Citric acid flush: one detail unsure of...

[Shortsguy1]

Hi, the process of doing a citric acid flush is the same for my OM615 as it is for all the OM61X engines. The FSM states that you should remove the thermostat before de-oiling the cooling system and doing a citric acid flush (20-015 of FSM).

But as I understand it, coolant will likely bypass the radiator without any thermostat in there. So should I install a forced open thermostat to ensure my flushes go to the radiator? If so, does anyone know the easiest way to force open a thermostat? I have an old one I am willing to damage, but not sure what is best.

An alternative option that has been suggested in previous threads is to get a cork to plug the hole that the thermostat normally covers when opened. Would this be better than forcing open a thermostat? I worry it could come loose and cause problems during the flush and rinse cycles.

Or, I could just follow the FSM and accept that much of my flush isn't going into the radiator. Any thoughts?

As an aside, I figured out why I couldn't find my coolant block drain. I had looked at the FSM and photos on the forum of the block drain, and simply couldn't find anything that looked like that on my car. It turns out my old OM615 has a little stopcock (i.e., valve) on the block to empty the coolant. Who knew! (probably some of you). It opens with a twist of the wrist, so that will make flushing relatively easy.

As a second aside, I am aware of the risks associated with a citric acid flush. I plan to avoid the heater core to reduce some of those risks. But my little car had green coolant in it for a long time and has internal rust which I want to remove. It runs way too hot at load, and this is one of the things I need to do to address the temperature problem. Thanks.

[Zulfiqar]

I have used a rubber cork in the bypass hole on my OM606 engine, works nice, It makes sure the cooling circuit is positively engine - radiator - engine, not engine-engine + some radiator.

yes you need to deoil it first - shout stain remover is good for this, I have flushed mine and some other cars too with a 5% solution without ill effects, Dont go over 30 minutes with the acid in the system. Flush completely, ideally you would need to cobble up a garden hose fitting for your upper radiator hose (use a general purpose autozone hose) and use the hot water supply tap from the washing machine if you can.

If you cannot then wait for the engine to cool down before you push cold water in it.

My drained acid had turned to an opaque caramel color the first time, after another 6 months I did it and it turned only slightly yellow. Since then the coolant is pretty clean but my expansion tank has collected a nice coating rust colored something.

[macdoe]

Curious about the citric acid flush after reading your posts. I have always wondered why all the tendancies to do this if it is a potential hazard for certain parts in the cooling system. I did not realize it is a procedure in the factory service manual.

I have a small issue with the car getting slightly hotter under load, as you do. Seems that it will get a wee bit hotter at highway speeds when cruising at or above 2500 rpm. I have only noticed a needle or 2 width higher than normal, which is no big deal and it does'nt pass the 90 degree mark. It does'nt bother me cause I have passed it off as a normal operation. We did the head in this car (85 wagon) before winter and I know I got lots of oil in the water jacket when cleaning /tapping the thread holes for the new head bolts.

It will cool down again after reducing RPM's to about 2200. I also wonder if the turbo has something to do with what I am seeing, or maybe it just needs to be flushed again.

What is the whole story behind the citric acid flush? I think it is a given that it would clear scale and accumulation out but is there a reason for expecting oil in your cooling system under normal conditions, meaning even if one did not take the head off and inadvertantly spray oil in the water jacket? Does oil just leak through the pores of the metal over time, causing this slight increase in temps due to heat transfer being obstructed due to oil in the water passages? Curious as to your use of the term de-oiling the cooling system....does it actually use those terms in the service manual?

[Shortsguy1]

De-oiling is also a term from the FSM. They recommend some german cleaner which I have never heard of (Henkel P3?). As suggested above, Shout is often used here as a substitute. You just don't want something that will foam/froth on you. It says you must de-oil before doing a citric acid flush, even if no evidence of oil is present. If your engine has been working correctly, I have no idea where this oil would have come from. So the de-oiling is different than the citric acid flush which could follow. The acid is intended to scrub/clean rust and scale from the interior passageways of the engine and radiator. I used a Prestone flush a year ago, and lots of rusty water was flushed out. But I still have the problem and am willing to be more aggressive looking for solutions.

I think some people have experienced failures (radiator, water pump, etc.) after performing a citric acid flush, but I am willing to risk it. Some say that those failures were likely to occur soon anyway, and the citric acid just accelerated the failure a little.

Anyone know how to force open a standard thermostat?

[sassparilla_kid]

Does anybody think adding an extra loop (small one) with a filter to remove rust and other crap would work? If so it seems like a simple enough solution to help keep the system somewhat clean

[compress ignite]

What if it becomes occluded ? (Stopped Up)
Y'all must NOT totally restrict the coolant flow.
Else Wise,Suffer ALL the effects of engine meltdown caused by OVERHEAT.

[compress ignite]

I'll be honest with you...

I'd rather replace questionable coolant system components,
than chance Ill effects from a "Citric Acid Flush".

Flush the Block and Head, O.K.

Everything else gets R+R ed.

[sassparilla_kid]

Originally Posted by compress ignite

What if it becomes occluded ? (Stopped Up)
Y'all must NOT totally restrict the coolant flow.
Else Wise,Suffer ALL the effects of engine meltdown caused by OVERHEAT.

I'm not talking about putting a filter anywhere that might cause problems if it gets plugged up, but maybe a small 1/4"-1/2" line maybe going parallel to the heater core, if that makes sense. It wouldn't be restricting any of the normal flow, although in theory all of the coolant would make its way through there

Kind of like post #89 here, although this is in the intercooler loop I believe. Same concept though

ForcedInduction's 1982 300D

[Shortsguy1]

Originally Posted by compress ignite

I'll be honest with you...

I'd rather replace questionable coolant system components,
than chance Ill effects from a "Citric Acid Flush".

Flush the Block and Head, O.K.

Everything else gets R+R ed.

If cost was no object, sure that is a better approach. But I am willing to spend $20 on parts (shout, citric acid, water) and an afternoon of my time, to try to fix things first.

My radiator is an all metal OE behr radiator from probably 20 years ago. Sure it is old and probably needs replacement. But an new OE radiator is $1000, which is money I don't have to spend on this car. A cheap behr modern equivalent is $350 via ebay, which some say are now made in China and the plastic necks break. And my car is before MB used oil coolers, so radiators from salvage yards typically are not compatible (without losing heat transfer area to an oil cooler which not being utilized).

So after my afternoon of playing in acid, if I do blow a hole in the radiator, I can get it fixed or replaced then.

I think part of it for me is wanting to try out each solution, one at a time. Rather than change a bunch of things at once, I am doing it one step at a time to really try to understand the culprit of why my car is running way to hot at high load (230-240F). Obviously this is time inefficient, but that is how I like to approach these sorts of puzzles.

Does anyone know how to force open an thermostat?

[Zulfiqar]

Before doing the flush you may want to remove the radiator and clean out its cooling fins and the condenser cooling fins with some condenser cleaner. If there is low heat transfer at that area your system maybe squeaky clean inside but may never remove heat as quick as required.

This situation also makes the fan clutch not work.

[pwagon]

Have you done a flush with just water and seen if that's enough?

You may not need the acid.

I went right for the acid when I did it and it opened up holes in the freeze plugs of the engine block. My radiator was clean but now I was leaking coolant.

There was nothing I could do but let it leak coolant until it rusted shut again.

Beware the acid flush!

[Shortsguy1]

Pwagon-
Do you remember what concentration of citric acid you used and how long it was in the engine? I am okay damaging the radiator or water pump, but I would get very frustrated if I went through what you experienced.

1 year ago I got the 220d from my mom. It had sat untouched for 8 years since my dad passed away ( it started right up by the way... didn't have to charge the battery!). It had green coolant which I flushed via hose. I used a Prestone flush at the time and tons of rust came out. I then rinsed via hose and filled with Zerex G-05 (or whatever it is called) at 50/50 mix ratio with some hose water and some distilled. I could not find the block drain at the time.

Since then, I have cleaned with exterior of the radiator with simple green, hose water, spray condenser cleaner, and a dental pick (to remove bugs/pebbles). I have straightened all the fins. I have removed one of my two horns because it is right in front of the radiator. I have removed an electric supplemental fan because it blocks air flow at high speeds. This also helped me clean the radiator very well. So the exterior of the radiator is as good as can be expected for an old radiator.

I have a new thermostat which opens at 79C. The car at 60-65 mph on flats or around town runs at 185 F (85C) on a 75 F day. But up hills at highway speeds or at high speed (75+ mph) on a 75 F day, the car will reach ~240F and probably go higher if I let it. I have verified that my temp gauge is reading within a few degrees of correct.

I did a Red Line water wetter experiment last weekend. I ran the car up a local hill prior to adding water wetter (my car reached 235F) and then I removed a little coolant and replaced it with water wetter. The car then reached 240F before I chickened out and slowed down. I don't blame water wetter for the change as it was probably due to some subtle change in weather or my driving habits. But the bottom line is for me, with a ~50/50 mix of coolant, water wetter did not help.

My next steps include:
citric acid flush of engine and radiator (not heater system)
the refill with 35/65 coolant/water

if that doesn't fix it, I will then replace the faulty fan clutch (probably not a likely solution since my problems are at high speed).

if that doesn't fix it, I will then replace the water pump.

if that doesn't fix it, I will have a shop see if they can improve the radiator

if that doesn't fix it, I will buy a new radiator

if that doesn't fix it, I will go to water+water wetter with no Zerex

if that doesn't fix it, I will avoid hills or high speeds

if that doesn't fix it, I will just sit in the parked car and make vroom vroom noises myself.

But without air conditioning, I may overheat.

[Graham]

Originally Posted by pwagon

Have you done a flush with just water and seen if that's enough?

You may not need the acid.

I went right for the acid when I did it and it opened up holes in the freeze plugs of the engine block. My radiator was clean but now I was leaking coolant.

There was nothing I could do but let it leak coolant until it rusted shut again.

Beware the acid flush!

I am about to install a new water pump on my R107. One pump manufacturer says that their warranty does not apply unless the system is flushed before installation. But they don't explain what they mean by "flush".

As already reported, MB describe de-oiling flush and acid flush in their manuals. First is probably a detergent, second citric acid.

Prestone, Valvoline and othesr sell flushing fluids. They seem to all be one-step flushes. So what do they do? Deoil and acid flush all in one? That is not explained.

My 72 has no problem with cooling. Original rad, can't recall ever flushing! No leaks except at pump. I am concerned about what an acid flush might do! Thinking of only doing a water flush, but tempted to use teh Prestone/Valvoline 1-step flush.

[funola]

Are you losing coolant? Have you pressure tested the system and cap?

[Shortsguy1]

I am not losing coolant. I filled it up a year ago and haven't had to top it off at all. I probably only drove 2000 miles in that year, but still there is no evidence of coolant loss.

I do worry a little about a blown head gasket or cracked head because I made the stupid mistake a year ago of flushing the engine while it was hot with hose water. I have no real evidence of this sort of problem, but I do feel pretty stupid for doing that. Once I realized what I did, I honestly thought I had ruined the car with my dumb decision.

I have a old radiator cap, and probably should fit it with some sort of pressure tap so I can measure the pressure of the system. I know it builds significant pressure because when I opened the cap with a hot engine (to add water wetter during my experiment), I got sprayed with coolant (boy, I feel smart as I write this). I also know that I have reasonable pressure because of the high temps my car has experienced without boiling over. My radiator cap is 1.2 bar, but I don't know for sure what pressure is being developed.

Thanks for all the thoughts and suggestions.