what causes the water pump to fail?
 

id like to know exactly what it is that causes the waterpump failures that seem to be the bane of these cars.

i have a 1990 300E 2.6 which is leaking water from the region just behind the water pump and adjacent to the block. it gulps about half a gallon every other day and the temperature sometimes stays in the 100s even when on the freeway. oddly enough, if i turn on the heater it still blows hot, but previously when my windshield washer heating coil thingamjig was broken and my coolant was leaking into the washer bottle, this didnt happen. no heat, i guessed coz there wasnt enough water to pump to the heating system.
anyway, i dont know if the water pump problem is a failure of the actual part or a gasket or corrosion of materials or what.
is it the gasket deteriorating over time?
materials?
part of questionable build?
or just age?

and is there anything else that i should look at before condemning the water pump.
cheers

i think the most common mode of failure is seal failure. the pump is pretty simple. it has a housiing, bearings, an impeller and a shaft that goes to the drive pulley. the seals separate the water from the air on one side and the water from the oil in the bearings on the other side. as the shaft turns it wears the rubber on the seal til it wont seal any more.

they can also fail by the impellors wearing or corroding away, and the bearings sometimes fail, too.

but the seals i think are the most common. when they fail the water gets past them and comes out the weep hole in the housing.

tom w

Also, too much tension on the belt will overload the bearings.

Get a good quality water pump.

I have learned that one of the most important services on any water cooled engine is to drain and refill the coolant system with a quality anti freeze. With age, the lubrication qualities of the anti freeze are depleted, however, the properties that keep the cooling system from freezing haven't diminished much. Most people take that attitude that if it is still protecting the engine from freezing and the "color" looks good, then it is still good. I believe that changing anti freeze every two years is preventative maintenance for the engine and cooling system. I can honestly say that I can never remember replacing a water pump in any of my MB's and I usually drove them to 175 - 200K miles before retiring them. I learned early in my driving life that you can either pay for maintenance or you can pay for repairs. Usually, the repair costs far out weigh the cost of preventative maintenance. Dusty......

Good point Dusty. I'll change the coolant in my 300SE soon.

I don't know what makes MB's coolant better than anyone else's, but for some reason, everyone that I have ever heard discuss this, has said that you should only use the MB coolant in MB cars. The claims are that it is best for the aluminum engine block parts and prevents cavitation in diesel engines. Since disposal has been a problem for me for many years, I always left this service to the MB dealership. I did notice a few weeks ago, that there is a name brand coolant that is the same, Valvoline Zerex GO5. What I also found interesting is that my local Carquest dealer also carried the Mercedes branded coolant on his shelf. When I asked about this, he said that they can order it from the Carquest warehouse. When mixing coolant, you should use only distilled water. The reasoning for this is that distilled water has no mineral content and that the PH is 7.0 +-.

Here is a link to some information about the MB anti freeze.

https://www.peachparts.com/shopforum/Valvoline Zerex G05 Antifreeze/Coolant Phosphate Free, Long Life Hybrid Technical Bulletin (pdf).......

last question..... Do you know how to make anti freeze???? :D

You cannot make antifreeze at home unless you have the corrosion inhibitors needed to prevent electrolytic corrosion between the aluminum and iron engine parts. The aluminum will corrode away (it becomes a soluble salt) and electric current is generated when aluminum and iron are connected by a conductive liquid.

MB coolant is the best to prevent this -- GM's DexCool type coolants have a tendency to precipitate silica particles, and that grinds up water pump impellers and seals pretty fast. Phosphate based corrosion inhibitors used in "cheapo" older style green coolants precipitate in the radiator, plugging it and the deposits usually cannot be removed, along with allowing severe corrosion very quickly.

Use the MB coolant, it's far cheaper than blowing a head gasket because the head corroded out around the combustion chambers (my sister's Volvo did just that -- huge holes).

Peter

what about the cast iron 4.5's?
 

What about the early all cast iron engines and heads. Would MB or the G05 be required for these engines?

This part of my reply was meant as a joke........ the answer is.......






hide her flannel pajama's.......:D

your leak is going to be the large o ring at the rear where pump seals to engine these bolts hard to get to sometimes not tightened all the way.but also maybe engine wasn't cleaned properly last time pump replaced.

thank you all for your help and information.

am i to take it that the fault could just be the seal and the waterpump could be fine? labours gonna be the same for that seal and a water pump so i may as well get a pump. is that logical?

If you already had the pump uninstalled, it would be crazy not to replace it with a new one, unless funds are really really tight. Do you want to do the job twice?

thats exactly my thinking.

can i get an idea of cost while im at it. its got to be done sometime soon and i dont know if im going to need to raid the retirement fund.
fortunately im in a situation where i know im unable to get it done for at least a month. too many pressing issues. this will allow me to put some money aside.