Overheating & How To Mix Citric Acid Flush - PeachParts Mercedes-Benz Forum

long-gone · #1 08-28-2009, 10:52 PM

I just finished the head/top end overhaul of my 1991 300E 2.6.
It started right up and and runs/sounds great. Only thing I did wrong was forget to hook the trans cooling lines back up and pumped about a quart of fluid all over, d'oh!
I still need to flush the cooling system though of all the oily goo left in the nooks and crannies. I put back on all the old hoses and radiator and I'll put the new ones in after I flush it out well and then give it the final fill.
With the thermostat removed, car running and heater on high, it would only take back a gallon and 3/4 of water. I let it run for about 5 min waiting for it take up more water out of the res but it never lowered any more. It wanted to bilge it back out even with the car running. I took it for a short spin and the temp rose to just below the red line. The aux fans kicked in and kept it there till I got it back home (maybe 2 minutes tops). The reservoir was still full. The radiator water tank on the water pump side was steaming hot while the tank on the trans line side was hardly warm. The top hose was very firm, almost hard, with water pressure. I know I'm supposed to bleed the air out of the system with the water jacket plugs on the head and/or the air bleed on the thermostat housing, but I'll have to do that when it's cooled down. Not knowing how to mix the citric acid yet I added a few blobs of shout laundry detergent just as a preliminary cleaner.
I've read as many threads as I can here about flushing the cooling system and different flushes used. I got a bottle of the citric acid powder from the MB dealer but there are no instructions with it. Some of the threads mention
10 or 15% solutions but don't instruct on how to achieve that. Is a 10% solution a tenth of the bottle to a gallon of water?? One thread said you need 2.2 pounds of acid powder to properly flush a system. Is that in 10% increments or all of it mixed with x?x gallons water in one flush?
Also, several posts recommended de-oiling the system prior to flushing. Isn't that what the flushing is supposed to do!? or is there a preliminary "de-oiling" step before flushing. I clicked links supposedly leading to tech articles somewhere her on the subject but they were dead links.
Has anybody here done this and can lend their experience? I'd really appreciate it, Thanks!

workerunit · #2 08-29-2009, 12:25 AM

Did you replace the thermostat and are you going to replace the radiator?

I would go with a slightly cooler thermostat and a new Behr radiator as well as a 1.2 bar expansion tank cap.

long-gone · #3 08-29-2009, 12:35 AM

Yes, I have a new Nissens radiator and a 189° thermostat. I still have to get a cap.
I just don't want to do the acid flush before I know how strong to mix it.

long-gone · #4 08-29-2009, 05:27 PM

Just bumping this to see if I can get some help from someone who's used the citric acid flush before. Thanks.

compress ignite · #5 08-29-2009, 07:17 PM

Your part # is: 000 989 10 25 (500 grams)

Mixed @ a strength of 100grams per liter of H2O.

Heater controls set to FULL HOT

Run,at operating temperature @ IDLE,(you'll have to let it warm up, AT IDLE) 5 minutes.

Flush,Flush,Flush ,fill with clean ,clear water and run up to Operating Temp...
then Flush ,Flush,Flush.(You don't want to leave ANY CAF in the system)

Use Block Drain Plug(s) as well as Radiator drain plug.

AT one point the FSM wants you to remove a bolt on the horizontal surface of the head to allow proper Refilling of fresh coolant mixture ???? "Burping"

[I'd Await ADVICE from EXPERTS on the advisability of that procedure AND
the Location of said "Bleed" Bolt...The FSM HAS any number of incorrect
pictures detailing instructions that would result in Engine Fatality if followed.]

I'd fill New coolant mixture with the chassis (Front) up on ramps...Mixture
poured into both the top radiator hose ends (Not simultaneously) to fill the
Radiator and then the Block.

Chas H · #6 08-29-2009, 07:25 PM

Citric acid won't do much to oil in the cooling system. Use Simple Green first to get the oil off the mineral deposits so the citric acid can get to them.
I think you need the thermostat- to close the bypass as the engine warms. I recommend you use a thermostat of the correct temperature. Using one that is rated cooler can cause the fuel injection to run rich.

compress ignite · #7 08-29-2009, 07:35 PM

Chas, Pardon my stepping on your advice....But,Simple Green does Ugly things
to Aluminum.

Dawn dish detergent ,in solution with water [or "Shout"] (may require Multiple applications)
will De-Oil the cooling system... Then Flush,Flush,Flush.

(Same procedure for De-Oiling as CAF ,Warm to Operating Temps @ Idle and run
for 5 minutes @ IDLE...with heater on Full Hot.)

I do concur about the correct Temp thermostat application (ONLY)for your Chassis/Engine...
Re-engineering the Mercedes cooling system with a positive outcome just ain't gonna happen.
[USE a "MERCEDES" Thermostat ONLY.This is one application where saving $20.00 is foolish]
AND test the Thermostat,in a slowly increasing temperature, pot of water.
[Do Not get Caught by the Empress of Cuisine,using one of her Cookware(s)]

Unfortunately,Horror Stories Abound of Owners driving for extended periods
using CAF as a Substitute for Coolant Mixture..."I'll Clean it out,Really Good".
The system (especially the WATER PUMP seals and Bearings) HATES exposure
to ACID LEVELS ...AND will notify you by decomposing as you drive.

long-gone · #8 08-29-2009, 09:10 PM

Great! Thanks for the recipe for the citric acid mixture. Not having any advise earlier I ran a little shout through it. As mentioned, the car overheated (got up to 120°, just below the redline but just momentarily. The recovery tank was belching and boiling over vigorously. I flushed it out after it cooled some. Today it ran a lot longer before it got too hot. I ran through a few gallons of acid, probably close to the mixture just suggested. Once again though, after a short while it heaved up out of the recovery tank. The oil goo just sticks to everything though. Some comes out but there's a blobby film over everything.
I think the over heating is because the radiator is all gunked up. I may have to put in the new one just to be able to flush out the rest of the system. There's just doesn't seem to be enough circulation now.

On the M103 there are a couple threaded plugs at the front of the head along side the valve cover on the intake side. I believe either one of these is used to de-gas and check the water level in the block. There's also a bleed on top of the thermostat housing.

Chas H · #9 08-29-2009, 10:28 PM

Quote:

Originally Posted by compress ignite

Chas, Pardon my stepping on your advice....But,Simple Green does Ugly things
to Aluminum.

Dawn dish detergent ,in solution with water [or "Shout"] (may require Multiple applications)
will De-Oil the cooling system... Then Flush,Flush,Flush.

(Same procedure for De-Oiling as CAF ,Warm to Operating Temps @ Idle and run
for 5 minutes @ IDLE...with heater on Full Hot.)

I do concur about the correct Temp thermostat application (ONLY)for your Chassis/Engine...
Re-engineering the Mercedes cooling system with a positive outcome just ain't gonna happen.
[USE a "MERCEDES" Thermostat ONLY.This is one application where saving $20.00 is foolish]
AND test the Thermostat,in a slowly increasing temperature, pot of water.
[Do Not get Caught by the Empress of Cuisine,using one of her Cookware(s)]

Unfortunately,Horror Stories Abound of Owners driving for extended periods
using CAF as a Substitute for Coolant Mixture..."I'll Clean it out,Really Good".
The system (especially the WATER PUMP seals and Bearings) HATES exposure
to ACID LEVELS ...AND will notify you by decomposing as you drive.

Citric acid will do a number on aluminum too, if it ain't flushed out. Dishwasing detergent tends to make lots of foam when used in the cooling system which makes it a real pain to flush out.
Misuse of most any product can lead to problems.

long-gone · #10 08-29-2009, 11:08 PM

I read several suggestions that the thermostat be removed for flushing. Ae you guys saying that the thermostat be left in?

My old thermostat was literally broken when I took it out, so I removed the guts and put the round brass plate back in (to support the o-ring so it sealed well) for flushing.

Chas H · #11 08-29-2009, 11:37 PM

Quote:

Originally Posted by long-gone

I read several suggestions that the thermostat be removed for flushing. Ae you guys saying that the thermostat be left in?

My old thermostat was literally broken when I took it out, so I removed the guts and put the round brass plate back in (to support the o-ring so it sealed well) for flushing.

I'm not familiar with the details of your thermostat, but many MBs use a bypass to circulate water in the block when the engine is cold. The thermostat has a disc that blocks the bypass as the thermostat opens. If you run the engine without the thermostat the coolant or what ever you have in there can circulate around in the block and not make it to the radiator.
The instructions are generic, so you got to pay attention.