Hi folks:
Just replaced broken thermostat with Auto Zone wahler one. in my 1985 300D Turbo. All looks fine for last 2-3 days.
My Q is Do I need to remove the trapped air in these cars? And If so How? I dont see a bleeder valve on T-stat housing.
I was told that these systems are self bleeding. i also noticed that neither broken OEM nor new T-stat had any holes on them. Nothing is wrong now but just need to know to be sure and safe.

Thanks

MVK

__________________
One penny saved is three penny earned.

1985 300D Turbo 179,000miles

They are not self-venting and in my opinion poorly designed for venting. Both radiator hoses enter the engine at the top, which results in air being trapped in the block. My 77 has a vent bolt on top of the thermostat housing. Opening this does not effectively purge the system of air. Some people say just drive it until the air comes out. Others fill the system with the car on a steep slope with the back downhill. I fill mine via the top radiator hose to minimize the amount of air that gets in.
If I ever change out my heater hoses I may put in some kind of vent at the top of one of those hoses.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Thanks Kerry:
I huess I will just keep driving and adding more coolant-water mixture as the level falls. So far so good.

MVK

__________________
One penny saved is three penny earned.

1985 300D Turbo 179,000miles

trying running yhe heater at highest setting for ten minutes that worked on my deisel as well as my gas model........
William Rogers......

Thanks William

__________________
One penny saved is three penny earned.

1985 300D Turbo 179,000miles

I own a low mileage 1985 300TD. The engine's operating temp had been 80C (increasing to ~90C in the summer with AC running -as indicated on the gauge). As preventative maintenance, I just replaced the original water pump, radiator hoses and thermostat. The new Behr and the original Mercedes thermostat are both 80C. The local mechanic used Shell antifreeze (Mountain Dew color). The car had the green antifreeze from a Mercedes dealer. The car now runs between 90-95C. The mechanic replaced the thermostat thinking the initial one was defective. The car still runs at 90-95C. He verified the system temps with a digital thermometer. The thermostat outlet read 80C. The reading at the temperature sensor on the engine block read ~93C. The radiator cooled the coolant to ~83F.

I've read that some Mercedes diesel run in this temp range, but I'm concerned that I'd exceed 100C in the summer with the AC running.

I'm baffled why the car is running warmer. Can anyone please tell me why the car is running warmer?

So...the coolant entered the radiator at 80C and exitted at 83F? And then heated back up to 93C by the time it got to the head?

Didn't you replace an old, tired thermostat with a fresh one?

yes, the new thermostat has the same rating as the one I removed (80C). The new one was also replaced twice to verify the thermostat wasn't bad, but each one installed resulted with the engine running temperature at the same higher temp.

After one week of local driving (~30 miles) temp seems to fluctuate between 95C to ~102C (outdoor temp ~60F). Is there any concerns if the car operates between 95-105C?

This is a subject of much discussion on the site. As new, and typically for a decade or more, they run with the temperature gauge seemingly nailed to a needle width over the 80C mark. Then the temperature in traffic climbs, and eventually the "normal" operating temperature rises.

There are many threads on the subject, and it might be worthwhile to do a search on the subject. The actions that have been attempted over the years range from cycling through thermostats as some have found new thermostats less than fully functional to replacing pumps, fan clutches, radiators, hoses, and flushing with citric acid. MB thermostats are dual acting and when "tested" in a boiling pan of water the two moving parts that regulate the flow of water during warm up, normal operating temperatures and higher than normal operating loads (hill climbing, idling in in traffic with the a/c on or not, high speed operation, etc.) are not always easy to verify.

The system is an integrated set of components that work together to regulate engine coolant temperature. When new they work extremely well in the W123 Diesels. As they age, the range of each component's degradation from nominal performance leads to a new balance of integrated system performance. When this results in the temperature gauge needle moving perceptibly higher the operator enters the picture.

Unless the engine performance is degrading, meaning the efficiency is dropping and more of the energy from burning the fuel is being deposited in the coolant instead of being converted to torque at speed driving the wheels, the problem is in the coolant system. A systematic documentation of the operating conditions vs. the higher operating temperature can help - high temps at idle, for example, can be due to increased flow resistance in the coolant path that includes the radiator, or the heat sink (the air) flowing through the radiator. Any increase in flow resistance at idle is compounded by the low rpm of the water pump and the fan (lower pressure and volume from the pump discharge as well as the lower fan output in terms of pressure and volume of air through the radiator). The issues that add flow resistance can be mineral deposits inside the coolant jacket or radiator, the collection of corrosion products in the radiator from the entire flow path, and the damage to the fins between coolant passages on the air flow side of the radiator that accumulate over time (rocks and other objects that dent or scratch the thin, folded and painted steel on older vehicle radiators intended to increase heat exchange surface area eventually lead to blockages as the fins deform, the paint cracks and then corrosion gets between the steel fin and the paint, eroding the ability of the fin to transfer heat, and closing the air flow passage until the flow paths are entirely blocked on the lower half or third of the radiator).

Overheating at other operating points will give hints to the source of the problem - from fan clutches to water pumps to thermostats and so on.

But refilling the engine with coolant and failing to purge the air from the system will lead to poor performance that can mimic a variety of other issues. As already noted, I typically park the car nose up on as steep a hill as I can find, run with the heat turned all the way on inside the car, and fill with the engine running at "normal" operating speed. Newer MBs have a separate vent line from the thermostat housing to the expansion tank, which is fine, but I fill them the same way.

Good luck, and happy reading. This is a common, well documented problem. Unfortunately there is no clear and concise answer to a somewhat complicated system that can experience a broad variety of permutations of degraded component performance that are detected by the temperature gauge needle rising.

Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

By the way, I noticed that the replacement water pump was installed with the weep hole facing up. Does the orientation of the pump matter?

Hello,
I just wanted to post up what i recently went through with my cooling system...

issues that i was dealing with: black coolant and a leacking bypass hose


I flushed the coolant changed the thermostat with a new OEM one and flushed the system with clean water, i also replaced the bypass hose...

then the HOT running started with running at 100c to 105c with an out side temp of 20f! the thermostat housing read a constant 80c to 100c i pulled the sensors on the thermo housing only to find that niether one controlled the gauge... so i kept looking and noticed two more thermo sensor on the block the rearward most one did nothing to the gauge the front on however after simply disconnecting and reconnecting the sensor my car now runs at 85-90c with a highway temp of 90-95c...

so check all your temp sensor connections... there are 4 sensors two on the thermo housing wich control heater and glow plugs... the other two are on the passanger side of the block easy to see and get to...

Thanks all for the great advice. I haven't found the cause for the increase in operating temperature. Since the indicated temperature (~95C) seems to be near the range recommended by the owner's manual (94C). My plans are to leave everything alone until summer time. Hopefully with the AC and traffic, it will remian below 105C.

My SD suffers from the same malady.

It reads just about 100C. under all conditions and under all ambient temperatures. Doesn't care if it is 20F. or 100F.

The radiator, thermostat, clutch fan, water pump, and water temperature gauge have all been replaced over the past three years. None of them made a bit of difference.

My next, and probably last, suspect is the thermostat for the oil cooler. I believe that it has failed judging from the lack of oil in the cooler. However, I have a difficult time reconciling that this failure would result in 100C. temperatures with 40F. ambients.

I purchased a new one, but it's a real PITA to replace and needs a special tool.

Has it occurred to anyone, that instead of using colored coolant, you should be using Zerez G-05, clear coolant? The switch on my car resulted in a 5 degree drop in temp.

@OP, I would completely flush out the cooling system with a flush kit (with the vinegar smelling stuff), with the heater on full blast, and the engine running. After the cooling system is rinsed out, replace the coolant with the Zerex G-05. Also, disconnect the heater hose that goes to the thermostat area, and fill it from the back end, filling it to the thermostat. Then take it for a test drive!!!

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1983 300D, the "Avocado"
1976 240D, 4-spd the "Pumpkin", SOLD to Pierre
1984 190D, 2.2L, 5-spd, my intro to MBZ diesels, crashed into in 2002