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Discussion Starter #1
Winter maintenance continues to throw up surprises :laugh

Found that my ventilation system was still putting out warm air even though it was set to cool. This let me to suspect the valve and I pulled the pipes that feed the unit to check - to my surprise the water that spilled out was black :eek

When I serviced the radiator some years ago, the coolant was the typical rust colour - no antifreeze as far as I could tell. So, I flushed the system and filled it with pre-mixed green antifreeze. Paid no attention to it till today.

Soooo, decided to flush the system - which took a while. Then I squeezed the top radiator hose which crackled noticably ! Mmmm - took it off and found it had a lot of scale inside - that was not the case when I first serviced the radiator. I cleaned the hose and what came out was like coffee-grounds. It is somewhat magnetic, but it has that black look to it which I have found on some rusted mog steels ! That dark blue/black look.

There was no scale on the inside of the alluminium thermostat housing, nor on the inside of thge brass radiator inlet - it seems to like rubber ! The rubber cleaned OK and looks fine - shiny and not deteriorated in any way.

To eliminate any cracked head issues, I did a bubble test on the system and it checks out fine.

Anybody has any ideas/explanation ? Seen it before ?
 

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I am pretty familiar with that stuff, assuming it is hard gritty stuff - it is the scourge of all Jaguar V12 engines. I fitted Tefba filters in the top radiator hose, they filter out all the junk from the cooling system. No matter how many time I flushed it, changed the coolant etc, I would always have some particles like that in the filters and would have the radiator rodded every second year and it would be 20% blocked at least, but it was a very fine radiator.

The black things are the Tefba filters. ( This is a friend XJ-S)




I suspect that it comes from the block, and is something chemical in nature, rather than corrosion. If that was in your cooling system, I would check the radiator, as it would be pretty easy to block the tubes given the amount of stuff you have found so far.

If your radiator is blocked, get one of these, because it will continue to come out of the block for a long time, and it is a lot cheaper than getting the radiator rodded. If it is not blocked, the the tubes are big enough to let the stuff pass through, but seem like the heater matrix is a bit finer. Chances are the crud also stops the heater valve from closing, or the control wire is bent.

http://www.ebay.com.au/itm/Radiator-Coolant-Filter-suits-50mm-2-Hose-Sent-by-Registered-Post-/111391876989 Check it once a week until you are not getting any more material coming out.
 

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Discussion Starter #3
I suspect you are correct Ian. I also do not believe in coincidence - I suspect the anti-freeze I put in had something to do with it. Who knows what chemical additives were in there !
I am going to try and get things cleaned out and when satisfied go with a known brand of anti-freeze.
 

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Valvoline Zerex G 05 is highly recommended.

Check near the bottom of this chart:

https://bevo.mercedes-benz.com/bevolisten/325.0_en.html

I've used that (Premix and straight up for mixing if I can find it, no sense in paying for distilled water if I don't have to) in all my mogs without issue. Thats from -43C (not starting, too cold for old rubber and such) to +34C, running, but a wee bit warm in the sun without A/C ;)
 

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Discussion Starter #5 (Edited)
Last night - after a few glasses of good red I might add - I had a thought. If it is chemical, it is likely some sort of electrolysis (battery action) action is involved. Then I also realised that the radiator is actually electrically isolated from the rest of the cab. Went out this morning and did a quick measurement- sure enough, radiator is isolated and there is a 200mV potential with a 20uA current. May not seem like much, but given that the coolant is fresh and it is cold outside, I reckon it is indeed significant. I will do a measurement later today once things have warmed up and I have run the engine a bit.

Now I have to think about what to do about it - providing an earthing strap to the radiator might sort it - but does it simply shift to another problem ???? Food for thought.
 

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...Now I have to think about what to do about it - providing an earthing strap to the radiator might sort it - but does it simply shift to another problem ???? Food for thought.
Indeed. The question is why do you have a different ground potential there?

First thing I would do is to disconnect all batteries. So there should be no external voltage and current available. Then short the grounds for some time to get any potential difference away.

Check next day if another potential has build up. Then your cooling system IS a battery.

If not the current has to come from somewhere and may create some chemical reaction. Quite far side but possible. So look for anything attached to the radiator and check the current and voltage until you find the culprit.

mysterious.

Mike
 

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Discussion Starter #7 (Edited)
There is a lot of advice from reputable sources regarding electrolysis and corrosion - both the marine and automotive worlds have been battling this issue. In my case, grounding the radiator will actually make it worse it would seem.

Mike's advice is inline with the automotive advice given by many. I have determined that in my case, there is no stray current due to bad earths and the cooling system itself is acting like a battery. The reason for this is that the old coolant acts like an electrolyte. To prevent this, it is necessary to use only distilled water and a good anti-freeze. This is where I am heading. The water used must be de-mineralised and have a neutral PH. Many recommend that the coolant be tested for PH on a regular basis and if it is not neutral (7) it be replaced with fresh coolant. It is apparently normal for the coolant to wear out chemically as it is doing its job over time.

As a endnote - the Mog actually has two radiators - the big black thing in the front that is made of copper/brass. And then a the tiny shiny thing hidden inside the dash that is made of aluminium. So if you think your old mog does not sport an Alu radiator - think again !!!!



Cleaning the system requires a chelating agent - this is what citric acid is and what MB recommends be used. A chelating agent removes any heavy metals that is free withing the system.

Thats it in a nutshell.

In looking for stray currents, I also had a hard time finding where the cab is getting its earth from. It would seem that it s through the harness only. This seems like problem to me given that the harness connectors at the bulkhead is a weakpoint. Can anybody tell me if I had perhaps missed the ground strap between the cab and the chassis/battery ? Perhaps there should be one and mine was made to disappear by a PO !!!
 

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Discussion Starter #9
Coolant vent line

Well, the surprises keep popping up - years of neglect no doubt !

As I was flushing the system, I found it curious the system would not fill properly until the thermostat opens. Turns out the vent line was blocked - item 5 in pic. Flow is purposely restricted by a small hole in the plastic expansion tank inlet. It is only 2mm big, so easily blocked.
 

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Discussion Starter #10
Cab Ground

OK, so I have looked through the electrical drawing and there are only 2 earths.
Pic 1 shows them circled.
I have found the heavy duty one - arrow in pic2.
But where is the first one ? it is a very thin wire so not much of a ground.
Unless I find something else, I reckon a decent ground wire between cab and chassis will be my next modification !
 

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Kiwi, Iain priced up the Evans waterless coolant the other week, and he nearly had a heart attack at the price of it in Australia. From memory it was close to 1k to service the Unimog, making any leak in the system bloody expensive.
 

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I was talking to a radiotor specialist about the stuff in my Jaguar, and we got to talking about de-mineralised water. His understanding the de-mineralised water was the worst thing, as it is actually an acid in that state, and first thing it tries to do is get the minerals back in, mainly aluminium oxide, and that would be eating the aluminium block/head etc. Not sure if this is true.

If you don't need a proper antifreeze - the try a Tannin based coolant, old Jaguar S-type owners swear by it. I've been running it in my Discovery Tdi for 7 years now, and no problems whatsoever. Not sure if the company is still around though, could not find them on the net.

Here is an interesting article by a friend of mine on his cooling system problems.

http://www.jaguarhunter.org.au/Technical_Pages/PDF/Technical Tips Glycol & its Alternatives JDCHR HUB Jun 09.pdf
 

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Discussion Starter #15
There are radiator caps available with zink anodes - however, this will protect only the aluminium bits - and not really stop the normal corrosion issues caused by dissolved oxygen. As Ian's friend points out, you still need something to stop corrosion. Demineralised water and de-ionised water should be PH neutral - and that is the key. It is the ions (often caused by minerals/metals present in the water that causes the PH to go either way and this is what starts eating away of softer metals such as aluminium. The secret is therefore to keep the coolant PH neutral and why GM advises testing for PH on a regular basis. As the antifreeze wears out the coolant starts to go acid - time to replace - by the way, alkaline is sometimes just as bad - so neutral is key.

I think, like all systems, things need to be monitored and corrected when out of kilter. So, check that there are no electrical grounding issues, check that the PH is fine and the coolant runs clear - fix if any of these are evident.

With a neutral PH coolant and some anti-corrosion additive to stop the oxygen related corrosion things should be fine - sounds simple - but as we all know, the simple is sometimes the hardest to maintain.

The challenge is now to get the system clean ! After about 5 flushes, tea still comes out of mine - at least it no longer coffee ! I will keep at it until it stays relatively clear before putting in fresh anti-freeze and demineralised water and then I will keep a close eye on it.
 

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we have a product called water wetter it eliminates air bubbles in the coolant letting it run more effient n cooler ford has an additave for there diesels which does the same thing eliminates bubbles around cylinders that cause hot spots n corrosion guess i need bigger suitcases
 

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I run RedLine Water Wetter in my E46 M3; I have no empirical evidence to vouch for it one way or the other, but other BMW guys swear by it, so I ordered some for the 'Mog today.

The rest of my cars are air-cooled so it's a moot point :)
 

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Discussion Starter #19
MB coolant spec

OK, as usual, it often helps to consult the instructions !

WSM states that the 352 engine uses coolant spec 325.
I also found a TSN on the other side of the tracks.

Like oils, this is a seriously mal-informed subject. Make of it all what you will, but I will be sticking to MB spec.
 

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not sure if its already mentioned but you need a coolant with anti cavitation property. pretty much most that say diesel antifreeze have this.
 
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