87 300D Coolant Change Question - PeachParts Mercedes-Benz Forum

Jmana · #1 07-04-2006, 11:48 PM

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.

Hatterasguy · #2 07-05-2006, 12:00 AM

I just drain the radiator, and refill it with water a few times. You can also use a flush if you want as well.

I don't want to mess with the block drains since by the looks of mine they will not only be a battle to remove, but make a nice mess in the process. You seem to be able to drain most of the system just from the radiator, plus if you do it every two years leaving a couple of quarts of the old stuff in their really isn't a problem.

Jmana · #3 07-05-2006, 12:05 AM

Would using a flush be a bad idea on this car, since it could potentially cause chunks of scale to come loose?

Hatterasguy · #4 07-05-2006, 12:18 AM

Pull one of the radiator hoses off and see what it looks like inside. If its pretty clean I don't see how a flush will hurt you. My cooling system is only 2 years old, but I am going to run some Prestone flush through mostly for the heck of it.

One thing that you should do is remove the radiator and clean the fins. They become clogged with crap and cooling is grealty affected.

dieseldiehard · #5 07-05-2006, 02:24 AM

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!

Quote:

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.

Jmana · #6 07-05-2006, 06:40 AM

Thanks for the info, it sounds like an acid flush is the way to go. By the way, when it almost overheated, the dial was at the white line which is just below the red line, right around 120 degrees. Once we replaced the aux fan fuse, it cooled down to about 90. The AC was running the whole time. The owner said he never had it go above 90, but he rarely drove it, and when he did it was on the highway. When I test drove it I took it around town and drove it kind of hard to make sure there weren't any existing problems.