I couldn't resist snagging up a nice wagon with a few issues.

The main issue being that it overheats. Previous owner stated it was a cracked #14 head due to instant pressurization of coolant system, and it holds pressure overnight typically. The wagon can go about 1.5 miles before temps pushing over 90*C

It doesn't seem to smoke on startup, has slight chatter from lifters or injector knock, and might have slightly less power than my other 87 300td, but overall ran fine around the block before getting too warm.

I've got a diesel compression tester in the mail, and currently the intake is off, ready to tap into the glow plugs to test. The car only has 250k on the clock, so I'm hoping the rest of the motor is in good shape...

Outside of the (likely) cracked head, the only other ugly part about the car is some spots of rust in typical locations. The main areas are wheel well, and jack points, with a few spots elsewhere.

To get to the good parts about the car:
Zero dents
Near perfect interior
paint is in great shape
third row seat
working r134a air conditioning
Lots of work done within 10k miles before head issues, such as new front shocks, rear SLS shocks, brakes, various gaskets and belts, fresh tires

My goal is to get the engine running properly, and then start tackling the rust issues. The car was in Ohio most of it's life, but now that it's in northern CA, hopefully the rust won't move as quickly.

Nice one! I like how affordable these old benzes are when they need work.

It looks like it has a great interior but some seriously bad rust.

Just ran a compression test with a cold engine, testing thru the glow plugs

Cyl 1,4,5,6 all read 350psi, but 2 and 3 were just over 250psi...

Is this a sign that the engine needs to go? Or perhaps a symptom of a cracked head?

I'm slightly disappointed to see these results

Update: Looks like my fan clutch has gone out, as the fan spins about 10 rotations when I shut it off after warm. I've got a new one on order

The previous owner had a spreadsheet of things done to the car, which he shared. The last thing (20mi ago) he did to the car before claiming the head was cracked, was a coolant flush and thermostat. Squeezing the bottom radiator hose, I hear some air sloshing around the water pump area. Is it possible there is an air gap in my coolant system, causing the high erratic temps?

I'd like to rule out as many variables before tapping out and pulling the head...

If the upper radiator hose doesn't hold pressure overnight, is it a sign that the head isn't cracked?

Maybe you just have air trapped in the cooling system. It is an encouraging if the upper hose is soft in the morning.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Last night, I got the engine up to temp before shutting it off.

This morning the top hose wasn't rock hard, but after cracking the expansion tank cap, there was a surge of air, and one big bubble, that wanted to equalize with atmosphere. It did seem like there could have been some trapped air...

What's the best way to bleed air from the cooling system? Should I try removing the thermostat entirely, and see if that was the problem?

Take the cap off and drive around I like going upper and down hills for 20 minutes. Make certain the heater is on full blast as well. Good luck.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Thanks! I'll take a lap or two around the block with the cap off. Previously, one trip (1.5miles) would get the temp gauge over 105c

Yesterday, I tried running the engine with the cap off, looking for small bubbles. There were none, but after revving the throttle, I'd get a large surge of coolant slowly erupting from the expansion tank...

From a cold start to 105 in 1.5 miles sure sounds like a compromised head gasket.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Hmm, that's not quite what I wanted to hear. I'll still do the drive cap-off test real quick...

What's the ultimate test for a bad head/gasket? Cylinder leak down test?

I'm also going to double check that the previous owner installed the thermostat in the correct direction, since that was the last thing done to the car...

Yeah hey.... yes do that test drive without cap. Some will say to fill the coolant through the top hose either way works fine. No pressure build up over night in the hoses would mean a good head gasket. The bubbles can be so small you can not really see them in the overflow tank.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

I just got back from a 3-4min drive around the block without a radiator cap. Temps got above 110 within that time, starting with a dead cold motor.

Could I have a bad water pump? Clogged radiator? Failed thermostat? I mentioned the clutch fan has failed. Could having that not operating properly push me to high temps so quickly?

Those are possibilities as is combustion gasses mixing with coolant. Eliminate one at a time and good luck.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Just ruled out a backwards thermostat. I'm going to try running the engine without a thermostat, just to confirm. Although it looks like the previous owner did already try drilling it out with a few small holes. The system looked quite oxidized...

Clutch fan is in the mail, should have that installed in a day or two.