Coolant dumping out of water pump
 

1987 300SDL
I’m having an issue with my coolant system dumping coolant on the ground out of the water pump. I’ve had to replace ½ gallon of coolant in the last 2 weeks. It’s getting close to the 100 degrees in the central Texas area, but I didn’t have this issue last year.

*replaced coolant tank cap
*replaced water pump 8 months ago
*replaced thermostat
*replaced radiator ( Behr)
*replaced top and bottom radiator hoses

I’ve flushed the system twice when I replaced the items.
Running the MB coolant with distilled water. I believe the water is coming from the water pump area, because the water is always in the front of the car. I’ve gone under the car and haven’t found a leak on any of the new hoses or plug in radiator hose heater. I’m not sure what would cause the water pump to open up and dump coolant (pressure / temp). I’ve noticed that my temp is just a hair over 80C (normal).

Thank you

That's what happens when the water pump shaft seal fails.

A small mirror held under the center of the water pump should reveal the leak.

X2. It's never happened with my MB (original water pump still), but that's been the normal failure mode on lots of other cars I've had. Sometimes it only leaks when the system is pressurized but as it gets worse, you could loose coolant fast enough to get stranded. It's not a repair to put off!

Bad pump shaft seal. I once replaced my "87 pump and the new one lasted less than a year.

I put it off for a while on my SEC, and it rapidly went from loosing a little bit, to loosing a lot fast.

A friend's m103 motor had it's pump fail even more spectacularly, in that it wasn't just seeping or dribbling, but full on gushing out, limited by the size of the 3/8" hole in the pump nose.

8 months on a pump isnt very good.
Is the coolant that you are replacing the correct type & blend?
Has the coolant changed color?
How come you have replaced so much of the cooling system?
Have you been using poor quality water to mix with the coolant?
Do you have a head gasket leak?

Definitely a shaft seal failure if it pouring out the pump. Would be interesting to know why it has failed.

Just a few things to consider. Hope it helps!!

Good Luck!!

What IS the "correct" type/blend of coolant? The $25/gal. MB stuff?

Thanks everyone for your help, I can't believe its the pump. I just replaced that this year.

I've been using distilled water and MB coolant from the stealership. 50/50 blend because I live in Texas.

I've replaced so many parts of the coolant system, because I had the money at the time, and I was afraid of the MB alum HEAD on my 87 300SDL. I read if you allow it to over heat it's over.

I can't say the coolant has changed colors its still the red/ pink color.

And I don't believe that I have a head gasket leak.

Thanks for your help, I'll be contacting the place I got my coolant pump from.

Do the 300 SDL's require the G05 coolant like my 300SD? If so, it is a clear goldish color.

Exact substitute (Chemically) for MB Coolant
 

(It's what the MB Coolant really is)

Zerex G05

Where did you get the replacement water pump?

The water pumps from the MB dealer and the WorldPac dealers are generally pretty good. Not sure what you'd get from Autozone, etc.

Ken300D

MB coolant is gold, same as Zerex G-05, and available for $15 (even from peachparts...), not sure why everyone always claims its really expensive. My WP failed last year and it gushed...pretty much equivalent to pouring a bottle of water constantly. Amazing I even made it home in fact (had about 30 gallons of water in back just in case). A reseal fixed the issue and wasn't too hard...been holding since. 8 months seems pretty short, I'd pressure test the expansion tank cap if possible to make sure there isn't extra pressure on the system.

Zerex G05 is cheaper then the coolant I get at the stealership, but I couldn't find it locally anywhere in Austin TX. So I just picked some up at the stealership.

The water pump was ordered from phil,

Purchased Items:
Qty Description Brand Sku Price Total
Vehicle:Not specified
1 Water Pump
packing Size:piece; Years:; Per Car Qty:0; BRAND: GRAF MBZ078804 $102.77 $102.7

Has anyone else had this issue with the GRAF pump before?

Believe it. It happens. You need to confirm it is the pump - as has been suggested, there is probably a weep hole on the bottom that drains coolant when the seal fails. It's just a manufacturing thing, some times you get one that last a lifetime and sometimes it lasts a couple of months. I had one fail after a few months before, but it had a lifetime warranty so they replaced it for free.