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  #1  
Old 10-22-2004, 12:05 PM
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Question 87 300D Coolant issues

I have been searching and reading quite a few threads on the coolant and head failure issues on the 87 300 D, but now I have to ask about something that seems not to have been discussed in the past. If some one can direct me to a thread, that would be great.

I was looking in the coolant reservoire on my new 87 300D and noticed an oily sludge on the walls and cap. So I drained everything out of the system, took the res off and cleaned it out and did a cursory inspection of the hoses and the radiator insides (just ran my finger in around the hoses and where ever I could reach) and found no oil residue at all. It seems to be only in the reservoire which is original, I'm sure. Much of the rest of the system is newer including the water pump, radiator, hoses, etc. After cleaning the res I put it back on (wish I'd had a new one handy), filled the system with new coolant, the Zerex 05 as recommended here previously. However, I was in a bit of a panic thinking that the head was cracked which allowed the oil into the coolant. I took it to my very competent indy guy, who did a proper flush, overnight, testing of the coolant for gases, etc. and a pressure test. He came up with nothing. Neither did he find any coolant in the oil. This car has the original #14 head.

My indy says that in diesels, after years and years of blow by the coolant res will have accumulations of oil sometimes. Can this be true? Please confirm or refute. This car runs really well, and doesn't come close to overheating even with the a/c on at idle in 90+ temps. The upper rad hose is soft and pliable and pinchable in the morning when the car is cold.

This site is the best, and has already saved my some hard currency since I bought the car over a month ago. My first MB, and I love it.

Thanks.

DS
87 300 DT

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  #2  
Old 10-22-2004, 12:38 PM
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I wouldn't sweat it. Coolant reservoirs get cruddy looking over time, no matter the car. If the car doesn't overheat and overpressurize the cooling system, you are fine. There's no harm in cleaning out the coolant tank, but likely no benefit either.

- JimY
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  #3  
Old 10-22-2004, 04:08 PM
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I appreciate the advice. When I got the car, I hadn't been to this site. Then I started reading threads about the #14 heads cracking, and I thought, crap, there goes another 2 grand...

DS
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  #4  
Old 10-22-2004, 04:32 PM
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Like you, being still relatively new, I kept reading about the #14 head on the 603 and worried. Mine has no negative signs showing so I just watch the temperature gauge and the cooling system on a regular basis. I am about to flush and change though I'll be using the MB coolant I pre-purchased. I guess we should just maintain and drive them w/o allowing ourselves to worry. It it happens, then we would have to deal with it.
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Old 10-22-2004, 06:16 PM
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What you also need to watch

The main thing that will cause problems is the 212 switch which should turn on when coolant hits 100C on your temp guage. It is what causes the aux fan to come on which is what will cool the temp rapidly. I have been told that there are several different versions of this switch color coded to indicate at what temperature they cause the aux fan switch to activate. This switch should be tested regularly and the aux fan should be tested almost as ofter.
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  #6  
Old 10-22-2004, 06:31 PM
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Clean It

All cars do this - give it a bloody good clean - take the rad off and back flush it, put it back and fill with water. run for a bit, drain, repeat this until you can drink it, then refill with a/freeze and water. They can literally become silted up.
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  #7  
Old 10-22-2004, 08:17 PM
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Don't worry about the 14 head don't overheat it and you won't have a problem.
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  #8  
Old 10-22-2004, 09:20 PM
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There is some soluble oil in the coolant to lubricate the water pump. It's visible as small clear droplets most of the time, not many.

It will collect in the coolant tank, along with the slime that oxidized coolant makes as it ages.

You will also get some brownish black slop on the bottom if you never change the coolant, but you aren't going to do that, are you?

If not overheated, the #14 head seems to last a good long while, they didn't all crack.

Peter
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  #9  
Old 10-25-2004, 12:56 PM
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Thanks for the advice.

The aux fan switch, where is it located? I have never heard the fan come on yet. Though I haven't seen the temp go above 95 yet either.

DS
87 300D
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  #10  
Old 10-25-2004, 04:31 PM
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Aux fan switch where is it located?

location is the front of the engine topside at the coolant housing see attached pic. There are two plugs, one three pin keyed differently than the other two pin one so you can't get them swapped.
The color of the switch MB supplies for the '87 300D turbo almost aqua or turquoise blue actually, and it is a dual function switch. I have heard that these tend to fail rather frequently, mine did and the fan was stuck ON all the time, not as bad as if it failed open.
I figure sometime I will add a relay to carry the full load current, as I believe the switch contacts are a bit wimpy and not rated for lots of on/off cucles with the high starting current typical of the electrical fan used. Oh well, another MB product improvement, details will become available when I get 'round to it.
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87 300D Coolant issues-thermoswitch2.jpg  
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Last edited by dieseldiehard; 10-25-2004 at 04:40 PM.
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  #11  
Old 10-25-2004, 06:15 PM
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Thanks for that, I'll be checking it out as soon as I can. I suppose a new one is available from fastlane or the stealer?

DS
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  #12  
Old 10-26-2004, 04:57 PM
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I ordered mine from the stealer and it wasn't cheap, ran about $32 . Check with Fastlane though, perhaps they can get it at a discount. Sorry I can't find the box with the right p/n on it

I am planning to measure the current thru the switch, but am pretty sure its the full fan current and I would like to add a relay to carry that current to lighten up the load on this expensive part. MB does leave some room for imrovement.
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  #13  
Old 10-26-2004, 05:54 PM
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1) If the tank has black goo inside on the walls, it's possible the head or gasket at some point had leaked and allowed oil into the coolant. It's also possible for such a leak to be temporary and then stop (don't ask how I know). The tank should definitely be replaced as preventive maintenance after 15 years! The new tank is about $50, and is clear plastic (not yellow or brown), and has a silica pack inside to help control corrosion with the aluminum & iron parts in the system. Cheap insurance - trust me. (Photo below.) Monitor the coolant and make sure you're not getting black goo in the system, if so, the gasket is probably failed. Remember that mixed liquids is usualy a gasket, while high cold pressure (and/or erratic high temps) is often a cracked head. Passing a 20psi cooling system pressure test means absolutely nothing, other than the system doesn't have any gaping holes in it. :p

2) The 124/603 (603.960) came with a "blue" 105/128C temp switch that triggers the electric fan at 105C, and kills the AC compressor as a safety at a stupidly high 128C. The 126/603 (603.961) has a "gray" 105/120C switch that costs much less ($25, I think) and I like the lower temps as well. For some unknown reason, the 105C portion of the switch is almost always dead after 10+ years. At least it was on both of my 87's, my sister's, and a co-workers - 4 out of 4, seeing a pattern here? If it's not recent, replace it. Why? Lemme see, $30 for a new switch, $3000 for a new head. Hmmm... tough call.

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  #14  
Old 10-26-2004, 06:05 PM
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If I had known that the lower temp switch was available I would have ordered it instead. Say maybe I'll sell the blue switch on eBay and get myself the grey one
And thanks for the picture of an antiseptic engine again, Dave Always love looking them.
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  #15  
Old 10-26-2004, 06:09 PM
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4 out of 4, seeing a pattern here?

Statistic proof there is a design flaw here. I am really sure that an external relay will reduce that to one thermo switch in 30 years. I've gotta do some investigation on this subject . . .

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