anyone with head-cracking experience? 300SDL - PeachParts Mercedes-Benz Forum

GregS · #1 01-16-2003, 10:13 AM

When shopping for an SDL, I'm just wondering how I can gauge the potential that a car might have (or will have) a cracked head? Is it an age related thing, a frequency-of-coolant-change thing, or is it just totally random? Was the head cracking something that happened early on in the cars life and would be fixed by now (i.e., random heads were cast poorly, or had some other manufacturing defect)?

It seems to me that a lot of people "have heard" that these cars can crack heads, but I have only heard ONE person on this board say that they have personally experienced the problem.

Lastly, do these cars have the B2 piston issue, or was that only on the gas V8s? Are the transmission in these cars as good as those put in the w123 300D?

Thanks,

Greg
'84 300D, 172k

rwthomas1 · #2 01-16-2003, 10:52 AM

A pre-purchase inspection is the best option. A compression/leakdown test, test for oil in coolant, coolant in oil, etc. While this is still no guarantee it is better than winging it. Evidence of regular service and care goes a long way to making me believe a car was not abused. If its the original owner I like to simply ask them. If you are able to read people well likely you will know if he is lying or not. RT

samiam4 · #3 01-16-2003, 11:44 AM

Dave,

I don't think it will show up in a compression test or a leak down- but they are PPI things to do to ensure a healthy engine.

I know of someone whom has experienced this. He drove his till on one or two occasions he hot started the car and it acted like a mechanical lock. The head is kinda pot luck. Reported highway cars are less likely to have the problem.

I assue the Trapoxidizer has been removed correct?

Michael

#4 01-16-2003, 02:32 PM

Also get an 87, from what I have seen the 86's had more problems with a cracking head.

The transmissions in the 300SDL's IMO are even better than that in the 123 and older 126, they are nearly bulletproof.

samiam4 · #5 01-16-2003, 03:20 PM

Üí Turbodiesel,

Are you sure? I have always heard the EXACT opposite. In fact, Dave Quary( of asap), said he never saw a good 87' cylinderhead, but all 1986 core motors had good heads. I know MB revised cylinder headgaskets many times. Maybe you've seen headgasket leakage-not cracked heads?? I also was under the impression that 1986's didn't have trap oxidizers which is given much of the credit for cracking the heads (creating extra stress due to heat buildup).

Michael

gsxr · #6 01-16-2003, 08:44 PM

Michael is correct, the 1986 is preferred for the reasons stated. It is hard to spot a minor crack, as the oil & water rarely mix, and testing for exhaust in the cooling system may or may not work (it's REALLY slight and needs to be under load).

The only "early symptom" that I know of for the cracked head (or failing gasket) is high pressure in the cooling system when cold (this assumes you have a GOOD radiator cap and thermostat). Remove the cap when cold, reinstall. Drive the car hard for a day with several full-throttle runs to 60-70mph. Let it sit overnight and cool completely. The next morning, pinch the upper radiator hose. It should be fairly soft, with either low pressure, no pressure, or even a slight vacuum. If it is SO tight you can't squeeze it (i.e., high pressure, 10-20psi) then there is DEFINITELY something wrong with the head or gasket. You may be able to drive for thousands of miles like that, you may not. Depends on the damage. Also, you may have ZERO coolant loss... just because your coolant is clean & full does NOT mean the car is OK.

I know this because I experienced it on my car personally, and have talked to numerous others with similar problems. One ignored the "high cold pressure" until one day his engine hydrolocked, as the crack opened up enough to allow coolant to enter a cylinder. Cost for a replacement head will vary between $1000-$4000, depending if you get new or used (only the 3.5 heads are good used), and if you do the work yourself or pay a shop. Photos of my R&R are here:

http://www.meimann.com/images/mercedes/head_gasket/

Best regards,

psfred · #7 01-16-2003, 10:55 PM

I've heard the newer heads are considerably less prone to cracking, and there are two failure modes on the older ones -- instant crack from overheating (if the temp gauge goes into the red, it's gonna crack) and minor cracks that appear in normal service and gradually get worse and worse.

Oil in the coolant and cold pressure can also be from a bad head gasket, although cold pressure in the cooling system is rather unlikely from a bad head gasket.

Peter

PaulH · #8 01-16-2003, 11:22 PM

I have an "87 300SDL and it is fine. I have done the "squeeze" test as stated. I worry about it, but, on the other hand, I have a friend who has over 300,000 miles on his '87 603 engine and hasn't had a problem. He uses dino oil changed every 3000 miles and sits in HOT Wash D.C. traffic every summer just like I do. Everything that I've heard and read suggests that if it hasn't been in the red zone of the temp. gauge, it should be OK. And IF you believe the owner's book that states that high temps are OK as long as it doesn't hit the red zone, then you can sleep at night. (Remember, I said "IF") My friend is a mechanic and tells me to stop worrying about it and run the car hard as long as you change the oil often and don't overheat it. Have a good day.

sixto · #9 01-16-2003, 11:26 PM

If you check the archives, there might be a list of the succession of 603 head part numbers. I think it's only the 7th and 8th digits that changed with the updates, something like 01 -> xx -> xx -> 17. If a car you're looking at has the latest head part number, you should have... well... marginally less to fear.

As has been posted in the past, a 300SDL is a great car even if you have to spend $3000 for a new head somewhere down the road.

I'm going for a drive now for the heck of it

Sixto
91 300SE
87 300SDL
83 300SD

gsxr · #10 01-17-2003, 01:08 AM

To add to psfred & sixto, yes the new redesigned heads are MUCH less crack prone. Mercedes actually redesigned the heads 3 times (4 part numbers) and the gaskets 5 times (6 part numbers). The latest head design was completed in the late 80's, and was used on all 1990-up 3.5L engines. It has much thicker castings in certain areas, which are specified in the OM603 engine manual. So if you can find a good 3.5L head used, it will work fine and not crack. To date, I have not heard of a SINGLE redesigned head failing under normal use. The price for a new, bare head has gone up in the last year, I paid $1295 for mine in Jan-2002 and now they are at LEAST $1495. That's guides only, no valves, cam, or lifters...

Not trying to scare anyone, just trying to edumacate those interested in 603's. Personally I think the 603 is a fantastic engine and is worth replacing the head on if it ever fails. Zero to sixty in 10.x seconds, 30-34mpg on the freeway, and typical life of 500kmi... what's not to like?

(The older iron-head beasts were indestructible, but got worse MPG, were slower, and WAY less refined - no manners at all!)

Regards,

#11 01-17-2003, 03:48 AM

My uncles '86 SDL got it's head replaced at some point, and currently it only has 170,000 miles. My '87 with 300k has the original head with no known issues..

I have ALWAYS heard the '86's are the worst with heads.

GregS · #12 01-17-2003, 10:13 AM

O.K. guys, so what's the part numer that I am to look for. The car I want to look at supposedly just had the head and head gasket replaced, so I would love to know if it has the updated number on it. Supposing it doesn't have the new number, I can assume the shop just rebuilt a used head from a junk car - this would not be good as I would still be risking a cracked head. The dealer which is selling the car also supposedly replaced the head, but the salesman couldn't tell me much. I'll check the car out and get a feel for these people. If they seem shady then I'll just walk.

Although it will be hard to walk from my dreamcar - a black on black 300sdl.

Greg
'84 300D, 172k

surfblau · #13 01-17-2003, 02:01 PM

My 87SDL had a seriously cracked head. The cause was probably related to the trap oxidizer. At any rate, the car became undrivable, the PO took it to the used MB shop that she bought it from, and they took it back and sold her another luxury car of some sort.

They put a new head it the returned car and sold it to me.

One year later, it drives better and better every day.

alec

samiam4 · #14 01-17-2003, 11:54 PM

Right,

You've reminded me- Tom's car had a new radiator when he purchased it. About a year later, it got the new cylinder head=0)

Michael

gsxr · #15 01-18-2003, 01:55 AM

OK, here's the part numbers for the new & old heads. This is the number cast into the head, around the number 2 & 3 cylinder area. It is NOT the number you order from the dealer, and don't ask me why they don't match, I dunno:

603-016-14-01 - The old, original 1986-87 head
603-016-22-01 - The newest version of the head

I don't know what the numbers in between are. Maybe if someone has a 3.5L engine (1990-1995) with the original head, they could tell us the number cast into it...? Anyway, this should help someone looking at cars to buy. If the head is a "14" it is original. If the number is between 14 and 22, who knows what it is. If it's a "22" it's a NEW, good head!

Regards,