Most likely your heater core is copper, or possibly aluminum.
I had a similar situation on a W126 (300SD) I once owned.
When I bought it the owner had just put a radiator on it within the =
year. When I inspected the coolant it was brown and rusty colored. =
Figuring that it just needed a good flush and a return to MB coolant, I =
removed it, flushed it and the cooling system, and installed the correct =
coolant. I would add that I also replaced hoses, as the hoses had a =
nasty accumulation of brown discoloration in them that I can only =
suspect was rust.
Within a matter of weeks I started having problems with the temperatures =
rising if the car was moving more than about 40-50 mph. As soon as I =
crossed that threshold, the temperature would climb a good 10-15 degrees =
above the proper 82F or thereabouts.
Anyway, I removed the radiator and took it to a trusted shop. The core =
was plugged in the very center but what they said was rust. Where it =
came from, I have no idea. When I flushed and refilled the system the =
coolant remained the proper honey color that MB coolant is.
Apparently the core was already clogged, but since I bought the car in =
the winter (relatively speaking) the problem didn't manifest itself =
until the ambient temps got up relatively high. I can only suspect that =
they were running straight water in the system, and it caused the block =
to rust, as it's the only part in the system that could do so.
Point being, flush the system for sure. Whether or not you'll continue =
to see the rust/crud in the system is questionable. I doubt it's your =
heater core.
Dan
> From: "Brian Toscano" <brian.tosc...@gmail.com>
>> Ernest,
>> I have thought the same thing. After I replaced the thermostat/flushed the
>> system I poured water in the upper radiator hose (connected to the
>> radiator) until water came out the thermostat housing. What I'm not clear
>> on is how does a heater core get rusty? Are they made of steel or iron and
>> not copper? Or does the rust from elsewhere just collect in the heater
>> core?
>>
>> I am somewhat concerned if the heater core is rusty and I try to clean it,
>> that it may spring a leak!
>>
>> My current plan is to leave the system as is for now and see how dirty the
>> coolant gets over the next 2-3 months. I suspect the hoses may continue to
>> shed rust/discolor the coolant. What I don't want to do is spend money on
>> something that will not solve the problem. If I'm going to get rust even
>> with new hoses, I don't see any reason to replace hoses that are otherwise
>> good.
>>
>> On Sat, Jun 2, 2012 at 5:32 PM, ernest breakfield <
>> erne...@backyardengineering.org> wrote:
>
>>> since your observation is that most of the crap is in the heater hoses,
>>> odds are that your cooling system isn't getting fully filled, and the air
>>> in the system is rising to the highest point (the heater core) and causing
>>> corrosion there.
>>> replacing the heater core in an XJ isn't fun.
>>>
>>> i'd suggest rinsing the heater core thoroughly, but hooking up the
>>> garden hose to the inlets on the heater core and letting is run 'til it's
>>> clear, then hooking the hose up to the other side. repeat until fully clear.
>>> then read up on how to get the system completely full ('burped') by
>>> filling at the radiator hose, and see if you still have the same problem.
>>> cheers!
>>> e
>>> '85 300D (200K+)
>>> '94 XJ (240K+)
>>>
>>> On 02/Jun/12 10:51, Brian Toscano wrote:
>>>> Last night I drained the coolant from the drain plug on the radiator.
>>>> What
>>>> came out first was bright green. After a little bit, it turns rusty
>>>> brown,
>>>> and then turned to dirty coolant. This was just draining. Likewise, what
>>>> is in the expansion tank is typically rust colored and when I poured clean
>>>> water into the heater core, what came out was rust colored. What I
>>>> removed
>>>> the water pump what I saw was dirty coolant, but the inside of the engine
>>>> (outside of the cylinder wall for #1) looks perfectly fine and rust-free.
>>>> It makes me think the coolant does separate as it cools.
>>>>
>>>> The water pump itself looks fine also. A gasket leak developed on the top
>>>> of the pump after I did the first round of flushing.
>>>>
>>>> What has the most crap buildup are the heater hoses. The supply and
>>>> return to the heater core have a rust buildup inside. The lower radiator
>>>> hose has a large spring in it almost the entire length and that spring
>>>> holds a ton of crap. It makes me wonder where all this rust comes from if
>>>> the inside of the engine looks fine.
>>>>
>>>> On Mon, May 28, 2012 at 8:39 AM, Brian
>>>> Toscano<brian.toscano@gmail.**com<brian.tosc...@gmail.com>
>>>> >wrote:
>>>>
>>>> I considered that the dark radiator has an effect on the coolant. The
>>>>> bright green when in the radiator is almost clear in a coolant tester.
>>>>> However, what's in the expansion tank is darker. The original problem
>>>>> has
>>>>> been fixed. The flushing I did definitely helped. I'm not expecting
>>>>> 100%
>>>>> perfectly new looking coolant in 11 year old engine with cast iron block
>>>>> and head.
>>>>>
>>>>>
>>>>> On Sun, May 27, 2012 at 9:26 PM, Max<meadedil...@bellsouth.net> wrote:
>>>>>
>>>>> Remove a sample from the radiator and another from expansion tank to
>>>>>> compare side by side; it's awfully hard to judge color inside a dark
>>>>>> radiator.
>>>>>>
>>>>>> Did you fix the original problem?
>>>>>>
>>>>>> I think your flushing method failed.
>>>>>> --
>>>>>> Max Dillon
>>>>>> Charleston SC
>>>>>> '95 E300, '87 300TD
>
>
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