So my wife tells me nonchalantly that the temp hit 120 y-day in the 85 300SD and she turned off the air, fan and the radio and it came back to around 97 degrees. She tells me this as I see 108 degrees on the temp dial as I am driving the car. After raining for 25 days out of the last 40, it's been 97 in CT the last two days. So when I get home, I pop the hood and see the coolant tank bubbling and then recede and water dripping at the left side of the radiator. I proceeded to add 1 3/4 gallons of water and drive around the block, pop the hood, look underneath and - no water leaks?! What's going on? Is my water pump or radiator at fault here. Is it just so hot that the water is overflowing? Strange...

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85 300CD Signal Red/Tan sold
83 300D Manganese Brown 109K
97 E420 Midnight Blue 197K sold
98 BMW 328i Vert White 100K, sold
95 BMW 525i White 125K, sold
93 BMW 525iT Red 193K, sold
95 E320 Green Wagon 125K, sold
94 E320 White 127K, sold
85 300SD 156K Grey (Annie), sold
84 300D Lapis Blue 170K (Judy), sold
99 ML 320 Black (lease), 1998 C230 White (lease)
00 Honda S2000 Red (lease)
86 Mercedes 300E (sold)
84 Porsche 911 Red (sold), 1965 Porsche 911 White (sold)

I probably need a new water pump. Any experience or advice for the removal and change?

edge,

Coolant dribbling from the radiator may not be coming from the water pump. There is a drain on the bottom of the radiator that may be leaking, and there is a large hose connection at the top on one side and the bottom on the other side. These hose connections can leak too. If the water pump is leaking it will leak out a small weep hole on the bottom side of the water pump casting.

With that much air in the system you probably were not running the pump fully submerged the entire time. This is not good for the seal, so replacing the pump may be in order even if it was not the original problem.

As for removal and replacement, this is a relatively frequent task covered on the site. The process involves taking the fan and fan belt off, then removing the pump, cleaning the sealing surfaces up and replacing the unit with a new one and new seals. IF you have some corrosion (the pump is steel and the housing is aluminum, so, it is not a shock to find some pitting and corrosion under the rubber gasket). I put the unit back together and lubricate the bolt holes and new fasteners (old ones if I do this away from a source of new fasteners, but I wire brush and lubricate them first) with high temp synthetic assembly grease.

The fasteners are steel and the housing, with tapped bolt holes is aluminum as noted earlier. I would recommend soaking them in a good thread penetrant first. If you break a fastener off you have to take the housing off and remove the broken bolt. Not the end of the world, but it adds some time and a trip to buy another gasket if you are not prepared. This is also why I lube the pump fasteners and the cleaned out tapped holes with high temp synthetic assembly grease - it is still there when you have to take things apart again, and they are not corroded together.

There are also other issues with the access, some take the radiator out and others do not. I have not worked on one of these so I do not know if the radiator removal is required.

Good luck, and I hope some of this proves helpful. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Thanks Jim, I'll take a closer look tomorrow when I have more time. it just seemed so strange that when I filled the overflow tank, I couldn't find a leak.

So I drive it around a few miles, check the hoses, they are on tight., the upper weep hole is dry on the water pump (it's too damn hot here to look for the weep hole on the bottom of the pump). Damn, everything's dry, But I had to add so much water the other day. Now I had changed and flushed the coolant a month ago. I'm a bit stumped, there's no water leak to be found.

Replace the radiator cap, it's not holding pressure and allowing the coolant to boil. It will blow out the overflow on the pressure tank.

You may only have a leak when fully pressurized, too -- my Volvo did this over the winter, had a bad heater hose on the back of the head, only leaks when there is pressure in the system, only drips enough to smell coolant otherwise. Had to use a pressure tester to find it.

You can either borrow or buy a pressure tester -- it fits on in place of the cap and is a pump with a pressure gauge. You pump it up and watch to see if the pressure goes down. If it does, you have a leak, and can usually find it under pressure.

The water pump can leak out the bottom weep hole and the coolant spins off the fan, so you don't see it much.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

So I get a pressure tester from Autozone on their free loaner program and pump it up to 17 psi...no leaks! I do it again to as much as I can pump it up to.. 17 psi again. Again no leaks, no loss of pressure. Drove it doing chores and saw that the temp reached 105 degrees, got home and saw that I was losing coolant through the overflow hose as you suggested, Peter. Is the fix simply replacing the faulty pressure tank cap? Thanks, all.

edge:

Yup. Get an OEM one, the aftermarkets sometimes aren't high enough pressure.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I thought about it some more...check my fuses and found that the fuse for the aux fan was out! Apparrently, this caused the overheating in stop and go traffic with a loose overflow cap and for coolant to be lost through the overflow valve. Thanks, guys for all your help.

__________________
85 300CD Signal Red/Tan sold
83 300D Manganese Brown 109K
97 E420 Midnight Blue 197K sold
98 BMW 328i Vert White 100K, sold
95 BMW 525i White 125K, sold
93 BMW 525iT Red 193K, sold
95 E320 Green Wagon 125K, sold
94 E320 White 127K, sold
85 300SD 156K Grey (Annie), sold
84 300D Lapis Blue 170K (Judy), sold
99 ML 320 Black (lease), 1998 C230 White (lease)
00 Honda S2000 Red (lease)
86 Mercedes 300E (sold)
84 Porsche 911 Red (sold), 1965 Porsche 911 White (sold)

Hey Peter. Hats off to you man. Thats a pin point diagnosis. Folks like you keeps me browsing this forum regularly.
Thanks

MVK

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One penny saved is three penny earned.

1985 300D Turbo 179,000miles

The 300TE did exactly the same thing two years ago after I recharged the AC. Was fine as long as you were moving, but lost coolant when you stopped after a highway run. No pressure in the coolant tank, bought a radiator cap, fixed. Still needs a new visco clutch (sitting on the floor next to the filing cabinet at the moment, won't get put on for the trip this weekend!), but no more coolant loss.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I have about the same problem but with a 1995 E300D. I just bought the car about 3 weeks ago. It has been running fine. I came home tonight and my wife said that the coolant light had come on today. The temp. outside was a high of 48F. I looked at the over flow tank and it was empty. The upper radiator hose was empty. The lower hose was not full. She said she drove the car about 5 miles with the light on, went to the grocery store and then drove home. The thermostat was below 80. Not enough coolant to let it register a temp. I am not familiar with this engine. OM606 I assume it has an aluminum head. How much damage could have been done to the engine? Where do I start? I will have to rent a coolant pressure pump first. What else?

Any help with this engine would be appreciated.

Thanks,

Mike

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1983 300DT 173,000miles sold
1983 300TDT 320,000miles sold
1985 735i 189,000miles sold
1986 528e 210,000 miles sold
1991 740 Volvo 250,000 miles
2002 VW Jetta TDI 32,000 miles sold
1995 E300D 137,000 miles
2004 Dodge Sprinter 26,000 miles
1986 325e BMW 94,000 miles
1986 325e BMW 148,700 miles
Mike