[B]Q: Will all #14 heads fail? [/B] A: No, probably not. But they are known to be weak and must be treated with respect. [B]Q: If I buy a car with no "cold pressure" or other symptoms, and I never see the temp go over 100C, does that mean the head will never crack?[/B] A: No - sorry guys. The overheating incident can happen months or years prior to actual failure. This happened on my car - trust me - I know. [B]Q: Does the high cold pressure mean the head is definitely absolutely for sure cracked? [/B] A:Well, no, but it's about 99% likely. [B]Q: Does *no* cold pressure mean the head is OK? [/B] A: Yes, probably, but ONLY if the cooling system is tight and there is *zero* coolant loss. [B]Q: How do you know the head is cracked? I know a lot about other engines and I bet it's just a bad head gasket.[/B] A: That's great you know a lot about other engines. Now welcome to the world of the OM603. ;) A failed head gasket is not uncommon on a 60x but the symptoms are typically MUCH different - either mixed liquids (oil in coolant or vice-versa), or massive oil consumption & smoking when the gasket blows out into the timing chain cavity. The "high cold pressure" symptom will NOT be from a bad gasket. [B]Q: Rumor is the trap oxidizers contributed to the head cracking. Is that true?[/B] A: Nobody knows for sure, but there is a lot of circumstantial evidence pointing to the trap adding excessive heat load in the area of the exhaust ports, probably exacerbating the problem. This would be worse if the car was driven with the trap plugged, and/or the car came from a hot climate (central CA, Texas, Florida, etc.) [B]Q: Are the #17 and newer heads crack-proof?[/B] A: No, but they'll take a *lot* more abuse before cracking. I think I've heard of one or two that cracked after being severely overheated. [B]Q: How many cracked 603 heads do you know of?[/B] A: Well, this past year (2004), I think I heard of at least 6-8 total. Prior to that, probably 3-6 per year from 2000-2003? That's just from this forum and the MBZ.org email lists - who knows how many others are out there. [B]Q: What is the percentage of heads that have cracked and/or will crack?[/B] A: Unknown. My guess? Probably 20-40%. Maybe more. There are a LOT of people driving around, blissfully ignorant of the "high cold pressure" syndrome, until something bad happens like hydrolock or extreme erratic operating temps & overheating. [B]Q: What causes the cracked heads?[/B] A: You mean besides a flawed casting design? The main culprit seems to be overheating. That means a trip into the red zone (120C+) with a full cooling system. If you pop a radiator hose like I did, you can lose some coolant and have the head get steam pockets near the top of the water jacket, resulting very high localized temps, while the dash gauge temp sensor (which is lower) can be in liquid and only read ~115C. That's not a likely scenario but it happened to me. [B]Q: When did Mercedes figure this out, and how many variations are there?[/B] A: Apparently Mercedes changed the head design around 1988, right after the last 603.96x came to the USA. There are six different head casting numbers... 14, 15, 17, 18, 20, and 22. The head gasket design was also changed 5 times (six total part numbers). The #17 and newer heads are the crack-resistant heads. We're not sure about the #15, and that particular casting is as rare as a quiet night at home for Paris Hilton. :P [B]Q: So what temperature should a 603 run at?[/B] A: 99% of the time, it should be in the 80-100C range. End of story. Most common range is 85-95C. If it's in the 100-105C area (that's the remaining 1%!), it better be HOT outside, either idling in traffic or pulling up a grade, or otherwise under heavy load. When the load is removed, the temp should drop back under 100C quickly. If not, something is wrong. If it gets to [URL=http://www.W124performance.com/docs/mb/OM60X/OM603_high_temps.pdf]110C or higher[/URL], something is wrong. Period. Fix it! (Search other threads for the cooling system woes - that's a whole separate topic unto itself.) [B]Q: My head is OK for now, I think. What can I do to prevent cracking?[/B] A: Keep the cooling system in top shape and watch the temp gauge like a hawk, looking for the 80-100C range noted above. Replace the temp sender and the electric fan switch as a preventive measure if they are not recent. Keep the radiator & condenser fins cleaned out with compressed air or water. Use ONLY (!) Mercedes anti-freeze (or Zerex G-05) and replace it every 2-3 years. Replace the plastic [URL=http://www.meimann.com/images/mercedes/head_gasket/clean6.jpg]coolant reservoir tank[/URL] also, the new ones have a silica pack to control corrosion, and the old ones have a habit of cracking in the rear where you can't see the crack. A bottle of Water Wetter doesn't hurt either. [B]Q: My head is cracked. What will it cost (approximately) to replace it?[/B] A: As a DIY project with a used head, $1000-$1500 and 15-30 hours of your time for a novice. To pay a shop to do it with a used head, $2000-$2500 and 10-20 hours for a pro. For a new head, add $750-$1000 to those figures. [B]Q: How much does a new or used head cost?[/B] A: If you can find a used #17 head, they're typically $800-$1000, sometimes more. That usually includes valves & springs, but may not include prechambers, lifters or cam. A brand new (#22) head comes bare with no valves or springs, and current price is about $2000 list, $1600 wholesale. [B]Q: Are any modifications needed to bolt on the newer head?[/B] A: In general, no. However the newer heads all came with different (angled/inclined) prechambers and injectors, and our 1986/87 engines have vertical injection. That means your vertical prechambers may not seat properly, requiring [URL=http://www.meimann.com/images/mercedes/head_gasket/prechamber_mod2.jpg]modifications to the old prechambers[/URL] for them to seat properly. This only affects some newer heads, probably less than half - no way to tell until you get your replacement head, and do some measuring with the prechamber inserted. Yes, you can convert to the inclined/angled setup and elminate this problem. But that requires the newer prechambers, lock rings, injectors, AND glow plugs - then you need to bend the metal injection lines as well! Forget this option unless the used head includes all those parts. [B]Q: Should we just stay away from these cars (if they have the original #14 head)? [/B] A: Well, that depends how much you like them. I like them a LOT and I'm willing to spend the money on the head replacement. When it's done, you get one of the most incredible diesel cars Mercedes ever built. If these numbers are out of your budget, stick with the old/cheap OM617 models until you can afford to move up... you can get a whole 617 engine for less than a used 603 head. (And there's a reason for that, IMO! :P :P ) [B]Q: Is this at all related to the rod-bending 3.5L?[/B] A: No. The 3.5L (OM603.97x) engine, while sharing many of the 3.0L (OM603.96x) parts, had a design flaw in the connecting rods. Since this engine came out in the very late 80's and was imported to the USA in the S-class for 1990-95 models, it came with the improved #17 head. These engines are good donors for used heads. [i]OK - if there are any errors above, let me know and I'll correct them, or add to the list, etc... [/i] :sun_smile