Losing water - head gasket?

I've got a W124 Brabus 3.6 saloon/sedan based on a 300E M103 engine (SOHC). When I go on long journeys, for instance today I travelled 100 miles to Leicester (cruising around 70-100mph most of the way), the car loses around
2 litres of water. It only starts overheating when in traffic. I have checked all water connections except for the ones where the heat exchanger is but as this is a recent problem I don't see how that could be a factor. I filled the car with water and just made a 15 miles journey and there was no water loss. The thing that makes me think it is the head gasket is that I can petrol in the expansion tank. However there is no oil-water mixing as I would expect to see with a blown head gasket. When the car is water deficient the oil pressure gauge is unstable floating around 1 bar erratically. Any ideas?
Thanks
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Could be cracked head too, look for white smoke (steam) at exhaust. Sell quickly.
-Kent
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a tad unethical doncha think, kent? how would *you* like to buy a car with an undisclosed fault like that?
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Check the engine's water pump before doing anything with the headgasket. Water pumps have a shaft seal that wears out over time; this would explain the coolant loss on a long drive. Erratic oil pressure is probably because the engine is too hot.
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Hello My 400 SEL motor's oil pressure in hot conditions is about 1,5 kg. Motor temperature is 90 Degrees Celcius. Is this normal?
Ripa

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yes. assuming it's not a brand new engine.

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Thanks for the replies everyone. I actually have a new(ish) water pump on the car as this went about 5 months ago so I changed it. Only in the last 2 months have I noticed this problem. Also, about the cracked head theory, if the head was cracked wouldn't I notice a lack of power? Acceleration and top-end seem to be not to have changed at all. Could the radiator be leaking water when the water system is under high pressure i.e. +4000rpm, I have never seen any water dripping under the car or on any components in the car itself. The radiator wouldn't explain the petrol in the water though :(, unless it's AT oil which is mixing with the antifreeze and giving a smell similar to petrol???
Thanks

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If you have never seen a puddle under the car, especially when the engine is first shut down on a hot day - that's when the engine is at its hottest and a leak will show itself - then you are right to be suspicious. But don't overlook the very simple items - like a leaking pressure cap.
A shop with a hydrocarbon tester (for emissions checking) can "sniff" the coolant and tell you whether the smell in the coolant is gasoline or oil.
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You will not detect and performance difference with or without a cracked cylinderhead. Overheating and coolant loss are the usual symptoms, also white smoke in the exhaust soon after cold starts as any coolant that's leaked into the exhaust burns out.
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And don't assume that your "newish" water pump is a good one, I had a (non- M-B) rebuilt water pump last only 15K miles before it leaked.
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i agree with T Lambach: the symptoms you describe are those of a failing water pump.

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I've noticed a similar leak in my own car ('79 300SD), that's not apparent on short drives, but whenever I drive 90 miles or so, there is some coolant loss. In my case the fix was pretty easy (but not obvious at first). The control valve to the climate control heat exchanger was cracked and leaked slowly. That could be another cause. Don't know about that smell though.
Daniel

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Just to say today I smelt oil in expansion tank so I guess a head gasket is definitely in order if not more. Strange thing is I got 151mph out of it on today so it must be a small leak. Probably (hopefully) not a cracked head (although I did see white smoke/steam out of the exhaust :( ) in order to get that speed out of the car. Can cracked heads be repaired or would I need a new one, if it's even possible to get a new one!? I'm obviously going to try to sort this out ASAP but am I doing any long term damage to the engine by continuing to drive it?
Thanks

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I had exact the same problem with my 91' MB300E-24v (w124). I changed the raidiator and it solved the problem.

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I have recently begun to smell engine oil in the expansion tank too. I can't work out how petrol or engine oil can enter through the radiator. On my car only the water and transmission oil pass through the radiator. The (engine) oil cooler is totally separate. Could it really be the radiator?! I thought it was weird that I could still get 150mph out of the car. Your response is much appreciated and any further light you can shine on the matter would be too!
Thanks,
Mehmet

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sounds like an internal leak. The propular product sold in MB's parts department may be the inline 6 cylinder head gasket.
The leak may not affect your car's performance unitl the cooling system dry out.
Take your car to a workshop, don't waste time and money topping up the tank with coolant. The job for changing the gasket is around NZ$800 here
Keith E14 4NS

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