Head gasket missed the bullet I think - PeachParts Mercedes-Benz Forum

virtualdoc07 · #1 02-18-2004, 07:18 PM

Well, the weak sister of my stable, Silver 1986 SDL, just came back yesterday. What I thought was a cracked head was really a bad head gasket. While in there I replaced the valve lifters also. Total ocst $2k, which seems high from a an independent repair shop. Should I feel good about not having to buy a head?...Or did I get ripped off?

Brad123D · #2 02-18-2004, 08:57 PM

Did they check the Head/Block parting surface to see if it was within spec's (Straight)? SOMETHING caused the headgasket to fail.

md21722 · #3 02-19-2004, 12:41 PM

That sounds like it cost too much. Did you go to Woods or something???

virtualdoc07 · #4 02-19-2004, 01:19 PM

Wursters The kid is running it now and tries hard, but I find Erol's to be best in town, howver a PITA to get over there from Brentwood. Next Time I'll use Erols again.

gsxr · #5 02-19-2004, 02:59 PM

Seems a little high, but not outrageous. The job is roughly 15 hours labor plus $3-500 in parts (with new lifters). Problem is, if the head cracks in the future, it's the same ~$2k in parts & labor all over again but this time PLUS another ~$1k for a used head or $2k for a new one!

IMO, if the head must come off a 603 for whatever reason, I definitely recommend replacing the head with a used 3.5L head (which is the improved version). They're not that expensive, really. If the old head wasn't cracked, great, sell it on eBay and recover some (most?) of the cost of the improved "#17" used head. I have very little faith in the original "#14" heads, I expect they will all crack eventually, and if you have an excuse to replace one it's a good idea. Anyway just keep an eye on the engine temps, keep them under ~100C and it should be fine.

shane83SD · #6 02-20-2004, 01:23 AM

Hi GSXR,

I'm curious regarding the specific improvements made for 350 heads. Thermo cycles on two different metal will create stress and perhaps wear on the interface. I also understand that the diesel engine run at much higher stress than the gasser. Why 350 head will not prone to failure? Can it last as long as the iron head SDs (on average)?

gsxr · #7 02-20-2004, 11:44 AM

The changes to the 3.5L head (and gaskets) are detailed in the factory OM603 engine manual. Basically, they increased the thickness of the metal for the jackets surrounding the exhaust valves, IIRC...? There were a couple of other changes also. The newer heads (#20, and #23?) also made changes to the oil passage ahead of the #1 cylinder, and a couple of other things too. Even with the changes they're not as indestructible as the old iron head beasts, but they're much better. The original 603 head (#14) was the really weak one. They can last a loooong time if they are *never* overheated or thermally stressed, but you need to watch the temp gauge closely.

shane83SD · #8 02-20-2004, 10:58 PM

Hi GXSR,

Thanks for the info. Makes sense to beef up the exhaust port. Had a personal experience with a steamming Bimmer, hair line crack between exhaust port and coolant passage. Major white smoke. The plastic radiator may cause many cracked heads. Talk about a deadly combination!!!

Is the MB radiator in SDL also plastic (top part & neck)? Where can one find all metal radiator?

gsxr · #9 02-21-2004, 01:39 AM

Most Mercedes after about 1980 had plastic radiator tanks. They seem to last a long time as long as you use Mercedes antifreeze (or Zerex G-05), and change it every 2-3 years maximum. The "green" stuff - or anything else - isn't chemically buffered enough to handle the pH changes and the plastic gets brittle over time if you use the wrong coolant. Waaaay too many people (mechanics included!) don't know this and think all antifreeze is the same, so why pay $10/gal for MB a/f when the "green stuff" costs half that? It ends up being a costly mistake after a $300 radiator failure (and/or $3k head replacement!)