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Old 01-05-2016, 12:13 PM
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Join Date: Nov 2011
Location: New York
Posts: 159
Coolant leak at ?water pump?

I have a coolant leak on a 300td. Not sure if it's related but last night was the first real cold night we have had this year (5 degrees maybe?). This morning I was working on other problems and after the sun had been on the car for a little while I started to notice a little leak. It's coming from what I assume is a water pump hose? Is the water pump located at 11 o clock when looking down at the fan from the front bumper? If so then I can see coolant pooling at
The top of the hose that comes out the bottom of the pump.Want to research more but need some search terms...

:;edit:: now that I think of it my cabin heat was pretty Luke warm yesterday so maybe the leak is not related to something freezing and breaking...but nonetheless I wanted to find out the name of that hose so I could research and buy a new one if needed::

Last edited by adamkat22; 01-05-2016 at 12:24 PM.
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Old 01-05-2016, 12:30 PM
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Join Date: Sep 2007
Location: Long Beach,CA
Posts: 26,499
To find leaks you may need to get a Flashlight with a strong beam and a Mechanics/Dentist type Mirror so you can see it.

It has been unusually cold out here in S CA and I have found 2 cases on My House where the Faucets that did not leak during the day were found dripping a bit in the Morning. Tighten the valve more stopped it.
I think that was because the rubber washers shrunk a little in the cold. Old inelastic Hoses could also shrink.

There is 3 Hoses. The Upper Radiator Hose, the Lower Radiator Hose and the Bypass Hose wich is only about 2.5 inches long.

When I first got the Car in 2007 the Bypass Hose area was seeping. I decided to change all 3 of the Hoses.

For the Bypass Hose I also removed the Upper Housing it was attached to. I did not have issues with breaking Bolts that is common when removing any of the Coolant System Bolted on Parts.

However, what I found is that I had deep corrosion/pitting under the Hose with the pitted areas being full of that powdered corroded Aluminum. Being sort of a powder it of course leaked in the case of the Bypass Hose.

I wire brushed out all of the white corroded area and or scraped it down to the bare Aluminum, degreased with Brake Cleaner and filled in the low spots with the long curing JB Weld as it can take the temp.

In order to contour it I taped over it.

After it cured and the tape was off I had to fill in some recesses with more JB Weld. When that cured I filed and sanded it down so the Hoses would seal.

Where the Upper Radiator Hose made contact with the Thermostat Housing was also pitted but not as badly.
84 300D, 82 Volvo 244Gl Diesel
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Old 01-05-2016, 02:43 PM
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Join Date: Sep 2006
Location: Middle TN
Posts: 3,549
A pressure tester will help diagnose coolant leaks. I found the bypass hose available for little money but many places wanted way more than seemed reasonable. I don't remember the source.

Also, research if you determine that the water pump is at fault. Bolts can be a challenge to remove without stripping or breaking.
85SD 240K & stopped counting. 84SD 180,000. Thinking of painting both.
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Old 01-06-2016, 03:16 PM
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Join Date: Aug 2010
Location: Sacramento, CA
Posts: 2,474
The fan clutch bolts to the water pump. The water pump is round and thus on the centerline of the fan. It has a small "weep hole" (usually at the bottom) that is intended to let you see when the internal seal is leaking. You usually see white limey deposits if a leak, depending on what coolant you use.

More likely, you are looking at the "thermostat housing", to which the large "lower radiator hose" attaches. Coolant hoses should be replaced whenever they show surface cracks or other aging. If yours is a 1980's car (always tell us, please), then you probably shouldn't still be using the original coolant hoses. To replace the large, short "bypass hose" on the bottom is bad, it is easiest to remove the T-stat housing, and you will need a new gasket. I bought 16 mmID silicone hose for that since I want it to last.
1984 & 1985 CA 300D's
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Old 01-09-2016, 07:52 PM
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Join Date: Nov 2011
Location: New York
Posts: 159
it was the bypass hose that i was talking about. i brought the car in for something else and while it was there they pressure tested the cooling system. it held pressure for the hour that they tested it. the next day (before i could replace the bypass hose) the leak stopped. hasn't happened since. wonder if it was somehow related to the fact that the two days it leaked were the only two really cold days/nights so far this year.
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