My 1985 300D has cold pressure in the cooling system, from owning an om603 car I know that usually means blown headgasket or cracked head which is not common on the 617. The car has never overheated, runs great, doesn't lose coolant, and has some blowby but not excessive. Is there anything else that would cause this, or do I need to just pull the head?

You could do a leak down test or a compression test before pulling it apart

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I just had the same experience.... I drove my 300SD for errands the day before thanksgiving. The next morning, I see a small puddle of antifreeze on the right front of the car. Upon opening the hood, my coolant tank was filled almost to the brim, ( more than normal) and it was 47 degrees out. when I opened the radiator cap...spllosh! I got soaked with cold antifreeze.
History: 191K on the entire engine and car. I flushed it with citric acid 3 times this summer to clean it out...that was in july/august. Im thinking I removed rust around the head gasket. ( no antifreeze in oil)

I noticed a tiny bit of black engine oil in the top of an otherwise very clean cooling system. So, I drained block and radiator, but no additional oil to see.
I then flushed it with 10 Gallons of RO and some tsp, and refilled with RO water.

Ran it up to temp, and letting it sit with pure RO water, no antifreeze today, trying to see if more oil shows up in a still very clean system.

I am in Phoenix, and may need to pull the head myself, and take it to a shop that does mercedes diesels.

Can anybody help me with info on getting my head rebuilt? Or, know of a shop in phoenix area that can do an awesome job???

Steve in AZ

617 heads crack relatively commonly. i have had to toss three heads i was rebuilding and porting due to cracks between the PC hole and the valve seats or between the valve seats. the cracks don't tend to open as much as on the aluminum heads thus they don't present much as far as symptoms beyond slight residual pressure in the cooling system and maybe slight coolant consumption or contamination. they can however grow with time to become a real issue but thats a hit or miss thing i suspect its dependent on how hard you run the engine and peak sustained egt you regularly see. something else to consider is the head gasket also can fail softly with the most common being between the no 3 combustion chamber and one of the outboard head bolt holes. this isnt really an issue though as all it does is lose a tiny bit of compression pressure. the way to tell is when you pull the head bolts they are covered in soot or a hard black plastic like substance from combustion products leaking. all in all there are many ways the head can technically fail however so long as you keep an eye on how the engine is running and if its using an appreciable amount of any fluids like coolant or oil i would just keep running it. if it gets worse like overheating or begins to use coolant then i may think about putting a rebuilt head on it.

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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
KD9AFT
A&P

Do they also crack with cold climate?

Well, if you don't have appropriate levels of anti freeze in it....?

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

It depends. Speaking of engines in general, thermal shock plays a large role in cracking.

Start a cold engine and run it to full power will impart huge thermal stress on the cylinder head. Rather than everything expanding at an even rate, the combustion chamber side of the hear expands but the coolant side does not.

When coolant gets to thermostat opening temperature the first time from a cold start, a slug of cold water from the radiator hits the engine creating a thermal shock. This effect is most pronounced with a thermostat location that regulates coolant flow out of the engine. Thermostats that regulate coolant into the engine are less prone to thermal shock.

Warm climates offer less thermal swing so the head should last longer if not overheated.

I always let it warm up (15mins) before driving it.