300TD W123 radiator descale question - PeachParts Mercedes-Benz Forum

300TD1982 · #1 04-10-2017, 07:03 PM

I've had my W123 300TDT for 2 years. Recently I changed the coolant but there is still rust/gunk visible whenever I have a coolant hose removed. The radiator is an all metal one, and it weeps a bit around the seal at the top. I have a new Nissens radiator on the way. I plan to descale the cooling system with citric acid, but I'd like some advice with the order of operations.

If I descale it with the old radiator in place, I'm concerned that the citric acid will turn the weeping into a major leak. This isn't a big deal if I do it all in the driveway, but I'd rather drive around with the citric acid in the engine (I hear that helps the descaling).

If I replace the radiator and then descale the engine, I'm concerned that I'll plug up the new radiator with the crap I dislodge from the engine.

What would you do, and why?
Thanks for taking the time to help on this.

Rogviler · #2 04-10-2017, 07:09 PM

I'd do the citric flush before swapping the radiator personally, only because radiators and heater cores are the delicate parts so not subjecting the new one to that would be all the better. And yes, not clogging the new one would be another reason.

-Rog

Mxfrank · #3 04-10-2017, 08:53 PM

If you're concerned, install a Gano filter (search the web).

Diseasel300 · #4 04-10-2017, 10:47 PM

If the engine is really gunked up, be prepared for a surprisingly large amount of debris to come out. My SDL had enough crap come loose to fully block the radiator. Radiator leaked anyway, but the citric acid made it leak much worse. Definitely do the deed with the old leaky radiator in place, then flush WELL before installing the new one. The acid flush certainly makes a difference in cooling performance if you have a lot of scale in the system.

300TD1982 · #5 04-11-2017, 01:22 AM

Thanks folks! I'll definitely do the acid flush with the old radiator in place, and flush well afterwards.
The car has actually had no problem keeping itself cool. I'm just doing it because it looks like it needs it, and I heard it's important to do periodically.

I ordered a bottle of Shout Advanced Gel for the degreasing, and two pounds of citric acid for the flush.

My plan was to drain the radiator and block, then remove the thermostat, remove the top and bottom hoses on the radiator as well as the heater hose, then flush thoroughly with water by running hose water through the heater hose and through the top hose on the radiator.

Then reattach the hoses (leaving the thermostat out), mix the Shout with 2 gallons of hot tap water and dump that in the overflow tank. Run the car for 30 minutes with heater on, then let cool down. Drain, refill with hose water, run engine a few minutes. Do the drain-refill-run two or three times or until the water is not soapy.

Then reattach the hoses (still leaving the thermostat out), then mix the citric acid with 2 gallons of hot distilled water and dump that in the overflow tank. Run the car 30 minutes with heater on, then let cool down. Drain, refill with hose water, run engine a few minutes. Do the drain-refill-run two or three times or until the water is not slippery feeling.

Then install the new radiator, reattach the hoses (and the thermostat), fill with Zerex G-05.

I'd welcome any input into this plan! I'm a beginner, so don't hesitate to point out something that would be obvious to an experienced wrench wrangler.

Shortsguy1 · #6 04-11-2017, 09:29 AM

Please be sure to read about the potential downsides to a citric acid flush. My understanding is that it could accidentally eat through your heater core. My reason for mentioning it is that you said you don't currently have a cooling problem. So it would be really sad to make a problem where no problem exists. I normally think of it as a plan of last resort for people (like me) who cannot keep their car cool under certain circumstances. In your case, since you plan to change the radiator, some of the normal risk is not relevant, but I wanted to mention it anyway.

Diseasel300 · #7 04-11-2017, 10:44 AM

If the acid flush eats through your heater core or any other part of the cooling system it was weak and ready to go anyway, you were on borrowed time. The acid is not that strong (in the grand scheme of things) and doesn't react strongly with aluminum or iron. It DOES react strongly with scale and calcium and this is why it is used. Usually if you have a leak from the heater core (or radiator) it is because it had corrosion sealing a leak and the acid stripped away the corrosion.

That does bring up a good point: Be prepared for unexpected issues any time you do a major service (acid flushing the cooling system is a major service).

ROLLGUY · #8 04-11-2017, 12:47 PM

It might be best to bypass the heater core for the flushing process, and just flush it with water (both ways). Also, with the thermostat installed, the engine needs to be filled through the upper rad hose. Flushing can also be done with the upper rad hose off, so the dirty fluid does not even get in the rad.