You are not pre-glowing long enough. The glow plug lamp in the instrument cluster generally goes out after 5-10 seconds but in that weather you need to wait at least 15 seconds or more before turning the key.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

If glow plugs weren't needed on a NEW engine why would the engine have them?

The compression theory doesn't add up.

There's no blowby and it fires up immediately at the coldest temperatures.

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1993 W124 300D
-297K on the clock as I type this.

It stays on longer when it's colder.

When the engine is warm it only comes on for a few seconds.

It starts fine.

__________________
1993 W124 300D
-297K on the clock as I type this.

(Convincing oneself that a Compression Test is Un-necessary,
Based on "Blowby"[Or the Perceived Lack of it] )

Since Sixto has "Weighed In" ,I'll just shut up and Monitor the Eventual Results.

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'84 300SD sold
124.128

I'm out of my league here too but here's my reasoning - Going back to basics, a Diesel engine needs heat and pressure to effect proper combustion. If we assume the glow system is working because the engine starts easily and runs well for the nominal duration of the afterglow cycle, heat, at least as provided by the glow system, is not the issue. That leaves pressure. I presume that with any reciprocating ICE compression improves as the engine warms. On a good 602 this happens in a few seconds. It might be taking longer in your engine. If so, I can only think it's a cold compression issue.

What I expect a compression test to reveal is that one or two cylinders is misfiring when cold. Come to think of it, a balance test might be a simpler way to the same conclusion. Loosen each fuel line while the engine is idling poorly. My guess is you'll isolate the problem to one or two cylinders. Loosening the fuel line to a good cylinder may stall the engine. Loosening the fuel line to a bad cylinder will have little to no effect. With that information, you'll need a compression test and possibly a leakdown test across the board; if not for the actual numbers, then for the relative numbers between good and not so good cylinders. Or you'll find something simple like a bad or incorrectly installed heat shield.

It could be an injector or delivery valve or any other thing but if the engine runs well with the glow system engaged and runs well at operating temperature, compression is, to me, the most likely factor. Maybe there are prechamber faults that cause these symptoms.

Everyone, feel free to poke holes in my reasoning.

Sixto
87 300D

i-osprey you asked for advice and it was freely given with explanations as to why. Then you argue with those who gave the advice. I think CI has given the best response and ditto what he said.

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92 300D 2.5L OM602 OBK #59

Nobody but Sixto had any reasoning to explain their advice.

The exact same thing was happening before I replaced the injectors but now there's more smoke. I suspect I had a few bad injector nozzles that were underfueling.

If I do find that I have a compression issue what can I do about it?

Nothing, I presume.

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1993 W124 300D
-297K on the clock as I type this.

Could be something relatively simple like the typical head gasket breach into #1 cylinder. Maybe #1 has needs time to stabilize after a cold start because cold engine oil doesn't burn properly in a cold cylinder.

Could the rings be sticking when cold? Did this engine ever run on WVO or incorrect grade of engine oil? It might be worth a can of snake oil before tearing into the engine, but only as a last resort. A compression test should identify the culprit cylinder/s then a leakdown test can determine where how pressure is escaping; e.g., through the valves, head gasket, rings, etc.

Sixto
87 300D

Can anybody explain what changes the engines ability to create compression at warmer temperatures?

What exactly prevents it from being able to do so at cold temperatures, for example?

I'm clueless on this, obviously.

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1993 W124 300D
-297K on the clock as I type this.

It hasn't ever run on WVO to my knowledge.

I've had it for 35K miles now and it's only had diesel run through it.

I must say that looks like coolant is going somewhere.

I had a leak near the thermostat housing that I thought was the culprit. Come to find out there is a bracket there that holds a steel coolant line up against the thermostat housing. My bracket was loose allowing coolant to leak from around the o-ring.

I tightened it up and haven't seen any coolant leaks since but I have only checked the same spot.

Man, I hope I don't have a bad head gasket.

Also, this summer when I has having issues with my electric fans AND my fan clutch I got really hot a couple of times. I never saw it in the red but it got close.

Once, idling in a parking lot while near the red, I heard a "squish" sound and the engine died.

It fired right back up but I have never been able to resolve what caused that.

I'm not using any oil, either.

From what I understand a certain amount of oil is expected to burn off in these engines.

How much?

I typically have to add a little after three or four thousand miles but even then it only gets down to half way between the plastic pieces on the dip stick. That's well within requirements, IIRC.

__________________
1993 W124 300D
-297K on the clock as I type this.

If engine oil was causing this why would it start fine with only GP heat?

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1993 W124 300D
-297K on the clock as I type this.

Hmmm... At startup the prechambers, cylinders, cooling jackets are all at ambient temperatures. Only the compressed air and glow plugs are hot. When the glow plugs go off the surrounding metal structures are still cooler. The glow plugs may be masking a small leak, and once the structures get up to temp it masks the issue.
I'm still sticking with Black smoke = unburned/incomplete combustion fuel/oil, white smoke = coolant.

If its running good when its at operating temp then just keep an eye on things, and wait till it gets worst, otherwise do the compression test and report your findings.

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92 300D 2.5L OM602 OBK #59

I agree with the first paragraph. As for the latter part, my head gasket issue emitted quite a bit of white smoke, which was indeed the oil seeping into the first cylinder though the breach in the gasket. That said, after I replaced my head gasket, I still got a good amount of white-ish smoke until I figured out on GP wasn't heating properly. After I rectified that issue, the smoke went away... indicating to me that my issue was indeed one of unburnt fuel. Don't forget that weather can affect exhaust's appearance, too.

OP, does the smoke "linger" or quickly dissipate?

I still think it's very good advice to check compression. I am going to pick up one of the cheap diesel compression gauges at Harbor Freight even though my car appears to be running much better now. It's a very reasonably-priced tool that will allow you to very quickly rule out compression and at the same time, reassure you that you have a good, healthy motor.

Let me add this: if it turns out you DO have a head gasket issue, consider replacing it yourself. I just finished mine (FINALLY), and although it was certainly frustrating at times, it was an incredibly rewarding experience, and I couldn't be happier with the results (so far). You have an incredible resource in these forums, and legions of generous members who will help you get the job done.

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1992 300D 2.5T
1980 Euro 300D (sadly, sold)
1998 Jetta TDI, 132K "Rudy"
1974 Triumph TR6
1999 Saab 9-5 wagon (wife's)

Another thought -- when my headgasket went, I noticed a faint but regular clacking/nailing sound at first... and it built over the course of a couple of blocks 'til it became quite pronounced and was belching white smoke. Each time thereafter when I started it, it sounded fine with no smoke for a few seconds, but the smoke and rpm-specific clacking/nailing noise. The smoke hung it the air and dissipated with the breeze (while my unburnt fuel smoke would sort of "evaporate" even in still conditions).

My first sign that I indeed had a gasket issue was when I pulled the injectors and found the tip of #1 covered in oil. Hopefully you'll find that this is a much "lesser" issue that is more easily corrected.

EDIT: I just realized I am confusing your smoke issue with that of another member. I see yours stops smoking once warm, which mine did NOT do (when the headgasket gave up). My experiences may not apply in this case at all, but I'll leave them here for discussion anyway. Sorry for the confusion.

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1992 300D 2.5T
1980 Euro 300D (sadly, sold)
1998 Jetta TDI, 132K "Rudy"
1974 Triumph TR6
1999 Saab 9-5 wagon (wife's)

I appreciate all the input.

I would say that I'm not sure my smoke dissipates. It sits in a corner between a ten foot fence and a two-story garage so the wind does funny things there. My dogs hate walking in that corner when it's smoking. I am pretty sure that my smoke is unburned diesel fuel.

Have you seen those smoke machines college football teams use?

That "smoke" is unburned diesel.

I do occasionally have some annoying nailing/clacking at around 1100 rpm for some reason. When the tach goes above or below that it smooths out.

When I removed the injectors there was no oil visible. I just double-checked the old ones again and they are oil-free. Just a layer of carbon in a circle around the nozzle.

I have that compression tester from Harbor Freight but I still haven't used it.

It's very cold here lately and probably will be for the foreseeable future.

I also am not all that enthused about fiddling with all the crap I just "fixed" to do the testing.

I hope there is a fitting that fits into the injector hole.

__________________
1993 W124 300D
-297K on the clock as I type this.