rusty water issue?
 

I just had an overheating issue with the 85 300SD which I have sold to my daughter. I changed the stat (a chinese made one which must have come in it) and am crossing my fingers there is no other issue with the engine. My question is with the nasty rusty looking coolant which remains in the system after draining all I could without major effort. Is the rusty water look just a cosmetic issue or do I need to flush it really well?

Get some litmus paper and check the ph. Thats a great way to understand the worst harm the fluid could pose.

I ran a coolant filter a while back when my 617 had some terrible rust issues. After 3k miles, I cut open the filter to find about a hefty tablespoon of sand and finer material.

The worst that could do is erode the water pump... which has pretty beefy vanes and such a small quantity would have to pass by for quite some time to amount to any damage.

Look in the top of the radiator for larger debris. If you suspect larger pieces, they may be an issue in the water jackets in the block.

I have filled it and am running it now after flushing what I could and it is looking much better.

Thanks for the response! (The crank, bearings and such you sold me are in this motor and it is the sweetest runing mb engine I have had done yet and we spent the least fixing it!)

If you have one of those fancy IR thermometers it might be worth while checking for cold spots on the radiator after you've driven the car and it is all warmed up. Rust sometimes = clogged...

Thanks guys, it seems to be running fine so far. the short hose between the wp and tstat housing is seeping a little so when I get a chance I'll have to tighten that.

This is concerning. I don't remember ever seeing any cooling system rust in these cars. Sounds like something from a late sixties Mopar or something.

If it were mine I would want to THOROUGHLY flush the system including opening the block drain and even back flushing through there with a garden hose. Flush, flush, flush.... THEN go to an over the road truck shop and buy an additive called Nalcool. Put in fresh anti freeze, distilled water and Nalcool in proportions as directed.

Best of luck with it.

Yeah,well, ya gotta remember where Tom is. The local water has a high iron content. If you get your water from a well instead of the municipal supply it's pretty common for the reddish color to appear in the cooling system. When I was a lad in the scouts we didn't use canteens to carry water. Just carried a magnet and dipped it into the water. We'd scrape some water off the magnet whenever we got thirsty.;)

It would have been filled probably with well water after the motor install at my indies and he probably is on well where he is located.

Is Nalcool a rust inhibitor?

as many of you probably know, the benz diesel came with the inside of the block painted. since the motor has been gone through that was probably not replaced, hence a possibility for rust from the block which was not there from the factory.

Not so much as a rust inhibitor as it is a treatment for the coolant life but it will help. Not much you can do about the iron content than to try to use distilled or purified water as much as possible.

Distilled water $0.99/gal at Walmart, cheap insurance....

I remember the pitch that the Nalcool sales guy gave us at the truck shop ca. 1970's. He used a voltmeter and read about 1.5 Volts from the rubber mounted radiator to the engine. He poured in the Nalcool and then read 0 Volts between the two. In those days, there were zinc plates in the cooling system that acted as sacrificial metal for corrosion control. The Nalcool took the place of the sacrificial zinc plates by virtually eliminating the corrosion.

Yup, that was back when the automotive/trucking industries were still trying to figure out the electrolysis problems. Back in mumblety-mumble when I was working on Cats, Detroits, Cummins and Internationals it was a major problem with the mixed matches of steel, cast iron, brass, copper and aluminum used in the cooling/heating systems. Took them a couple of years to figure out why some blocks just dissolved internally.

Almost exactly a year ago, I went through my cooling system and replaced everything but the water pump. Radiator included. Despite several citric acid flushes and about 15 fresh water flushes, I still have mud colored coolant to this day. I finally just gave up getting it clean. I added G05 and distilled water and said F it. The rust stain is still in the parking lot where the nasty water came out all those times. FYI to be mindful of that when you flush the cooling system. Someone had been running straight water in it for an unknown amount of time.

My Indie shop friend told when he rebuilds a Mercedes engine, he never has a block tank cleaned because the water jacket is painted with a special coating. He always flushes them out with solvents.

Tom

A wise man. its probably lead paint!;)