All, need help with this. My trusty diesel has developed a really bad coolant leak. I feared a head gasket, but now I don't think so. I have narrowed it down to an area between the alternator mounting bracket and the block, just above the oil pan. I'm wondering if there is a freeze plug in that area of the block which is covered up by the alternator mounting bracket. I'm not in a position to pull the alternator and the bracket off now.

For reference, this appears to be a region just aft of where the dipstick disappears into the block.

Does anyone have a photo of a bare block on the passenger (right) side or a drawing of the 606 block to show if there is a freeze plug there?

The car is pretty much not drivable now as the leak rate is quite fast - drip drip drip almost as fast as you can say it.

Rgds,
Chris W.
'95 E300D, 412K on hold

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Objects in closer are mirror than they appear.

Google "om606 block" and select "images". I just looked, and there are a few pictures that may help.

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Current rolling stock:
2001 E55 183,000+ Newest member of the fleet.
2002 E320 83,000 - The "cream-puff"!
1992 500E 217,000+
1995 E300D 412,000+
1998 E300D 155,000+
2001 E320 227,000+
2001 E320 Wagon, 177,000+

Prior MBZ’s:
1952 220 Cab A
1966 300SE
1971 280SE
1973 350SLC (euro)
1980 450SLC
1980 450SLC (#2)
1978 450SLC 5.0
1984 300D ~243,000 & fondly remembered
1993 500E - sorely missed.
1975 VW Scirocco w/ slightly de-tuned Super-Vee engine - Sold after 30+ years.

If the 606 is anything like the 603, the water pump is above the alternator. There's a housing that attaches to the block which accepts the thermostat and water pump. My first guess is you need a new o-ring for the pipe through which coolant from the monovalve attaches to the rear of that housing.

Are you part of Jeremy's thread - 1995 E300D Monovalve Problem ?

Sixto
87 300D

My water pump went out and leaked small amount of coolant out the tube coming from the front bearing. The tube dumps out by the alternator bracket. From the sounds of it you need a pump front bearings are leaking.

Appreciate the suggestions! Believe it or not the water pump is original, so it could be the reason. I'm biting the bullet and having the car flat bedded to my indy on Monday.

I have the original monovalve and Jeremy and I have messaged about it. I think the diaphragm in mine is out to lunch, but I get enough heat to get by. And mine is not cracked. I'd buy a new one, except for what Jeremy has found out about the issues on new ones.

Rgds,
Chris W.
'95 E300D, 412K and holding

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Objects in closer are mirror than they appear.

Answer? Water pump. So - what is the lifetime of the naturally aspirated 606 water pump? Let's round it off to 400K.

Rgds,
Chris W.
'95 E300D 412K

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Objects in closer are mirror than they appear.

Good to know, ive got a 300d 2.5 turbo in family service with the original water pump at 300k - so I'm good for another 100k.

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98 Dodge-Cummins pickup (123k)
13 GLK250 (135k)
06 E320CDI (323K)
16 C300 (62K)
82 300GD Gelaendewagen (54K)

Good to know. I've been changing them too soon.

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Jim

I guess if Mercedes Approved coolant is used, it provides the right environment for these water pumps to last (low corrosive action and adequate lubrication).

RE: Monovalve, I replaced mine with an earlier, much less expensive one, and more reliable one from the earlier 1990's diesel 124s. I capped off the loop coming from the driver's side and going in back of the block. I already had an extra coolant loop installed when I added a WVO tank in my trunk.

Jeremy thinks the additional loop added in the coolant circuit for the 1995 e300 may have been done for emissions reasons.....keeping the engine at a more constant temperature.

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-- Chris

'95 E300, 216k miles, Silver Surfer
'05 E320 CDI, 138k miles
'07 S550 4matic, 69k miles

Gone but not forgotten:

'76 300D, 350k miles?, SOLD in 1995
'75 240D, 300k miles, SOLD in 1991