Where can you find from the engine block the water jackets of my 300m. It suspect that these waterjackets are already coroded causing water leaks. Is it advisable to put solution on the water reservoir the one used in the TV to plug leaking parts in the radiator?

The water jacket is just a name for the coolant inside the engine. It is the metal of the block surrounding the coolant.


The photo shows an engine block. The 4 bigger holes are - obviously- where the pistons fit. The smaller holes lead into the water jacket'. The coolant is held between the outer wall of the engine block and the inner wall. This area between them is known as the 'water jacket'.

The coolant circulates through the water jacket and into the radiator via the top radiator hose. As it cools it goes downwards in the radiator and then back into the engine block via the bottom radiator hose

Yes, that is a possibility. I have a 4-liter V-6 in my 1993 Ford and it had two freeze plugs that had rusted and were leaking. It was easy enough to replace them because they were on the side of the block but I learned there are two freeze plugs hidden under the transmission bell housing. It they are leaking, antifreeze would be dripping off the back of the engine.

Freeze plugs should not cause oil leaks as they are a safety device for the water jacket.

can be caused by many things.
does it leak (overheat) all the time.
does it do it at first start, parked, idling, for 5mi, or 30min.?
or only after engine warmup ,then i drive and only at stop signs
does it overheat moving fast , steady 45mph speed?
there are many tests, all are easy.
first off , it can be bad RAD,thermostat, lost coolant (ignored service) bad water pump, bad RAD CAP.(replace if bad)
or cracked engine bock, cracked head, bad head to block gasket.
to name a few.
if it only fails at stops signs look for RAD tube blockage
i use an IR pyro gun to find these.
there are 3 more tests, ask.

Sound like a head gasket is leaking. The coolant is leaking from the water jacket through the failed gasket in to the engine crankcase. The "blow back" is caused by the combustion inside the cylinder to leak into the water jacket, pressurizing it.
Drain the oil immediately and do not attempt to run the engine until you have the gasket replaced. Water in the oil will destroy the engine beyond repair.

I don't mean to sound sceptical, but how have you concluded there is not any head gasket problem? Do you mean a compression test is good? Because that will not show up any leak between the water jacket and the oil passages, via the head gasket joint. Only a pinhole leak is needed because water is, well, watery.
Has a radiator leak down test been done? This will show up water jacket leaks (there may be more than one), and give you some idea of the size.

http://www.benplace.com/pressure_test.htm

I don't know your engine well, but I cannot think of another ready way for water to get in the oil or v-v, except a cracked block, which is rare. I have read of a leaky intake manifold gasket causing it, but I can't picture that one myself.

"freeze plugs" actually are installed in a block to seal off the holes where the stuffing that is put into the casting gets removed. The stuffing is what forms the water jackets that cool the engine.
That said, there is no way a freeze plug can ever leak oil because they only cover water passages.
Keep looking and you will find the actual leak source!!

if you dont find any significant leaks .. then watch for steam out the exhaust after warm up .. or smell for antifreeze there soon after startup .. that would indicate a blown head gasket. it would have a damaged area between a water jacket passage and the combustion chamber of one cylinder ... if you can see inside the radiator you might see bubbles when running in this case .. the escaping exhaust gas (into the water jacket) can force water out of the block ... that could expain the fast heat up time .. if there is water in the block then it should take longer to heat even if other things are wrong .. a bad thermostat could cause overheating but would normall take a while before the temp reaches "peg" . same thing with a water pump if it had a damaged impeller. the only way the engine could get that hot that quickly is if there is little or no water in the water jacket .. a bad head gasket is the most likely reason for that .. of course make sure oil pressure is normal .. if the engine was not also losing water and obviously overheating then you could suspect a bad temperature sending unit ..but sounds like thats not your case .. be careful allowing the engine to get that hot .. it could warp the head causing more expense .. another frequent sign of a blown head gasket is the heater will quit working at idle but will start to work at higher RPMs... if you repair the gasket yourself, many engines require new head bolts .. you cant use the old ones over again .. the bolts are designed to stretch to accomodate expansion as things get hot .. special instructions will come with new bolts...

You should be using Antifreeze in the coolant system cause it boils at a higher temperature and
will not evaporate.plus rest protection and lubrication for the water pump. Water will rust the water jackets inside the engine and ruin the cylinder head gaskets .I suspect the leak is either a simple fix like a hose or water pump seal a big fix like a cylinder head gasket. Water can cause all of these problems.

they don't go into the water jacket, but be careful not to drill any deeper than the bottom of the bolt hole or you can go through to the water jacket, a piece of rubber vacuum hose over the drill works well to limit the drill depth.