"...my cooling system is perfect..."

There is no such thing. You'd look funny if tomorrow you roasted the engine after a hose blew.

Nothing in life is perfect. You've just been lucky.

The symptoms typically show up as excess cooling system pressure, and residual pressure after sitting for an extensive period (say, overnight). If your upper radiator hose is rock hard (can't pinch the two sides together) after sitting overnight, then you may already be a winner! The excess system pressure frequently pukes coolant out the reservoir overflow tube. This is how I first learned about my head cracks. I noticed coolant dripping out the rear of my right front fender. Turns out my overflow tank* was full of reservoir overflow. A new reservoir and cap fixed this symptom for quite a
while.

I'm now contemplating fixing this problem once and for all, now that my valve stem seals seem to have left the building.













*The overflow tank sits behind the fender liner.

I have all new conti hoses, by all I mean I'll I have like 3 original heater hoses behind the fire wall. Those will be swaped out, everything else is new.
New Behr radiator, OE cooling tank and cap, OE water pump, new Behr T stat. Both the viscus clutch fan and electirc work as they should, although since the viscus one is original I may swap it out for the updated plastic version anyway.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Good performance and durability, Trap Ox removed at 166K miles

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

Symptoms of the cracked head vary depending on the severity of the crack, and if the gasket has also failed or not. Anyway, a brief summary - if you have any of these things, it's not good:

1) Unexplained coolant loss with no external leaks

2) High pressure (say, 15-20psi) in the cooling system after the engine has cooled down overnight. This symptom may not appear if there is a leak in the cooling system, as the pressure may bleed off through the leak.

3) Oil in the coolant reservoir (but there's usually NOT coolant in the oil.)

4) Rapid, erratic engine temps under load - meaning the temp can go from, say, 85°C up to 105°C very quickly, and sometimes without a heavy load.

5) On my one car with the cracked head, I could release the cooling system pressure and drive it for an hour at *very* light throttle and have almost no pressure in the cooling system. But at any time if I gave it ONE full throttle burst through the gears to redline, to 70mph or so, it would instantly have high pressure in the system - with a new/good head, this shouldn't be possible.


Side note - OM603 engine temps may be 85-95°C normally. Just because some other diesels seem permanently stuck at 85°C does NOT mean that the 603 has to be there as well. As long as it rarely exceeds 100°C, and almost never approaches 105°C except under full load and high ambient temps, don't worry about it. If temps ARE too high without the conditions to warrant the high temps, it's time to look for the cause. Often this is from debris in the radiator or condenser fins (or in the space between the two), OR a faulty radiator (this is far more common than it should be, for reasons I don't understand), OR it can be from a fan clutch that is not engaging (which can be caused by the plugged fins OR a cold spot on the radiator - many clutches have been changed unnecessarily, so troubleshoot carefully.)

Oh yeah - the trap oxidizer has been suspected of being the primary cause of the cracked heads. However the damage can be cumulative. My trap was removed at 190k, but the head cracked at 230k with sudden, unexplained symptoms (high cold pressure). Removing the trap does NOT prevent future cracking. The original #14 head was still a flawed/weak casting, as noted in the OM603 factory service manual.

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Dave
Boise, ID
Check out my website photos, documents, and movies!

The No 14 on my L seems to be in order. The No 17 laying on my floor is crack free too.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

I don't have the coolant pressure problem nor any oil in the coolant. I guess my head is still OK. I do have some temp issues while going up hill. I took a good look at the radiator from the outside and noticed that the fins are full of greasy crud. I may clean it out but I have plans to sell the car as I don't want put any more $$ or work in to it.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

This definately happened to me one time on a trip to Baltimore a year and a half ago ... does it necessarily mean I have a cracked head or one in the waiting? I've on several occasions checked the up rad hose after sitting overnight and it has thus far always been easily squeezable. That time when the car drooled coolant out from behind the wheel, I took it to the mechanic who said I had the wrong resevoir cap (who knows how that happened), but everything else looked fine (he explained that the overflow tank had leaked the coolant). Between me not being very car-saavy (even less then than I am now) and my mech having a thick accent, I to this day don't understand why the overflow tank leaked. Are there reasons for it to do this other than a cracked head? It hasn't done it since.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

If there's little to no pressure when cold, and you are not losing coolant now, the head is probably not cracked. It could still happen in the future but don't lose sleep over it. Keep an eye on engine temps and if they get beyond 105°C, figure out what's wrong and fix it.

Your initial problem sounds like the cap was bad, or incorrect. This allowed coolant to flow into the overflow catch tank, hidden in the fender. That is not a sealed overflow tank - if enough liquid goes in, it will overflow out to the pavement.

That explains a lot ... I didn't realize that the overflow tank wasn't closed, so I assumed it would take a lot more to make it spill onto the pavement. I have to guess that bad cap was put on in the mid-90s when my mother hit a deer with the car and the radiator was replaced ... that's the only major repair that I have no documentation of, so maybe they screwed around with the resevoir tank at the time too.


I went through quite a long process surrounding running temps this summer ... replaced tstat, fan clutch, sender, because I thought the car was running a bit hot (95-100 on hot days, usually) ... after all that my indy did some temp gun exploration and discovered the temps were fine and the gauge was reading high. Given that fact, the temps have been great.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

For those that have experienced engine over heating or head cracking issues,
I am curious to know

1) What type (syn or dino)of engine oil do u use?
2) What type coolant (MB or after market) do u use in ur car?

Thanks

1) Mobil-1 or Delvac-1 synthetic, 5W-40, since immediately after purchase in 1997

2) Only Mercedes antifreeze from the dealer, or Zerex G-05 (which is the same thing). Don't use anything else... read this PDF for detals (1.7MB).

Dave, an interesting side note - Ford has recently adopted the G-05 coolant in the form of "Ford Motorcraft Premium Gold" coolant. I haven't had the chance to stop by my local Ford dealer and check the price per gallon though.

I had to have mine replaced last week. It was 17 thousandths out. He didn't even bother with the pressure test because it was too warped to machine.

with serious questions RE: the # 14 head on his engine.