I believe the thermostate works in the opposite direction most cars do......adn the manual calls for a jig that is a thermostat thats permananetly open....which on a benz will force water where it needs to go.....that would shorten the flushing process as a cold engine won't have coolant circulating everywhere it needs to be without it. No I don't have one but I have the time to do it the long way....

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Do the electric fan(s) come on?

The Electric fan on my W116 is A/C related.......since the A/C would be off I believe it would not come on....while I know my W116 fairly well by now I am not an expert on all the models.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

If the 6.9 is like the 4.5 in this regard, and I assume it is, there is a WT sensor that, at 212F, will kick on the aux fan. It should have come on in that traffic and when it got that hot.

I flushed my system with OTC rad flush, and a few clear water flushes after that, and it seems to have done wonders. What I recommend is, if you can't get the block plugs out (one per side of the V), then you will want to use a shop-vac. Put the bottom plug back in the rad, then suck at the rad neck (with the overflow port plugged). Then open the rad plug, drain that crap out, and do it again.

I wouldn't suggest the baking soda... for two reasons:
1) A pH too high is just as bad as a pH too low. You will get corrosion.
2) Baking soda, reacting with any acid left, would produce CO2 bubbles. These bubbles will rapidly reduce the cooling efficiency. Just make sure to flush it out really well after the citric acid, and if you can't get the block plugs open, don't even consider the citric acid, it will create far too much gunk in the block that you'll never get out!

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

My car, presuming it 's functioning properly starts the the electric overheat fan when it's warm out and the engine temp climbs regardless of the the A/C operation. Anyone else observe this?

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1974 240D 3.0L 4(M) - 250K -OM617.910 + 300D FW + Rajay turbo power!
1977 6.9 3(A) - 84k

Any idea where the block plugs and radiator drain plugs are on the 6.9's? Are they hard to get to without a lift?

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1974 240D 3.0L 4(M) - 250K -OM617.910 + 300D FW + Rajay turbo power!
1977 6.9 3(A) - 84k

The block plugs will probably be nearly impossible to get to without ramps or jacking the front end - they sure are on the 4.5! The rad plug on the 4.5 is on the right bottom ("right" as defined by looking from the back of the car, or as you would see it when driving). Dunno about the m100's block or rad plugs. Fire off an email to Gerry, Dan, or one of the other m100 owners if you can't find it.

Yes, my car will turn the aux fan on regardless of A/C status if it's above 212. I can also turn it on manually (I ran a switch to the driver's compartment).

The block plugs should be easy enough to find if you can get under the car to look around. There will be 1 for each side of the "V" and probably close to (if not at) the back of the block.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

There will be repeated flushes after the neautralizing flush.....but you are worse off acidic than you are alkalin...I did my W116 to fix the cooling issue but also installed a block heater at the same time...I am only familiar with the Diesel engine in these...if you can get the block plugs out....which should not be that hard..its the way to go....it migh save you from having to have the radiator rodded out or recored which is about the only other option.

Do nothing and its not going to improve or fix itself....

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

RE: the aux fan
in a 6.9 and others I am sure, it is controlled by the 212 Water temp switch on top of the thermostat housing. This will turn it on whether AC is on or not. Test your fan with key on and ground this terminal to engine . Also activated by pressure switch on the AC dryer next to the sight glass. Obviously AC must be on. The pressure switch is a double pigtail. Bridge these two and the fan runs.
Either of these locations is a good spot to run a switch in the cabin off of if you want control of the aux fan.

I am still looking for the block drains on the 6.9.

radiator drain plug is on the driver's side bottom. Kinda hard to get to with the chin spoiler. Don't need a lift for removing it, though.

This is a fallacy. Products like this DO NOT LOWER temperatures, your engine generates the same amount of heat regardless of the type of coolant you use. If you have a cooling system problem, GET IT FIXED, this is just a bandaid that will mask the symptoms but not fix the fundamental problems.

The best coolant for heat TRANSFER is water with a wetting agent. Heat transfer is what you try to maximize, this is what the radiator is for. If your radiator is not working properly, it won't remove the heat from the coolant properly and the engine temp will rise.

The issue of system pressure is a non-issue, these cooling systems are DESIGNED to operate at certain pressures, so the fact you have a fluid in there that boils at 212 (straight water) is not a big deal. Anti-freeze raises it to 250 (I think) and the pressure of the system even more. You could dump mineral oil in there and your engine could melt down before it boils. So don't think that boiling point is the only critical property of a cooling fluid.

__________________
MB-less

Where in Houston are you? I moved from there to Dallas 2 years ago. Never had any trouble with the 6.9 in Houston heat.

Fred

__________________
MB-less

Hell yes, thoroughly flushing the coolant system twice each year ranks up there with replacing hydraulic fluid and greasing kingpins on 108's and 111's as the *most* deglected maintenance chores. Then everybody wonders why radiators need to be recored, brake calipers freeze and suspensions wear out.

Emmerich, have you tried Evans Waterless Coolant ($20 per gallon) - probably invented for HumVees at Iraq - or are you one of those who just dismisses modern chemical engineering products out of hand as snake oil??

(edit: Hmm, guess i better get rid of synthetic oil in my '79 Benz because the car was not designed for it....... easily the best performance and longevity improvement I've made on the engine.