Coolant loss M103?

I have a 1989 Brabus 3.6, M103 engine. I am experiencing coolant without an obvious cause. The same thing was happening to me 6 months ago but oil was
in the coolant so I changed the head gasket (which is £564.87!) and it's been fine until recently. I thought it may have been the water pump bearings, only leaking when turning and evaporating to quickly on the hot engine to leave a trace so I've changed that along with upgrading the thermostat housing and renewing the pipes. It takes about 1l of coolant every 250 miles or so depending on how I drive. If I thrash it it seems to use it at a faster rate. My water is NOT contaminated at the moment so I pray it's not the head gasket again. I ran the engine for about 5 minutes today with the expansion tank cap off, some of the time at a steady 3500 rpm. The level in the expansion tank remained steady and I didn't see a coolant start to pour out of the expansion tank as I would expect if it was the head gasket. I felt the pipes around the heater valve and they're dry, without any sign of coolant leakage. However the pipe on the other side which leads hot coolant into the heater matrix did have a touch of what seemed to be coolant on it, unless it was water which fell on to it from the windscreen washers? I was thinking may be the heater core or perhaps the radiator are at fault? Any advice would be much appreciated. Thanks
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Update: today I re-bled the cooling system by starting the car and letting it warm up with temperature set to MAX and fan speed 4. After it took as much water as it could I started revving it. I noticed that as I rev it it takes water from the expansion take which fills back up as the engine slows down, I'm guessing this is normal operation? Smoke was clear even when revving the engine while bubbles where not developing in the expansion tank. Additionally the hot air in the car didn't smell of coolant so I'm thinking that the radiator seeping coolant under very high pressure is the only solution? I have already replaced the expansion tank cap with a shiny new Mercedes original.

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Sounds like a cracked head, one of my customers was experiencing the same problem, constantly had to add water and no appearent leak. Check the overflow tank inside the passenger fender (2 overflow tanks). The tank could be cracked and you may lose coolant that way. But, I got a feeling.....cracked head. Martin Autobahn Auto
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Hi Martin,
Thanks for taking the time to reply. However wouldn't a cracked head give the same symptoms as a head gasket though. I mean the water has to somewhere. So it would either leak externally which would be visible, or internally which would either mean coolant in the oil or coolant in the combustion chamber (e.g. steam in exhaust) neither which I am seeing. I will check the overflow tank in the passenger fender, but how would this lead to a leak?

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The situation I was refereing too was very strange, at first he would be low on coolant every other day while he was driving 30 miles day, then I noticed that the car was running rough for 5 minutes whenever it was not used for two or three days. Well the running rough was water build up in # 6 cylinder. Once the water burned away the car was running smooth. The customer then drove the car all the way from Virginia to Mexico and back, but then the winter hit and the problem became worse. (there was no visible smoke from the exhaust). Martin Autobahn Auto
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Thanks for the reply Martin. I am actually experiencing rough running some of the time it is intermittent and gets better than worse randomly. But it's definitely never running as smoothly as I know it can. Still a mystery where that water is going though?! Is there any way to test for a cracked head without removing it and pressure testing it? Thanks

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Being burned in little amounts whenever you feel the engine running rough. You could try to have it pressure tested to see if water gets into a cylinder, but it could be a slow overnight process and you may not know until you pull the head. Once you pull the head you can see the difference in the cylinder that was taking on water, it is usually much cleaner looking in the combustion champer. Martin. Autobahn Auto
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Hi Martin,
I just thought I'd let you know that you were right. I had it pressure and combustion tested. Even at 2 bar, no leaks. However when he placed the blue solution over the expansion tank and started the car it turned yellow. I can't believe it! I think the head must have been skimmed bellow its limits because I remember being told that was badly warped when I got it skimmed. Thanks for your insight.
Regards,
Mehmet

it's
where
cylinder,
pull
chamber.
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Hi Martin,
I just thought I'd let you know that you were right. I had it pressure and combustion tested. Even at 2 bar, no leaks. However when he placed the blue solution over the expansion tank and started the car it turned yellow. I can't believe it! I think the head must have been skimmed bellow its limits because I remember being told that was badly warped when I got it skimmed. Thanks for your insight.
Regards,
Mehmet

it's
where
cylinder,
pull
chamber.
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