87 300SDL cracked head? - PeachParts Mercedes-Benz Forum

Smokey · #1 12-07-2002, 07:11 PM

I'm looking a an 87 300 SDL with 78k miles on it. Only 11k miles were put on it through 97 and it runs great. The owner said that the turbo was "gunked" up when he bought it and he had it "cleaned up/ fixed".

Visually everything looks OK but from all of you out there who have had head problems or are aware of the potential problems with cracked heads, is there anything I should look or test for with this car to minimize my risk?

#2 12-07-2002, 08:42 PM

If there is no white smoke, un explained overheating or oil in your coolant, then your head is fine. I have the original head on my 87.. seems 86 had more problems with that than 87.

BJ300SDL · #3 12-08-2002, 09:05 AM

78k!! That thing is just getting "broken" in!! Is it in nice shape?

Ken300D · #4 12-08-2002, 12:46 PM

The area around the turbo that can get "gunked up" is actually after the turbo in the intake air stream path. From the EGR valve all through the intake crossover pipe (on top of the engine) and all through the intake manifold that goes to each cylinder.

This is because the EGR valve spews exhaust soot into the intake, and to make matters worse, oily crankcase blowby is vented into the intake airstream as well. (Crankcase blowby is vented into the airstream before the turbo.) Most people find a way to conveniently have the EGR valve "malfunction" on these cars. If the vacuum line to it should become accidently disconnected and plugged, the EGR valve will "malfunction" and stop blowing soot into the intake.

It's kinda like fatty deposits in blood vessels - it can reduce the air flow. I've seen pictures where the air passageway right at the EGR valve was more than half blocked.

A cracked head can cause a limited number of things to happen:

1) Water in oil. Shows up as white frothy foam on the dipstick.
2) Oil in water. Shows up as oily drops in the coolant.
3) Coolant in combustion chamber. White smoke.
4) Exhaust gas in coolant. Overheating and bubbles/air overpressure in radiator or overflow tank.
5) Oil in combustion chamber. Oil smoke.
6) Exhaust gas in oil/crankcase. Excessive blowby.

Now the probability of any of these six happening is impacted by the design of the head - that is, where the cracks are likely to occur and what passageways are involved.

Those more familiar with your engine and cracked heads can tell you more, but I think # 1, #2, # 3, and # 4 are the most likely.

Of these, probably # 2 and # 4 are more likely.

Some of these are also cause by a blown head gasket too.

It sounds like you got a really nice car. I think everyone with that engine emphasizes not to let it EVER overheat - that can crack the aluminum head.

Ken300D

Smokey · #5 12-08-2002, 09:17 PM

Thanks for the feedback! The 300SDL is in great shape! I'll try to take some pics and get them up after I take ownership. Thanks Ken for the tips on what to look for related to potential problems and where exhaust gunk collects.

I'll let you know how the inspection turns out.

John

lrg · #6 12-08-2002, 11:47 PM

One sure sign of a cracked head is if the radiator hoses are really hard even after the engine has cooled off. They should be pretty hard when the engine is hot but should be squishy after it cools and the pressure relaxes. If it stays hard then you are likely getting pressure into the cooling system from cracks in the head.

goldenbear · #7 12-09-2002, 02:03 PM

Smokey,

Not to scare you off, as this may not be the case with you, but I purchased my "cream puff" in 02/2000. Nine months later it began having symptoms of a leaking head gasket. The head was fine, but the head gasket was a decent expense item. I put >$10k into the car in 2001. Granted, the majority of the work was performed at my dealer, but I have a good relationship with them and did not have an indy at the time. I would like to share my complete maintenance history, but do not currently have access to a server.

I attribute the majority, if not all, of the non-standard / early maintenance items to the fact that the vehicle was driven very infrequently. I love the car and it runs like new. I am confident it will for many years / miles.

sixto · #8 12-09-2002, 02:54 PM

My 87 specifically had cracks in the head between the combustion chamber and the water jackets in the #4 cylinder. Cracks were starting to form in other cylinders but compression was good in all but #4.

Lots of compressed air in the cooling system was the giveaway. No oil in the coolant or coolant in the oil but the machine shop guy said that the head gasket was on its way out.

If you're a decent wrench, don't let potential head problems scare you away from an 86-87 SDL. You can get yourself back on the road for about the cost of a good transmission rebuild. Plus guys like gsxr and lrg are here to guide you along the way.

Sixto
91 300SE
87 300SDL
83 300SD

gsxr · #9 12-09-2002, 03:48 PM

I had the same thing. The symptom was high pressure in the cooling system with the engine stone cold, after sitting overnight. The oil & coolant were clean, no bubbles or odor in the coolant tank. Drive the car hard, park it for 12+ hours, squeeze the upper hose. It should pinch together easily with 2 fingers. If it's so tight you can't pinch it at all, there MAY be a head or gasket problem. I had cracks in cylinders 1, 5, and 6 (I think). It's not a fun - or cheap - job, but it's not impossible. Photos of my fiasco... um, I mean project are here:

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

BTW - the 1987 models had MORE trouble because they got the evil Trap Oxidizer (free recall to remove). The 1986 models were usually OK. Watch the temp gauge closely, it should be 80-100C at almost all times. If it ever goes above 105C there IS a problem that must be fixed (usually fan clutch or radiator). Damage should not occur until 115-120C or beyond. My cars, with new cooling systems, won't get over 100-105C, ever - even in 100-110F ambient temps.

HTH,

sixto · #10 12-09-2002, 04:57 PM

I might have some investigating to do. My SDL gauge can get to 95C while idling in Palo Alto, CA in December with no AC. Drops to 85C as soon as it's moving.

Sixto
91 300SE
87 300SDL
83 300SD

gsxr · #11 12-09-2002, 05:10 PM

sixto, I wouldn't worry too much. With my new head and new temp sender, my car spends almost all of it's time between 90-95C. It almost never goes above or below that range, even when cold out (around 30F). If you see 105C+, especially in cool weather with no AC, then you can start worrying! Until then you might be chasing your tail... BT, DT!