Effective rust removal for cooling system?

I only have classic (pronounced OLD) vehicles and frequently find the cooling systems developing rust internally. Usually, an off-the-shelf product works fine during a spring flush. But, I recently bought a classic Mercedes with a minor coolant leak. After replacing the radiator, i can't get the rust out of the system (it was bad). I've flushed it several times with every product the local parts store has. It's not as thick as it was before the repair, but it's still horribly murky. What would be effective, but safe for the block, radiator and rubber parts? I use PPG DX579 at work for metal cleaning prior to paint, but can't find any info about it being safe or not for aluminum, rubber, or a porous engine block. Any ideas?

Nothing I know of... had a truck that I flushed dozens of times with no luck. I wouldn't want to get after it with any chemical because anything with enough power to eat the rust will have enough power to eat the head gaskets. At some point you might be cleaning away what is left of the head gasket, and this isn't an mls gasket that is robust. I would just flush it out periodically over a few months time and live with it. Or pull the motor and tear it down, that is the only SURE thing.

I'll tell you what I did..

But first, let me tell you how stupid I am, and why I had to do what I did..

Replaced a water pump about 3 years ago.. Forgot to get some new anti-freeze, so I just
filled her up with water and said I'll get "roundtuit".

Never got "roundtuit". And about a year later started having some overheating problems..

Popped the radiator cap, and realized OOPs, I never put antifreeze in... It was some muddy
looking water..

For a few weeks, I would just fill it with water, waited until she started to boil over, let
her cool and dump it.. Repeat repeat repeat repeat.. About 3-4 times a day for 2 weeks..
During those couple of weeks, I also ran 3 or 4 bottles of the radiator cleaner flushing
stuff through, put a few days of driving on each bottle of flushing stuff... I probably
flushed her about 40 times..

After a few weeks the water coming out was only slightly tainted in color.. So I said screw it,
and buttoned her up with some fresh antifreeze, and she's been happy since.. Also in those couple
of weeks I had to replace the water pump.. The veins RUSTED off in only a year.. And I did the
radiator, just in case...

Here you can see the nice red stains left from the water boiling out the radiator cap.


And here is the old water pump next to the new one.. Can you see why it was overheating???

They make tees for the lower hose they allow you to attach a garden hose and backflush the system.
Bill D

I have an antique car that is a 1934 model and has a cast iron block. When I pulled the engine out for rebuilding, I found significant rust firmly attached to the cast iron, along with a lot of sediment. I consulted a specialist for the marque, who advised that the only effective way to remove the attached rust was to physically chip it out. It took a lot of effort to get the stuff out. Bead blasting the accessible areas was done as a final treatment. I suspect anything less would have resulted in overheating problems. I was fortunate that the severe corrosion did not eat through the casting. I have not yet reassembled the engine.

I find boiling Hydrofloric acid fixes the problem-o nicely....

This stuff is amazing.
I have never used their block cleaner but I’d be willing to try it.
Otherwise I’d use the concentrate after flushing thoroughly...pull out the thermostat...it might take a few doses.
https://www.rust911.com/rust911-home-page/

digger doug said:

I find boiling Hydrofloric acid fixes the problem-o nicely....

Click to expand...

Eeeeeep....
I had to work with anhydrous HF once.

They sell a 2 part can with acid one side and soda in other that works well.

We modify instructions as follows...

Open drain and allow water to drain while a hose is filling at same rate.

Engine at idle with a.c. on and it stays this way until drains clear.

Shut drain and go for short but aggressive drive then repeat.

Now put in acid and go for long drive then repeat above flush.

After second rinse add soda and repeat at long drive step.

When finished in your case just fill with water and check after a week to determine if done.

Repeat until "good enough" then fill with coolant.

Sent from my SAMSUNG-SM-G930A using Tapatalk

Strong vinegar/ water solution....let it run till hot, drain and rinse....repeat as needed

Rust settles in the bottom of the water galleries.
To remove it the best way is to knock the welsh plugs out, remove water pump, thermostat and all hoses Attack with a pressure washer, fire hose, air nozzle for an arvo. When the surrounding 1/4 acre is red you should be close.

Miguels244 said:

This stuff is amazing.
I have never used their block cleaner but I’d be willing to try it.
Otherwise I’d use the concentrate after flushing thoroughly...pull out the thermostat...it might take a few doses.
https://www.rust911.com/rust911-home-page/

Click to expand...

I would not use anything with an SDS like that. Absolutely no information.

tdmidget said:

I would not use anything with an SDS like that. Absolutely no information.

Click to expand...

The SDS on non toxic things is pretty empty.
I talked to the family chemist (yes we have one) he said he wasn’t worried.
Just another data point.

If you pull the thermostat to flush, watch the temperature close. Your thermostat allows coolant more time to cool in the radiator between open /close cycle's. Some engines will overheat quick without a thermostat.

Milkstone Remover every Tractor supply has it.

mllud22 said:

If you pull the thermostat to flush, watch the temperature close. Your thermostat allows coolant more time to cool in the radiator between open /close cycle's. Some engines will overheat quick without a thermostat.

Click to expand...

As weird as that sounds it’s true.
Use a clamp to choke down the outlet hose if it’s flowing too fast.

Shado said:

I only have classic (pronounced OLD) vehicles and frequently find the cooling systems developing rust internally. Usually, an off-the-shelf product works fine during a spring flush. But, I recently bought a classic Mercedes with a minor coolant leak. After replacing the radiator, i can't get the rust out of the system (it was bad). I've flushed it several times with every product the local parts store has. It's not as thick as it was before the repair, but it's still horribly murky. What would be effective, but safe for the block, radiator and rubber parts? I use PPG DX579 at work for metal cleaning prior to paint, but can't find any info about it being safe or not for aluminum, rubber, or a porous engine block. Any ideas?

Click to expand...

Please define what model of Mercedes-Benz you are calling a "classic." Also, allow me to suggest that posting your question on a make-specific site, and being specific about the year and the engine are needed to give you some guidance.

I'll suggest The Mercedes-Benz Discussion Lists - Home Page I hosted this mail list for several years, and while I no longer own a Mercedes (nor host the list), I'm still active on it. There you will find several competent people who kept (and keep) MB vehicles in good running order. We are talking primarily about post-WWII cars, from the 170 and 220A, through the pontons, finnies, later coupes and roadsters, as well as sedans. Most of these were built with a variety of engines, all of which have their oddities. If your are into a prewar car like a 540K, that list can give you some help as well.

As a generality, some Mercedes engines are aluminum, and most require running with a functioning thermostat in place and properly oriented, as the valve closes off warmup recirculation when it opens.
There is much more to consider than would be the case with a 1941 Cadillac or a 1936 Packard Twelve (both cars that I once owned and drove). Also, many of these cars require special coolant mixes, NOT Prestone glycol.

While automotive machine shop operations and practices may be cousins to operations discussed on this forum, many of them are not the same thing. Bringing a Packard Ultramatic transmission back to life generally involves regrinding worn parts and fitting and sizing new bushings; but these are one-off reworkings, not series manufacture of new parts.

Hank (Old Packard Guy)