How hot is "almost overheat"? I believe the heads crack from lack of flushes, scale builds up in the radiator and even with the fans (engine and AC fan) working the 603 will run hot. Also the Nasty Trap Oxidizer aggravated many a head failure, people don't take that in to account! Before lots of them were replaced the engines would choke on the exhaust gasses built up when the traps plugged and the engines ran much hotter as a result.
Your radiator may have scale in areas where there is blockage, it usually happens that way (not evenly) and an acidic flush is recommendable if its an old radiator. An IR thermo device may show if there is uneven cooling.
Personally I would just replace the radiator if its original. A 603 should run cool (well, relatively cool but hotter than a 617 turbodiesel) if everything is proper.
The scale comes out mostly in solution, it dissolves and won't plug anything.
The block drain is easy to get to, its a valve on the Rt side just back of the turbo. MB should have put that type of valve on earlier chassis, it makes draining the block and flushing easy. You can fit a hose over the nipple and turn the body and it opens up to allow draining into a bucket or whatever. The hex nut on 617's is a real PITA to open the first time, as MB sealed them tight with the block paint or something. In a few cars I've tried using a 5 ft extension on a hex tool to no avail. Then you need heat (blue wrench)!
Give me a 603 cooling system to flush anyday! Amd MB coolant is cheap insurance. $20 for two years isn't all that bad!
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Originally Posted by Jmana
From what I have read so far about the 87 300D's original head problems, is that it seems to be caused from either not using the proper antifreeze, or else not changing it frequently enough. The one I just bought has the correct antifreeze in it, but I don't know how old it is, so one of the first things I want to do is change the thermostat and flush out the system. My concern is how do I flush the system out, without causing scale and such to come off and potentially clog up the coolant passages? The head seems to be ok, I checked the oil (which hasn't been changed for 3 months) and it didn't show any contamination, and the exhaust is clear. The car did almost overheat on a test drive, but found the aux fan fuse had blown. So I want to do the coolant change the proper way to try and extend the life of this head.
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