I have a 1992 500SL that has developed a very slight coolant leak. I have written to the forum before asking advice on the problem. It is a small leak from the connection on the upper drivers side of the radiator that has left a trail of dried white residue running down the radiator. I have decided to replace the hose and clamps. I am not a mechanic, but this seems to be a simple enough repair to try myself. It would seem pretty straightforward. Loosen the metal clamps on both ends of the rubber hose, remove the old hose, Replace with the new hose and tighten the clamps. Am I missing something? Or, problems to watch for? Thanks. JRoe

Drain the coolant down enough so that it is below the lowest point of the hose to be replaced. This is best done with a cold engine. The most important think to remember is to not overtighten the clamps. Also clean the areas that the hoses slide over. A clean sealing surface seals much better than a dirty one does. Inspect the upper radiator neck for cracks. Yours should have a metal sleve on the inside. If it is cracked replace the radiator. Cheap compared to a new engine.
Good Luck and have fun.

I always recommend to replace the clamps!! They are cheap and do fail.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
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Is draining from the lower hose enough to get most of the coolant out of the engine without using the engine plug ?
All I want to do is a drain and re-fill.
Thanks.

There should be a drain plug on the radiator. If you are looking at the front of the car, look at the lower left side of the radiator (passenger side.) Check the front of the radiator (bumper side.) That's where mine is.

This way you shouldn't have to mess with draining the block.

However, as long as you're draining some of the coolant, it's not that much work to drain the entire block and replace the old coolant with new. Cheap insurance.

Let me make sure I understand.
Is it possible to drain most of the coolant by just draining from the lower drain plug in the radiator ?
If the only way for a complete drain is by also unplugging the block, I will do that as well.
I'm always confused about the role of the thermostat. Is the coolant entering the radiator from lower hose and exiting the top or vise versa ?

Draining only the radiator only will drain out different amounts of coolant depending upon the engine and the location of the thermostat. The normal coolant change interval is 3 years. Now if you drained the radiator once a year and refilled it with a 50-50 mixture of a top brand antifreeze that is approved for use with aluminum, then you probably would be OK. Remember that MB says all of it every three years.... Your choice, a little maintanence is better than none at all.

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Your question below with answers:

Is it possible to drain most of the coolant by just draining from the lower drain plug in the radiator ?

I would guess that probably 50% or more of the total amount of coolant can be drained through the radiator plug. This will drain the entire radiator, tank, and as much of the block as is above the lower part of the water pump. Make sure you open the pressure cap before you start to drain.

If the only way for a complete drain is by also unplugging the block, I will do that as well.

Yes, the only way to drain the entire coolant contents is to drain the block. Even then, some coolant will still be in the heater hoses and core, but that is a relatively small amount.

I'm always confused about the role of the thermostat. Is the coolant entering the radiator from lower hose and exiting the top or vise versa ?

Vice versa. The coolant travels from the radiator to the water pump through the lower hose, and is then circulated through the engine block. Until the coolant reaches operating temperature (usually around 180°F), the thermostat remains closed and there is no circulation to the radiator through the upper hose. When the engine reaches operating temperature the thermostat begins to open allowing coolant to travel to the radiator via the upper hose. The thermostat modulates (varies its amount of opening) to try to maintain a relatively constant temperature of coolant in the engine.

Thanks, metricman and TimBru99 -

After a "complete" drain, I think it is safe to assume enough coolant is introduced into the system by filling through the expansion tank or radiator cap.
The level should drop in the expansion tank once the thermostat opens up and more coolant introduced to top off.

Safe procedure ?