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Coolant leak (300m 3.5L) - what could be source?

Discussion in 'LH: Large Cars, 1993-2004' started by MoPar~Man, Dec 29, 2019.

  1. MoPar~Man

    MoPar~Man Member

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    For the better part of the past year, my '00 300m has been leaving about a teaspoon of coolant on the garage floor overnight on most days. A few days ago I finally got around to replacing what I thought was the source - the upper rad hose (I thought the leak was happening at the top end of the hose where it connects to the engine). Turns out this is not where the leak is coming from. From under the car, I can see some drip points on the back-edge of the sub frame and the front edge of the oil pan (not sure how it can drip from both locations given the air-gap between them). All rad connections look clean and dry, as does the upper rad connection. So what gasket or seal could be causing this?
     
  2. ImperialCrown

    ImperialCrown Moderator
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    Leaks will usually blow back and down from road draft and gravity. Turbulence under the hood can blow it around and be misleading as to the source.
    The water pump under the front cover is a common leaker. It is driven by the timing belt.
     
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  3. valiant67

    valiant67 ...

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    But, rent, or borrow a coolant system pressure tester. You’ll be able to trace the leak better than finding after the car has driven and some evidence of the trail may have evaporated.
     
  4. chuzz

    chuzz Well-Known Member

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    Sometimes a loose hose clamp can drive you crazy. I'd check all of them too.
     
  5. MoPar~Man

    MoPar~Man Member

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    I had the timing belt and water pump changed back in I think it was 2012, at a chrysler dealership, and I asked for the old pump and belt so I'm reasonably sure the work was actually done. So I've never seen myself what it looks like behind the timing belt cover but in looking at the manual and the videos it seems that that area is sealed off from the oil sump so it should be bone dry. My first question is:

    If the water pump gasket / ring leaks, where does the coolant go? Is there an escape path from the timing belt area?

    Second question: The thermostat housing and the lower rad hose connection (and the other smaller pipe coming off the other thermostat housing where another hose is connected to) is hard to see. Is this the likely area for the coolant leak?

    Between the water pump o-ring and the thermostat housing (and the connecting hoses) where else would the coolant leak from and drip from somewhere at the front of the engine? A head gasket?
     
  6. Tomguy

    Tomguy Well-Known Member

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    There are a few possibilities. However, based on your description, I'd start with the heater line off the thermostat housing. Is the rubber leaking there? Maybe from the clamps? Also, the hard metal line itself is susceptible to corrosion. Maybe it's starting to rust through.

    OTHER Possible sources:
    • Radiator - The plastic side on my original cracked at about 15 years, the first aftermarket replacement lasted about 2 years, the second is ok so far.
    • Radiator hoses - Yes, you did the upper hose, but did you use a scouring pad on the manifold's outlet? If it has corrosion on it, it can still leak easily. The lower hose connects at the T-stat housing, and can leak.
    • Radiator cap - Look for leaks around the cap on the coolant overflow reservoir.
    • Overflow reservoir (and the upper and lowe lines to it) - The left side is pressurized, 16PSI. The right is not. If leaking out the right overflow you either are overfilled or boiling over, or have a bad radiator cap. The unit is plastic and probably can crack with age. I'd make sure that lower hose connection isn't cracked.
    • Thermostat housing/gasket - Unless you recently did this job, and the gasket isn't tight, I wouldn't suspect this itself as the cause. The housing could in theory corrode but it's pretty thick and heavy-duty, so I really really doubt it.
    • The hoses to the heater core itself - these connect by the back of the engine at the firewall, but run close enough to the engine that it could drip down off the front.
    • Water pump - Just because it was done 8 years ago doesn't mean it's not bad. Yeah, they wear out with miles, but short trips and sitting are just as hard on them, if not worse on the seals. The leak could appear anywhere around the timing cover depending on if the timing belt or its turbulence is tossing coolant around. When sitting, it's most likely to come out of the front by the crank snout, the small timing belt cover piece on the bottom shaped like a "U" held on with 3 bolts.
     

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