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  #1  
Old 02-28-2003, 06:26 PM
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Wierd coolant leak issue

Okay, for several weeks now my '84 300D has been developing small leaks at what seems to be every hose clamp connection. I have chased them all tightening all clamps I can find. In fairness some were quite loose by my standards. I noticed that the cooling system seemed to retain some pressure overnight or even over a few days without use. Not much pressure but enough to hear it "hiss" when the cap is opened. I replaced what appeared to be an original rad cap with a "Motorad" brand cap and the problem has persisted. Today I grabbed my ankles and purchased an MB cap from the local dealer for a ridiculous $26. I hope they enjoyed having their way with my wallet.... I have checked the hose clamps again, all are tight. The coolant loss is very small, like spots the size of a quarter when they occur. I can't explain the retention of pressure in the system overnight. I have heard this is evidence of a bad head gasket or cracked head but I have a really hard time believeing that as the engine runs so good, uses little oil and besides the tiny leaks, no coolant. Any ideas or am I chasing shadows here? Thanks, RT

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  #2  
Old 02-28-2003, 06:39 PM
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A head gasket is definitely a possibility...can't think offhand of anything else that would put enough pressure on the cooling system to keep it under pressure for that long of a time...

Have you done a cylinder leak-down test?
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Old 02-28-2003, 06:49 PM
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rw - I would recommend just keeping the fluids at the proper level and live with it. It does sound like either a head gasket or cylinder head issue.
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Old 02-28-2003, 08:30 PM
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I love a good mechanical mystery....

first... YOUR leaks should have Nothing to do with any head gasket problem because if you have a LOT of pressure your radiator cap should provide an escape for it.... your hoses should hold any and all pressures under the cap limit... and the cap usually decreases in pressure over time.

so I am down to a couple of items....

1. How old are your hoses ?

2. When you put them on did you use any gasket sealer ?

3. Did you use anything else ( like god forbid petroleum grease)?
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Old 02-28-2003, 10:23 PM
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Thanks for all the replies! I love a good mechanical mystery myself. This issue doesn't worry me as much as it makes me REALLY REALLY curious. I'm one of those people that just has to know how, when, where, why, etc. I agree with Leathermang. The cap should release any excess pressure so there is little chance of the cooling system being subjected to any undue stress. The hoses are of unknown age, they came on the car. They are in very good condition and since I know the car was maintained very well I suspect they were done recently. I did change the coolant to Rotella ELC so maybe that is a factor but I can't see how it would be. Besides the leaks started almost two months after the change. Since it was a southern car I am also wondering if maybe the severe temperature swings of this especially cold NE winter has caused the hoses to loosen up a little. I can certainly live with it since it doesn't use/lose any fluids and runs great. RT
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Old 02-28-2003, 11:23 PM
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On the very coldest nites several small leaks have developed on my 300D as well. In a couple of instances the clamp in the area was tightened a tiny bit. In a couple of cases when it got markedly warmer the leaks disappeared. Suspect it is mostly related to much lower than usual temps and hoses that could be a little on the aged side.
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Old 03-01-2003, 07:32 AM
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rwt, i have noticed with my car almost every year after the first freeze it leaks some coolant from somewhere. this year was the bypass hose under the t-stat housing. put a couple of new clamps on and tightened 'em down hard and it went away. i think it had a lot to do with the extreme low temps as when the engine warmed up the leaks stopped.
if you're not losing massive amounts of coolant i believe warmer weather will automatically improve the situation for you.
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Old 03-01-2003, 11:11 AM
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The next time you change hoses... use aviation gasket cement on their insides when you install...that should negate any slight hose clamp tension differences or whatever is happening.
I will bet that would keep any of this from happening.... yes, the next time you want to change them you probably will have to cut them off... but I usually do that anyway because it is fast and I don't reuse them....

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