92 190 2.3 Water Pressure Problem
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92 190 2.3 Water Pressure Problem
Could someone help PLEASE??? My 190 is blowing the top radiator hose off where the thermostat is???? It will run fine for about a day and then, off it comes????? What would be causing the pressure that keeps blowing the hose off? I have tightened it to the max and it keeps coming off....
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Joined: Jan 2006
Posts: 57
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From: Manchester, England
1993 Mercedes 190E
Okay, you seem to have two problems going on at once here:
(1) The pressure build-up is blowing off the top hose when it should be opening the pressure safety cap.
(2) The fact that an excess of pressure is building up.
Firstly, after you have made sure that the top hose is properly fixed on with nice new tightened hose clips, you should attend to the safety cap. This is the cap to the coolant reservoir which is designed to act as a safety valve and let excess pressure escape before it damages the rest of the cooling system. It might be simplest to just replace the safety cap, as they are pretty cheap, but do check that it is not gummed-up with something untoward. There should be a small 'overflow pipe' - a rubber tube which runs from the housing where the safety cap is fitted and lets any escaping stuff blow around the inner wing lower down in the engine bay.
Next, you need to investigate why there is an excess of pressure - assuming that with the safety cap attended to you still have a problem. Primary suspect for this is probably the cylinder head gasket - with a small leak allowing the combustion gasses from one cylinder to partially vent into a coolant gallery. This is often accompanied by slightly rough running when the engine is started from cold thanks to a little coolant escaping through the leak in the other direction and into the cylinder - so it doesn't fire properly when the engine is first started. A compression check will show if one cylinder is down on compression, which would pretty much confirm a head gasket leak.
How such a leak might have occurred can only be guessed at. On rare occasions some people claim that a head gasket will fail with age. more likely is that a bit too much expanding and contracting - maybe thanks to overheating at some time in the past - has lessened the clamping pressure between cylinder head and engine block. The head has to come off to deal with the gasket, under which circumstance it would make sense to give it a light reconditioning - valve grind, seal renewal, etc - and check the mating surfaces for flatness. If the mating surfaces of the head and block aren't perfectly flat then the new gasket will leak as well !
(1) The pressure build-up is blowing off the top hose when it should be opening the pressure safety cap.
(2) The fact that an excess of pressure is building up.
Firstly, after you have made sure that the top hose is properly fixed on with nice new tightened hose clips, you should attend to the safety cap. This is the cap to the coolant reservoir which is designed to act as a safety valve and let excess pressure escape before it damages the rest of the cooling system. It might be simplest to just replace the safety cap, as they are pretty cheap, but do check that it is not gummed-up with something untoward. There should be a small 'overflow pipe' - a rubber tube which runs from the housing where the safety cap is fitted and lets any escaping stuff blow around the inner wing lower down in the engine bay.
Next, you need to investigate why there is an excess of pressure - assuming that with the safety cap attended to you still have a problem. Primary suspect for this is probably the cylinder head gasket - with a small leak allowing the combustion gasses from one cylinder to partially vent into a coolant gallery. This is often accompanied by slightly rough running when the engine is started from cold thanks to a little coolant escaping through the leak in the other direction and into the cylinder - so it doesn't fire properly when the engine is first started. A compression check will show if one cylinder is down on compression, which would pretty much confirm a head gasket leak.
How such a leak might have occurred can only be guessed at. On rare occasions some people claim that a head gasket will fail with age. more likely is that a bit too much expanding and contracting - maybe thanks to overheating at some time in the past - has lessened the clamping pressure between cylinder head and engine block. The head has to come off to deal with the gasket, under which circumstance it would make sense to give it a light reconditioning - valve grind, seal renewal, etc - and check the mating surfaces for flatness. If the mating surfaces of the head and block aren't perfectly flat then the new gasket will leak as well !
