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  #16  
Old 04-12-2007, 08:25 PM
Craig
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Quote:
Originally Posted by sleeeper View Post
I appreciate the help but I don't think I'll be starting there for practical reasons. The current radiator worked fine until recently and is a high quality replacement. Again, this is a new problem not coincident with the installation of the radiator. I may explore a way to disable the lower gasket on the radiator cap to return it's function to that of the stock radiator. but none of that would explain the overpressure problem directly.
That may be a good idea, and I do think it could explain the level issue in the tank. If you modify the cap, I would be curious to hear if it helps.

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  #17  
Old 04-12-2007, 11:45 PM
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Turbocharged OM616 Diesel
 
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Location: Albuquerque,NM
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Hi Sleeper,

Well I'm happy to hear (read?!) that the car passes the blown HG test.

This is going to seem like a really stupid question, but was the new thermostat physically identical to the old one? I know on my 240 there is a small disc on the back (engine side, not radiator side) of the thermostat that closes off the bypass circuit as the thermostat opens. If the disc is missing (wrong thermostat) then the engine will run hot because it is recirculating coolant internally rather than pumping it through the radiator. This would explain your symptoms.

Good Luck, Chris
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  #18  
Old 04-12-2007, 11:52 PM
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Thats actually a good question, but the thermostat was the right one, I was very carefull when installing it.
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  #19  
Old 04-13-2007, 01:22 AM
1984 300SD
 
Join Date: Feb 2007
Location: Vancouver BC
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Hose lining problem

The small hose from the rad to the resevoir may have a lose inner liner that is seperated from the woven section. That will act like a check valve under pressure but appear to be clear when removed. A new hose is couple of buck or so. I had this problem last year, went nuts checking things. I got this tip on the board.
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  #20  
Old 04-13-2007, 06:19 AM
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Exclamation Just a bit of info.....

If you have access to the MB Engine Service Manual.....section 20-005 has a nice diagram of the cooling system "as designed"........

AND....if you installed an OEM thermostat....it has a little arrow on it's edge....this arrow points up.......

SB
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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG
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  #21  
Old 04-13-2007, 11:47 AM
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Quote:
Originally Posted by sleeeper View Post
there are two small hoses, one between the upper part of the radiator filler neck and the side of the resevoir tank itself, and one that attaches to the side of the overflow resevoir filler neck that drains to the road. The first one only comes into play when the lower seal of the radiator cap is opened via pressure as in this picture: http://www.centuryperformance.com/images/tech/radcap.jpg . This has been the arrangement from both before and after this problem started. On my car the radiator and the resevoir both have caps and the radiator is an all metal replacement unit that was already installed when I bought the car. It has worked well in this configuration for at least the last 20k miles without causing the problems I am seeing now.
Sounds like an air bubble. Expands when hot, forcing coolant into the reservoir tank. Reservoir cap bleeds pressure off to make room for coolant. Air bubble contracts when cool, but can't suck coolant from the reservoir due to its trapped negative pressure so a hose collapses instead. Open the radiator cap allows air into reservoir and radiator, equalizing pressures, then gravity brings the coolant back into the system.

That's only a theory. It should be easy to see if this is what's really happening. If it is, then one of the radiator hoses is probably collapsing until you open the rad cap. More likely to be one of the bigger ones, so should be easy to spot.

Disabling the rad cap's lower gasket will allow the coolant to flow back and forth freely, but won't get rid of the air bubble.

The system wouldn't have done this unless you had an air bubble in it, so maybe it didn't have one before but does now.
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  #22  
Old 04-13-2007, 12:04 PM
AHH,What's up Doc????
 
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Quote:
Originally Posted by sleeeper View Post
I appreciate the help but I don't think I'll be starting there for practical reasons. The current radiator worked fine until recently and is a high quality replacement. Again, this is a new problem not coincident with the installation of the radiator. I may explore a way to disable the lower gasket on the radiator cap to return it's function to that of the stock radiator. but none of that would explain the overpressure problem directly.
It sounds like you increased the coolant to water strength to a higher concentration than before. Coolant/antifreese will increase pressure and temperature at coolant concentrations greater than 70%. Unless your in a really cold climate, a mixture at 50/50 is usually best!
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  #23  
Old 04-13-2007, 05:12 PM
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The last two posts sound like they are right on the money, I never knew that about coolant concentrations before, and I may have done just that. I will try again to bleed the air.
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  #24  
Old 04-14-2007, 06:59 AM
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Not exactly.....

Quote:
Originally Posted by Knightrider966 View Post
It sounds like you increased the coolant to water strength to a higher concentration than before. Coolant/antifreese will increase pressure and temperature at coolant concentrations greater than 70%. Unless your in a really cold climate, a mixture at 50/50 is usually best!
Your coolant (whatever the mix) absorbs heat from the engine block, and transfers it to the atmosphere via the radiator.....if all parts of the system are operating "as designed" then there should be no difference in operating temperature and pressure......

The pressure within the cooling system is controlled by the "Pressure Cap"......and is unaffected by the coolant.......it will relieve excess pressure, only.......thus maintaining a maximum allowable pressure within the system......

SB

I went back and re-read the original post.....your radiator cap is designed to allow excess pressure to vent from the cooling system, but it also should allow atmosphere back into the system as it cools......check your radiator cap!!!......sounds as if it's not allowing atmosphere back into the system, thus forming a vacuum within the system when cooled.....
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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG

Last edited by Shorebilly; 04-14-2007 at 07:06 AM. Reason: additional commentary
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  #25  
Old 04-14-2007, 07:49 AM
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Question

Quote:
Originally Posted by Bio240D View Post
Thats a Head Gasket!

Here is a simple test. Take off the rad cap, fill system with coolant, Leave the rad cap off and crank the engine, but don't let it start (just crank immediatly rather than letting the GPs get hot first). If the HG is blown, coollant will shoot from the radiator in strong pulsing spurts. This could also mean a cracked head or block, but that's pretty rare.

Sorry to be the bearer of bad news, but I went through this with a blown HG on my 240D. Identical symptoms, but I hope I'm wrong!

Good Luck, Chris
on your 240d was there any oil in the coolant or coolant in the oil?

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