Overheated tonight after losing my block drain plug. I had just wrapped up a whole mess of work on this car including a prolonged siege of flushing the cooling system, and just like all the times before, I left the block drain in there finger tight so I could drain that and the rad quickly. Well this time it bit me!

Was on my road test loop, noticed the temp gauge climbing higher. Got about 2/3 the way home (5 mile loop, maybe?), and turned on the heater, no heat. Uh oh. Slow down...gauge keeps climbing, hits the red, pull off at a fuel station, no water in the rad, only steam. Shut ''er down. Saw plug went away.

Glad I had just ordered a spare and it was delivered today, called my neighbors who happily picked me up, took me home, I picked up that block drain (really an oil plug drain off Amazon, but same thread, pitch and purpose), tools, and 3 gallons water, off we went. Filled the car with water, started it, looked around the engine bay, this is what I saw. No oil-coolant intermix noticed yet. Hope it just popped the gasket is all. No smoke on the way home, nothing unusual with oil pressure, oil level, or temps. All normal except this leak.

That said, what's the wisdom here? What am I in for? For notes, I'm a formally trained automobile technician, but work in corporate. Have tools and a (personal) shop. Looking for similar experience, should I expect a warped head, cracked block...pull it and tear it apart, or just go for the head gasket and all that comes with it?

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1983 240D 4-speed manual

Those engines are very robust and durable, I bought a 240D with the engine in pieces in the trunk, put it together and then accidentally ran it out of oil due to a ruptured oil pan which caused the pistons to seize in the bores due to the heat. After it cooled, replaced the oil pan, filled with oil and drove it daily for years with zero problems.

My guess is the head gasket was damaged due to the heat. The location of the oil leak is common. I'd suggest first doing a compression test to know what you have and then pulling the head to replace the head gasket along with all new bolts. Resurfacing the head necessitates removing the pre chambers which requires special tools or some ingenuity. When the head is off leak test the valves and address as necessary and replace the valve seals.

Removing the head on that motor has a few oddities I'd suggest getting a Haynes manual or the like. There are some hidden small bolts and the injection pump can get out of time if you aren't careful. Invest time in understanding the job first, it will pay off.

How many miles are on the engine?

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thanks Sugar Bear. There's 225k on the car. It was well maintained on the oil side of things. I noticed no difference in sound or performance before/after, I doubt I have done serious damage, but I do have a diesel compression tester, so I can make that happen. Looks like I need to get some paper OM616 manuals. I have read those available online and have a paper Haynes, but there's nothing like the real thing. Thanks for the tip on the bolts and valve checks. I can fill the bores with Varsol and check for leaks while the head's off.

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1983 240D 4-speed manual

Measure the timing chain stretch before teardown, you may want to roll a new one in. I've seen a few 240's break the chain and it breaks the cam towers and can crack the oil pan.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thanks for that tip. I had planned to do that anyway. No sense going that deep in and not doing a chain. Seeing that the front crank seal had been done makes me question whether that chain was done too. But, like you said, measure it and find out!

Took the car out one last time, after adding 1L NAPA Kool to the distilled water in there (indoor heated storage). Topped off the fuel tank with a dose of PS Clear Diesel for storage. Car is getting parked a while because I need to get my coach ready for a rally coming up. Headed to Kerrville, TX for the total eclipse. This car was to be my toad behind the '84 Wanderlodge. Looks like I have to pivot to my '69 F-250 instead. But I'll be collecting ideas and parts between now and when I snatch the head. Car still runs and drives great.

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1983 240D 4-speed manual

I know this is too good to be true. Did a brakleen wash where the oil leaked, drove car today and it's all dry there. Had a look at the head gasket from the Victor-Reinz kit I have and it seems there's a print-o-seal type at the edge, wonder if it got hot, leaked, cooled off and now everything's OK?

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1983 240D 4-speed manual

It's possible, it may be worth re-torquing the head bolts one-at-a-time or just leave it alone and watch. The head bolts are stretch bolts so...???

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

I'm in the latter camp. I'm still incredulous, so I took it to Costco and back tonight after caving and putting traditional green + Napa Kool into it. Coolant's cheap. Forgetting and leaving it outside in MI in winter is costly and painful. Still no signs of oil. That's after a good 70 MPH jaunt out I-94.

Been vigilant to noise or smoke, no changes. Oil pressure same, just above 2 bars at 770 RPM hot, tip in and it pegs. I think I dodged a bullet here. If the head does need snatched point-in-time so be it.

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1983 240D 4-speed manual

That is good news.

Watch both the oil for coolant AND the coolant for oil mixing in and obviously the loss of coolant, those motors run oil under pressure up through the block, through the head gasket and then into the head. Once in the head it goes into a cam tower/support and out through a pressurized rail with an orifice for each cam lobe. IIRC the timing chain gets oiled from spit off the front main bearing.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

The head expanded, because of extra heat, head bolts stretched more than normal,
best bet would be to retorque cylinder, special procedure required, than adjust valves.

Id recommend that you host your photos somewhere else. I can’t even see the leaks with the photos loaded on my phone. The PP software doesn’t host large photos. Use IMGUR.

How much oil is leaking in terms of volume? You could have warped the head and busted the HG but to me that’s a stretch.

If you stretched a head bolt, I think you would see a minor weep of coolant first. Some of the 5.9 Cummins, including one of mine, do this, and you see it weep out the front. Not a huge issue at least for a few hundred k miles.

I suspect you cooked the VC gasket, and the cover is a bit warped. Now it’s seeping at a specific spot. But again, photos are hard to see.

I love how easy it is to do coolant service on these cars, but this is a good reminder.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)