Author Topic: 6.9 water pump questions  (Read 450 times)

raueda1

  • Vintage
  • ***
  • Posts: 790
  • Assimilated. Resistance is futile.
  • Location: Salt Lake City, Utah
6.9 water pump questions
« on: 14 June 2021, 10:18 AM »
I'm planning a long trip in Aug and have mild water pump concerns.  The current pump is the old-style with round pipes.  The questions:

1.  Is the newer style with rectangular pipes bolt-on compatible?
2.  Does the pump give any warning signs before complete failure?  Obvious leaking is obvious, but anything else?  Can a pump leak intermittently?
3.  There's a little hole on top of the pump, like a vent.  What is it and does it need any kind of care?

Thanks in advance for any insights. Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

adamb

  • Vintage
  • ***
  • Posts: 630
  • 1977 450SEL6.9
  • Location: London, UK
Re: 6.9 water pump questions
« Reply #1 on: 14 June 2021, 02:57 PM »
I didn't know there were two types of water pump.  I have a spare which I've not had to use yet, fortunately.

What can happen?
- It gets damaged due to debris in the channels or rusted due to poor quality or old coolant. The blades fail to move the coolant around effectively. Can result in overheating.
- The seals leak
- The bearing wears out

I've never heard of the last one happening and I think it's the only possible cause of complete failure. Would like to hear if anybody has had to change the water pump for this reason.

AFAIK the pump is a service free item - just check belt tension as a matter of practice.

BCK1963

  • Enthusiast
  • *
  • Posts: 68
  • W116 Enthusiast
  • Location: Schaffhausen / Switzerland
Re: 6.9 water pump questions
« Reply #2 on: 14 June 2021, 09:07 PM »
The water pump of my 74 Cadillac failed due to a blown bearing. More or less entire coolant loss within short on the Autobahn.
Since heat sensors buzzed immediately there was no damage to the engine.

When driving I always keep an eye on the coolant temperature but I am not sure that I would notice such a failure on my 6.9 in time without an acoustic warning.
Bernd

1976 Merc 6.9  since 2013
1974 Caddy CdV   since 1992  (for sale)

Randys01

  • Classic
  • **
  • Posts: 261
  • W116 Enthusiast
  • Location: adelaide australia
Re: 6.9 water pump questions
« Reply #3 on: 15 June 2021, 10:07 PM »
There are 2 styles of water pump..."round" and "square".

The round pump and the square pump have their own unique base....so not interchangeable.  One design is neither newer or better than the other. Destination seemed to play a role in what pump went where. My car is late build Aus spec and  has a round pump to illustrate the point.  I did a comprehensive tech paper for the M100 club some years ago on rebuilding one.
The original bearing is a rippa.....it is not going to fly to bits in a hurry. What we usually see is a progressive weep thru the pump shaft seal which hardens and claps out after 30 years.
Disregard the hole in the top.
If you think your pump is suspect you will hear the bearing if it has gone cranky.........you will see weeping. To get some some idea of whether failure is imminent, drain the coolant...capture it..remove the drive belt/s and wiggle the pulleys/fan to see if there is excessive play.......spin it it by hand and feel for a hint of gritiness or reluctance to turn in the bearing boss.
Rarely a NOS base turns up on Ebay...most pumps are now recons which require profess rebuild because the bearings have to be modified. All NOS OE bearings seemed to have gone and NLA.
Depending on your global location  most impellors are slowly fretting away.......these are NLA ...the 600/6.3 water pump is sufficiently diferent as to offer no hope!

raueda1

  • Vintage
  • ***
  • Posts: 790
  • Assimilated. Resistance is futile.
  • Location: Salt Lake City, Utah
Re: 6.9 water pump questions
« Reply #4 on: 16 June 2021, 10:00 AM »
There are 2 styles of water pump..."round" and "square".

The round pump and the square pump have their own unique base....so not interchangeable.  One design is neither newer or better than the other. Destination seemed to play a role in what pump went where. My car is late build Aus spec and  has a round pump to illustrate the point.  I did a comprehensive tech paper for the M100 club some years ago on rebuilding one.
The original bearing is a rippa.....it is not going to fly to bits in a hurry. What we usually see is a progressive weep thru the pump shaft seal which hardens and claps out after 30 years.
Disregard the hole in the top.
If you think your pump is suspect you will hear the bearing if it has gone cranky.........you will see weeping. To get some some idea of whether failure is imminent, drain the coolant...capture it..remove the drive belt/s and wiggle the pulleys/fan to see if there is excessive play.......spin it it by hand and feel for a hint of gritiness or reluctance to turn in the bearing boss.
Rarely a NOS base turns up on Ebay...most pumps are now recons which require profess rebuild because the bearings have to be modified. All NOS OE bearings seemed to have gone and NLA.
Depending on your global location  most impellors are slowly fretting away.......these are NLA ...the 600/6.3 water pump is sufficiently diferent as to offer no hope!
Wow, who knew?  Great info, very helpful.  As noted above, my engine (euro) also has the round version which I reinstalled during recent rebuild.  It didn't seem to have any of the issues you mention.  But I've got a square version from a USA parts car that I was keeping in reserve. 

So, if I understand right the respective pump bases or housings are NOT interchangable.  IOW, I can't just bolt the square one onto my car.  But is the pump impeller/core assembly interchangable between the respective bases?  If not then the square one is no use to me and I'd put it up on eBay.  If so then I'd try to get the core out of the square base to hold in reserve.  Thanks again and cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01

  • Classic
  • **
  • Posts: 261
  • W116 Enthusiast
  • Location: adelaide australia
Re: 6.9 water pump questions
« Reply #5 on: 17 June 2021, 12:44 AM »
round pump round base.  Square pump  square base. How this came about I've never understood.  Two different pump manufactueres..one got a creased copy of the plan?! ;D

3l33ter

  • Classic
  • **
  • Posts: 108
  • W116 Enthusiast
  • Location: San Francisco bay area
Re: 6.9 water pump questions
« Reply #6 on: 17 June 2021, 01:30 AM »
I'd say just drive and enjoy, and keeping an eye on the temperature gauge is a good habit to always have.
'75 280S
'77 6.9
'82 300TD