Can anyone tell me the reliability record of the six cylinder 3.0 engine?Is it as good as the five cylinder?

i am a newbie, so take this with a grain of salt. what i have observed here is no, in general the perception is that the six is not as reliable as the five. reason seems to be that the six has an aluminum head. the five, a cast iron. any hint of overheating on the six can lead to failure of the head. the csat iron head found on the five is more robust. or that at least is the comon thought here. i own an 86sdl with almost 200k showing on the odometer. so far so good. all i know and then some.

Djoyce92,

I have an '87 300SDL which I acquired last September and have asked the same question. From my understanding of what I've read, the heads on these engines may be problematic. I've seen alot of these engines go to 250K with no problems and others have had problems. No problems with mine so far, (knock on wood). I know that if you overheat these cars, you are in for a new head soon.

I've also read that MB has redesigned the heads for these engines but I don't know the details what they did to redesign them; one must conclude that maybe they are more robust in some areas of the head.

I do know that these cars have problems with leaking head gaskets and you may see oil leakage around the front or rear of the engine, which may be common for this car. In fact, I have noticed a small around of leakeage around the rear of the engine where the head gasket is located. It is a small leak and it drips oil onto the garage floor about the size of a dime every time it is driven but that's about it....I have learned to live with that small leakage but I wish I could stop it with something other than replacing the head gasket....maybe I may try some JB Weld.

The trap oxidizer should have already been removed on these cars. If not, MB will do the conversion for free.

Other than that, these engines are the smoothest running diesels I know of. In fact, it is hard to tell you are in a diesel when you are at a stop light when compared to my 240D. I am amazed at the power this engine produces; it feels like you are in a turbocharged V-8.


Herb
'87 300SDL
'82 240D

I have an 87 300SDL and just went through the dreaded head work you speak of.

At around 235k miles, I took the car in for (more or less) a jumpy temp gauge and a gradual loss of cooant. After replacing the Aux water pump and thermostat, they sent me on my way. The car overheated about 15 miles out of town. I took it back and they found the expansion tank would hold pressure forever. A LOT of pressure.

When I mentioned these symptoms here on the forums, everyone knew what I had in store...

about 10 weeks of waiting (long story...BAD dealer), 36 hours labor, and $5200 later, the car runs like a champ. I had a new head, valves, gaskets, etc put in.

Knock on wood, but I am now approaching 255k miles and no problems to speak of.

Good luck.

__________________
Lance Allison
Lance@LanceAllison.com

Current:
11 MB S550 4Matic, 55k miles, Designo Black/Black
14 Ford F150 XLT Lariat Crew, 73k miles, 5.0
Coyote V8 4x4. Black/tan.
09 GMC Envoy Denali, 5.3 V8, 4x4 SWB. 38k miles,
Jewel Red/Med Gray.

Gone:
87 MB 300SDL, 320k miles, Astral Silver/Blue.
98 VW Jetta TDI, 488k miles, Classic Green/Gray.
85 Olds 98 Brougham FWD, 4.3 DIESEL V6, 80k
miles, 3x Gray.

MBCA Member, Chicago Region

Wow, $5200?! That seems a bit excessive for just a new head!

Yep, that's what I thought, too.
The aux pump they replaced was $400 parts and labor...
The head work was $2500 for parts and 36 (YES, THIRTY-SIX hours labor).

I'm still not convinced there was coolant in the car when I picked it up from the aux pump job....

__________________
Lance Allison
Lance@LanceAllison.com

Current:
11 MB S550 4Matic, 55k miles, Designo Black/Black
14 Ford F150 XLT Lariat Crew, 73k miles, 5.0
Coyote V8 4x4. Black/tan.
09 GMC Envoy Denali, 5.3 V8, 4x4 SWB. 38k miles,
Jewel Red/Med Gray.

Gone:
87 MB 300SDL, 320k miles, Astral Silver/Blue.
98 VW Jetta TDI, 488k miles, Classic Green/Gray.
85 Olds 98 Brougham FWD, 4.3 DIESEL V6, 80k
miles, 3x Gray.

MBCA Member, Chicago Region

The only serious problems are leaking head gaskets and cracked heads. Some heads crack without being overheated, but most are done in by coolant loss or a bad radiator -- either it plugs up and overheats the engine or the hose nipple breaks off.

The leak at the rear of the head can sometimes be fixed by re-tightening the headbolts back there. Otherwise, new gasket.

There is a LOT of labor in replacing the head on this car for some reason. I've not investigated, but it seems to be much more work than on a 617. I'd jump for the gasket rather than blow the head from overheating.

The head is something like $1800 on fastlane, and that is bare, no cam, tappets, or valves. Will be more at a dealer. Labor on the head should be 12 hours, I think -- only takes 50 to do a complete engine!

The W126 chassis is marvelous.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Peter,

Is it common to try retightening the head first? I would figure that if the head bolts turn below the torque setting, then I think it would be OK to turn these bolts but turning the head bolts beyond the torque specification would have me wondering if one may crack the head in doing so or doing other damage like warping.

Herb

'87 300SDL
'82 240D

Herb:

These are stretch bolts -- tighten to a specified torque, then an additional angular rotation, usually 90 or 180 degrees.

What happens is that the aluminum gives a little, and the head gasket looses it's seal on the oil passage. Pulling down on the bolts will re-seal the oil passage.

I've seen mention that the Elring head gasket isn't as good and the other suppliers for this particular application -- the sealing material around the oil passage holes doesn't hold up well.

Certainly I would only try tightening the head bolts ONCE -- they will continue to turn (at higher and higher torque) until the threads pull out of the block or the bolt fails. Both are bad!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!