4.5 water pump durability

[berfinroy]

I have a 1972 300 SEL 4.5 with 71,000 miles from new. Should I consider replacing the water pump even though it doesn't leak or can I reasonably expect it to remain leak free for the forseeable future? I have had some unfortunate experiences with other manufacturer's water pumps, but then Mercedes' equipment may well be expected to be better than average.

Thoughts?

[Tony H]

I would change it for piece of mind and carry the old one as an emergency spare. If your starter and alternator are original I would change them also and carry the old ones.

[97 SL320]

What sort of use does this car see? ( weekend / every day driver ? )

Are all that use this car attentive to its operation and will stop if the temps rise / odd noises ?

I tend to replace parts when they get near the end of their expected service life and before they fail in order to prevent unannounced breakdowns.

There are a two issues that come into play with the water pump : seal leakage and bearing failure.

My first pic is of a typical automotive water pump seal. There are a few other types typically found in non automotive applications and I can't be sure your pump has the type I'm referencing but the principals are all the same.

The retainer presses into the water pump housing like a cup type freeze plug. The spring loaded primary ring does not rotate and is sealed from leakage by a rubber bellows. The mating ring , seat cup and sleeve are attached to the rotating shaft or sometimes the water pump impeller.
The mating ring and primary ring are ground so smooth and flat that water can't get between them even under pressure.

Leaks can occur in two places, between the primary ring / mating ring. This is usually a small leak that could take a long time to get worse. If the rubber bellows fails, the leak is instant and major. In either case, stop leak wont fix this kind of failure.

Bearing failure can occur due to grease slowly drying out , getting past the bearing seal or due to water intrusion from a leaking seal. Signs of bearing failure can be noise or in extreme cases the fan going through the radiator.

A subjective test is to remove the belt and turn the water pump. There should be some drag during rotation ( this shows there is grease in the bearing ) and when when you start turning, there should be some amount of "stiction". Stiction is where starting friction is higher then running friction. shows that the sealing rings are being held together by the spring.

For more have a look here and do a net search for "water pump seal "

Water Pump Components | ASC Industries, Inc.

[97 SL320]

More pics / info

AGCO Automotive Repair Service - Baton Rouge, LA - Detailed Auto Topics - Preventing Water Pump Leaks and Problems

[BWhitmore]

I agree that replacing a known good water pump is premature given that water pumps give you warning before failure such as leakage or bearing failure. If you are planning to drive the car on long trips then I would follow Tony's advice; if not, wait until it gives you some warning signs.

[Graham]

Originally Posted by berfinroy

I have a 1972 300 SEL 4.5 with 71,000 miles from new. Should I consider replacing the water pump even though it doesn't leak or can I reasonably expect it to remain leak free for the forseeable future? I have had some unfortunate experiences with other manufacturer's water pumps, but then Mercedes' equipment may well be expected to be better than average.

Thoughts?

My 72 350SL has same engine. My water pump developed a small leak at about 150k miles. I wouldn't change it until you see some dripping from the weep hole on the front of the housing. Changing the pump entails quite a bit of work. You get lots of warning when they start to fail.

New pumps from MB are high quality, but expensive! Something like $400? And that may be for a reman unit. I bought a Laso pump. Was told by rep of another aftermarket supplier to not buy their pump and instead to buy the Laso because it was or was close to an OE pump. Cost me about C$150, I think.

By the way, I have my old pump still and was thinking of rebuilding it. Bearings seem OK so probably just need seal. And a way of pulling the impeller! Have tried without luck - Need a different puller. Last time I checked, MB dealer actually had a seal. But cost was high. Are there other sources for the seal?

This pdf link gives details of seal replacement on m117 water pump
https://dl.dropboxusercontent.com/u/54783344/m117%20water%20pump%2020-225.pdf