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?
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.
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???
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
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
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.
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.
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?
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
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
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
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