The OM603 was running great with no problems in 3 or 4 long drives I've taken recently. Needle always below 100c no matter what.

I did notice the MB blue coolant in the reservoir darken a bit, and some brown at the bottom of the reservoir tank.

That was bugging me, so I decided to change coolant.

Drained and filled with water a few times to remove all the old coolant, pulled the reservoir and cleaned it too.

Filled with tap and ran it a bit, got some rust again. Squeezing the rad hoses, I could feel the crunch of rust buildup inside.

Since the cooling system was performing very well despite all this, I decided to just try a flush and rinse, fill with coolant, and call it a day.

I couldnt find my leftover citric acid powder so after much research I wanted to try Fleetguard Restore Plus. It has citric acid, and described as chelating also, which interested me greatly since this is how Evaporust works and I've tried that and found it to work very well.

So I got a gallon (smallest size) at the local Cummins place, and in the parking lot drained some water from the rad, added a liter (mixing ratio is 1 liter/10 liters water), and drove home.

You need to keep it at operating temp for 2 hours and I got home before that so I left it running over dinner then drained it all after.

I wasnt expecting much, as I'd been draining amd filling it almost every day for a week or so and was getting decently clear water with a very slight tinge for a few days by then.

But what came out was surprising. Yellowish fluid with an acidic smell. Like muddy water. And some solid rust particles along with it.

But what really surprised me was I tried squeezing the rad hoses and they were all pliable now, with no crunch at all!

It looks like it really did a good job of melting away rust buildup. I'm tempted to do another flush but I dont want to overdo it and spring a leak somewhere lol!

I've been draining and filling a few times now and the water is clearing up with only a slight tinge. I will do this till the water runs as clear as I can get it, then flush with distilled water a few times then fill with some MB 325 coolant and distilled water.

Overall a very positive experience so far with this product!

The block drain on these is really easy to access. It has a nipple so it’s clean to use as well. I’d drain the block too. Burp air well…

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

^True! I'm thankful for the easy access, every drain and fill has been from the rad and block drain. And doing it all from the top side lol!

Just did another drain and there is still a slight yellow tinge to the water and slight chemical smell. Wish I had a garden hose to speed up the rinse process but Im doing this in a condo car park so its drain and fill and drain and fill.

I've used 1 lb citric acid w/ water as a corrosion remover in several cars. Not sure how much it helps. The chelating action sounds interesting. I also use Evaporust on small parts like nuts and bolts. My 1985 300D kept overheating when idling at a long stop light, creeping above 100 C. I tried many flushes, even removing the radiator to fill with citric solution and sit in the sun for a week. Ditto for a used radiator. Finally tried a new aluminum radiator when I saw them for $130 (vs $350 prior for a Behr) and fixed it. Tore the tanks off the old one and found just a coat of yellowish "mud" partly blocking some tubes. I could flake it off easy so don't know why when I ran a long metal grill brush over the top that hadn't worked. Maybe some other problem and the alum radiator just gives better cooling. Yes, I tried T-stats (several) and water pumps (several). I even removed the water pump housing to see if some debris like a rag was stuck in the engine. Problem was starting to drive me nuts over several years, but stays at 82 C all the time now.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Good to hear you got your temps under control, Bill.

As an update, I was finally able to backflush the system, I removed the thermostat and flushed it till clear, then refilled with distilled water and MB 325.0 60:40.

Past few days were very hot and I've been using the car a lot to test it.

Temps peak at 100c at the hottest part of the day in the worst of traffic, but most of the time it's at 90 or so. And the AC blows cold even at peak temps in standstill traffic, so I am happy.