15 minutes??? And you really need to do it for an hour or more if it is possible, when things look bleak.

well I don't know if you have a 20 gallon drum, or even if you have a spare 5 gallon drum laying around, but I found them invaluable for things like this.

My family has a few plumbers so for me some things are easy to do / get hold of.

1. 5 gallon drum - large paint tin works.... as you can take the lid off and see all the junk...
2. some 2" or 1 " copper tube. (about 1 foot length cut into 4 pc.)
3. holesaw
4.brazing torch.
5. 2" rubber hose - or old radiator hoses
6. small stepladder to sit the drum on in front of the car while it's running.

the citric acid you grab from a home-brew place. citric is used to clean out carboys for brewing..... save $$$ and buy bulk.

cut a 2" dia hole (or whatever the diameter of your copper / pipe) in the drum at height, and another at height . braze in 2 pieces of the 4 pc of copper into these holes. It helps if you angle the inlet pipe at the top to create a vortex with the inlet flow. make sure the outlet is at 90 though, (inlet at top, outlet is bottom) like a swirl pot - which is essentially what we are making - on a large scale.
Grab your old rad hoses or if you're flush, some irrigation pipe or other material to join the top and bottom hoses to the drum, using the other 2 pieces of copper and some matching hose clamps.
If your rad hoses are smaller, use smaller pipe if need be. so long as it can form a cooling system loop it doesn't matter how you achieve it. All you're looking for is a substitute radiator.... which is what the 5 gallon drum /paint tin is.
Once it's all hooked up, sit the drum on a ladder to elevate it above the thermostat housing & header tank height.... hence small stepladder or barstool.... remember it's going to get HOT, so don't put it on something that will melt.

Fill the drum up past the inlet pipe. Add the citric acid (about 3-5KG) stir it around until it dissolves and start the car. let the car warm up. At this stage, do not give it any revs. all you want is coolant circulation and no air pockets.
The car will warm up, it will take time as there is more coolant circulating in the system.
You can leave it for an hour or so, and it will be fine. while the coolant is circulating, you will notice some bits of rusty crud falling to the bottom of the drum. This is why you want that outlet higher up on the side, so you don't pick up that crud and recirculate it. You can put a stocking over the bottom pipe stub before you fir the hose to it, to act as a further filter.

Once you are happy with the flush - (bear in mind you can drain and repeat it until the coolant is clear, within reason), you must thoroughly rinse flush the system. best way to do this is with a garden hose, straight into the bottom hose inlet, and car off. let it run on a medium flow for about 15 minutes, which is what it will take to thoroughly neutralize the acid.

That's part 1.

Part 2 is more sensitive. It's about the radiator core.

If you have a brass tank / copper core, then you need to be careful when acid cleaning. If you have an alloy core plastic tank, then you need to worry a fraction less, but you do need a different solution to clean each one.
for copper tank you can use zinc chloride - aka soldering fluid. buy off the shelf or make your own with some zinc and muriatic acid. either way - whatever is cheapest and easiest.
fill the core with a diluted solution, soak for a minute, drain, rinse with water, repeat.

If this is not working, then you can use a slightly higher concentrate, but beware.... an old core is an unknown, and any acid wash or dip can pinhole cores - particularly old ones which have seen many years of internally corrosive fluids.
This will ensure that any passages that are not blocked, will flow cleanly. It does not guarantee that any cores which are badly blocked, will be unblocked. Chemical treatments can only go so far.

The copper / brass radiators are usually soldered with a low-temp solder, and it's easy to take the radiator to a specialist rad guy, to desolder the tank and wire through the cores as well as acid dip, resolder and respray. This will get you some extended life and is a better alternative...HOWEVER -

If the core is 10 years old or more, do yourself a favour and have the rad re-cored.
The overheating issue I had was difficult to diagnose. ended up replacing every part of the cooling system, pumps, tanks, hoses, visco coupling... t-stats etc... (but the rad was flowing heaps, and i mean heaps. the fire hose in my work basement proved this) All except the radiator. Why? because the FIRST thing I did was citric flush and pull the rad and flushed that several times, and it looked like it was absolutely perfectly serviceable.
I finally took the rad to get recored as the last straw. - i'd done the acid clean, everything....

So I had my SLC recored by a specialist guy who does serious earthmoving equipment.
He pulled the tanks off, found the core to be 80% blocked (yet I'd already proved it was flowing huge amounts of water - it just goes to show that your heat-soak issues can be mis-diagnosed when you think the radiator is flowing fine..... when in fact it isnt!)

Specialist guy says "no wonder - your core is not right - it's for a stationary diesel engine" He looks up his catalogue, finds 3 different core applying to Mercedes 350/450/500....

1st core is 3 row parallel (factory), 2nd is a replacement modern 3 row offset, 3rd is a 4 row parallel (factory). He checks the specs of each.

The more modern design 3 row offset core has an 80% efficiency increase over the exact replacement 4 core (4 row parallel which was in the car).

not only that, air flow requirement was less than the 4 core.

Dimensionally the radiator can obviously only use a core that fits within the tank dimensions, otherwise youre talking custom...

After he showed me the old core I was amazed at the blockage - in every single tube! some bad, some completely blocked, some simply hanging in there... it was a tragedy waiting to happen.
He silver brazed the tanks onto the new 3 row offset core and repaired the air bleed line in the header tank, I refitted it to the car.
1st start and it got up to temp quite quickly. I started to get a bit worried I had bigger problems...

But the temp of the car stayed right on thermostat opening temp and never budged - It remained that way over an EVIL summer where we had 45C temps for days on end. I thrashed the car and it did not even look like breaking a sweat.
It sat just over 85 and fluctuated the tiniest of amounts. I was rapt.

and to top that off, we discovered a tag on the original radiator core - it was from 1975... so that told me 3 years after purchase, the SLC's radiator was replaced..... STRANGE!! I wonder what caused that.... but not bad for a 42 year old car eh? It was looked after, but you can't predict these things.

So moral of the story is, citric acid flush will only do so much, but you really need to get the radiator checked as well, especially if it's a bit old... And even if the core looks like it flows plenty - silicone worms and other crap can block the cores and cause big trouble. So while it may work for a while, pay attention to the way the temperature behaves when you're not doing highway speeds.

So I learned something valuable about older Mercedes copper radiators... they can hold huge pressure, and they will work perfectly fine, until the heat-soak threshold is reached. They are far more capable of coping with bad cooling systems than any other car I have owned to date....
But it can catch you out - It doesn't have to happen on a hot day... in fact for me it happened on a cool night on the way home from work, well after peak hour traffic...

Once it happens, you simply cannot cool the system down as the heat input is exponentially greater than the heat loss across the core. This is why cars overheat when seemingly 'unloaded' with regards to engine use.
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post #9 of 38 (permalink) Old 07-02-2014, 05:27 AM Thread Starter
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Thank you for a very informative post - I pulled an entire radiator assembly from a '72 350 SLC in November to keep as a spare. It has the same part numbers as the radiator installed on my car [A 107 501 09 01]. My installed radiator was pulled and flow checked by a reputable radiator shop 3 years ago but I did not get details about rows and offsets. You've got me motivated to take my spare to the radiator guy - have him evaluate the condition and build specs, repair if necessary, then install it and evaluate.

I've been thinking that the A/C condenser sitting in front of the radiator is a problem and that MB did not design the early cooling system with enough overhead to handle the added load of A/C in hot climates - sounds like you've found a solution to this with a 3 row offset core radiator.

I really like the swirl pot flush catch that you discussed. I also appreciate your knowledge of radiator cleaning with zinc chloride. I have a good feeling about the de-oiling and citric acid cleaning of my engine block - I ran a criminal amount of water through it to get it flushed out afterwards. Based on your post, I think my radiator needs a closer look. That 3 row offset rig sounds good.
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post #10 of 38 (permalink) Old 07-02-2014, 05:43 AM
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The new MB antifreeze is blue in color and requires the system to be flushed when making the change over. I got a can of Liqui Moly which is the recommended flush from Autohauzeaz (sp). The new antifreeze has a -0004 for the last four digits of the part number. The last stuff I bought was -0002. I guess the was a short lived -0003 for a while.
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