1985 300D with 200K miles will run for weeks with slight to no coolant loss, at about 80 degrees C, then for no apparent reason, lose a bunch of coolant, & begin running hot. No noticeable leak.

One nite last Fall, it went down to 12 degrees F, and later noticed a pool of coolant on the ground. Put a sample in the freezer, & concluded it just barely froze, put a richer mixture in the car, warmed it up, some leaked, & put the car away for the winter.

Just filled it up with water/coolant mix, it took over a gallon, and started it up and ran it about 1/2 hour. No coolant leaked, resevoir went down little or none, temp guage at a cool 80 C.

What gives?? Are the freeze plugs spring loaded and fix themselves?
Izzit the pump? Baffled !



Several 300D's in varying states of decay, and an '81 240D 4 spd with 90 K that is my favorite of the herd. All run on WVO, unconverted, summer only.

Cooling System Pressure Tester Kit


.

__________________
ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

I just had some problems with my cooling system. Saw some water leaking from the thermostat area but not from any of the visible hoses.

There is a very short section of hose on OM616 and OM617 engines that tends to get ignored during normal maintenance cycles. It can be a real pain to get to. It is between the thermostat housing and a lower heater hose connection on these engines.

My hands still have grease spots after having repaired this item 4 days ago.

__________________
Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)

Could be a failing water pump?

__________________
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

Never had a noticeable amount of coolant appear on the ground 'til the one cold nite where the coolant probably froze to a slush.

Could the pump also react to the cold?

Did the freeze plug pop partially out and reset itself?

How does one go about replacing freeze plugs? I ordered a set from Peach as i thought that might be the problem and they are cheap enough.

thanx

When it comes to intermittent coolant loss, the water pump shaft seal is at the top of the list of likely culprits.


If "it" did, you need to contact the Guinness Book folks.

I am new to MB, but with older American cars intermittent large amount of coolant loss is almost always the water pump seal. It can heal for a while then let go either when hot or cold.

Freeze plugs will not reset them selves, and they are not spring loaded.

I replaced some on a International Harvester V8 years ago, and on my Datsun Diesel. I used a punch/drift on one side to get it to turn. will pivot on it`s axis. then use some Vice Grips and pull it out. clean out the hole, apply some sealant. then using an appropriate size socket, gently tap it into the hole. careful not to knock it all the way into the water jacket.

Are you sure that your Freeze plugs are the culpert?

Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

After the brush with freezing, the loss of coolant was much greater than previous episodes, so i was sure @ the time i must have frozen it, as i stuck a small vial of the coolant in the freezer, which runs about the same as the outdoor temp that nite, and the stuff froze not quite solid, but to a thick slush.

That was the first time i noticed coolant on the ground under the car.

But if freeze plugs can't fix themselves, i guess it must be the pump.

Thanx for the help with this, will check back again for any more ideas.

I had a spotty connection on the upper radiator hose. It was leaking at the bottom of the clamp, hard to spot. But it was leaving a puddle every time I parked. I finally noticed a drip trail inside the radiator shroud.

What was happening is that it was only leaking under heat and pressure, when cold it would not leak.

Long story short check the simple stuff first.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Intermittent thermostat? If system makes a pressure test that is.

x2

__________________
Never be ashamed to ask for help.

1985 300D
1987 300SDL
1970 Jaguar E-Type OTS
2002 Dodge Intrepid (Traded In)
2011 Ford Crown Victoria

I've been on this forum for over 10 yrs. Can't recall reading a post regarding a failed freeze plug.

__________________
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

x2. When it's cold, everything shrinks, including your radiator nipples and hoses. Make sure they are clamped down tight (but careful not to over do it or they'll shatter. It could be the water pump failing as well, but I'd definitely go over the clamps and hoses first. Also, if you are using proper coolant you should see white residue from wherever it is leaking from.

__________________
TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

I've heard of freeze plugs corroding and leaking, but i guess if one actually failed due to freezing, it would be leaking copiously when refilled and run a half hour.

Will give it another look see now that the sun is finally out!



I'