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  #46  
Old 06-25-2006, 10:05 AM
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Location: Blue Point, NY
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Quote:
Originally Posted by JDmills
Yes. every time, I thought that this was a quick and dirty way to prevent air bubbles in the head... Wrong again Jason..
As I think about this again, I think you are right. How about the thermostat vent hole in the themostat housing. It it just two streight lines/passages that are connected and diverge at about 110 degrees? I think the thermostat housing is more involved than I gave it credit for.. will check the bypass elbow and report back..
Try one other thing.........

After you start it and run it........and the temp climbs up to 100°C..........let it cool again.........and fill the upper hose again..........there is likely to be air trapped at the top of the cylinder head. A single fill will usually fail to displace this air.

Repeat this process until no air is found in the upper hose when you remove it from the radiator.

Sometimes they get air at the top of the system and won't give it up.

I checked out the FSM. The small line between the pump and the head is a vent line of some fashion.

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  #47  
Old 06-25-2006, 10:27 AM
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Air bubble.

I recently did an auto/manual climate control swap. Obviously, I had to drain the coolant. When I refilled the coolant I got an air bubble below the thermostat ('79 300D, so slightly different thermostat housing). Sitting at idle, the temp. didn't stop at 100C, it went straight to the top of the gauge. If the thermostat were stuck closed, your car would overheat. Quickly.

Jay.
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  #48  
Old 06-25-2006, 01:16 PM
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Quote:
Originally Posted by Brian Carlton

After you start it and run it........and the temp climbs up to 100°C..........let it cool again.........and fill the upper hose again..........there is likely to be air trapped at the top of the cylinder head. A single fill will usually fail to displace this air.


GOOD Idea. Never would have thought of that! will check it before even touching the vent bypass.
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Last edited by Brian Carlton; 06-25-2006 at 01:25 PM.
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  #49  
Old 06-26-2006, 04:17 PM
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Well, yesteday afternoon was a productive day for the 300TDT.

pulled the water pump bypass elbow off, it was clean/clear and in no way causing my issues.

Went and studyed the termostat housing, to understand how the termostat worked, and had how the coolant flowed when the thermostat was closed vs, open. studyed the old thermostat, studyed the new thermostat. Put the old thermostat in and refilled the block. Actually I filled the whole cooling system via the upper radiator hose where it goes into the block. The difference being that I took 20 minutes to allow the head/block to 'burp' half a dozen times.
Went and rebuild the rear brakes. Returned to add more coolant to the upper radiator hose. ( in the past it was just a 'fill it until it was full, attach to radiator, and test drive)
Topped off the expansion tank with about a quart of coolant, and went to bed.

Today, the tempature gage did not go past 80'C. put about 10 miles on the car, and in fact the tempature dropped from 80'C to 78 or so, on the down hill leg of the trip.. So the mistake I made was: changing the thermostat and burping the block/head at the same time, will never know 'what' was the true cause of the extended tempatures, But then I am gland to be through the process, and hopeful to know how to avoid the problem in the future.

May have caused a leak in the heater core, as the car smells of antifreeze with the heater on.. has done so in the past, but never had to add coolant so it was a moot issue. Hopefully it will be the same now. Thanks for all your ideas, perspectives, and thought provoking questions. would not have devoloped the understanding of how this cooling system works with out all that help. Hope fully I can return the favor some day in the future, in some smalll way.
Jason
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  #50  
Old 06-26-2006, 05:49 PM
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Quote:
Originally Posted by JDmills
Actually I filled the whole cooling system via the upper radiator hose where it goes into the block. The difference being that I took 20 minutes to allow the head/block to 'burp' half a dozen times.
Went and rebuild the rear brakes. Returned to add more coolant to the upper radiator hose. ( in the past it was just a 'fill it until it was full, attach to radiator, and test drive)
Topped off the expansion tank with about a quart of coolant, and went to bed.

Today, the tempature gage did not go past 80'C. put about 10 miles on the car, and in fact the tempature dropped from 80'C to 78 or so, on the down hill leg of the trip..
Excellent job. We knew it was a flow issue with the thermostat not seeing the actual coolant temperature in the head. I must say, however, that your engine is definitely one of the more difficult ones that I have seen. That's good info for others who can't seem to get the temps to stabilize.

My SD simply required filling the upper hose once.........and adding some coolant over the next several days.

Glad you got it fixed without spending a bunch of money on fan clutches, auxiliary fans.........etc.
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  #51  
Old 06-26-2006, 08:48 PM
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Quote:
Originally Posted by Brian Carlton
Excellent job. We knew it was a flow issue with the thermostat not seeing the actual coolant temperature in the head.
Brian, You were very consistant about the thermostat/flow issue. Which was a big help in keeping me focused on the symptoms, and working the problem. Thanks again
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Last edited by Brian Carlton; 06-26-2006 at 09:24 PM.
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  #52  
Old 06-26-2006, 09:25 PM
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Quote:
Originally Posted by JDmills
Brian, You were very consistant about the thermostat/flow issue. Which was a big help in keeping me focused on the symptoms, and working the problem. Thanks again
Anytime.

Help is what we do here.
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  #53  
Old 06-27-2006, 06:00 PM
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Join Date: Apr 2006
Location: Birmingham, AL
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Quote:
Originally Posted by JDmills
Well, yesteday afternoon was a productive day for the 300TDT.

pulled the water pump bypass elbow off, it was clean/clear and in no way causing my issues.

Went and studyed the termostat housing, to understand how the termostat worked, and had how the coolant flowed when the thermostat was closed vs, open. studyed the old thermostat, studyed the new thermostat. Put the old thermostat in and refilled the block. Actually I filled the whole cooling system via the upper radiator hose where it goes into the block. The difference being that I took 20 minutes to allow the head/block to 'burp' half a dozen times.
Went and rebuild the rear brakes. Returned to add more coolant to the upper radiator hose. ( in the past it was just a 'fill it until it was full, attach to radiator, and test drive)
Topped off the expansion tank with about a quart of coolant, and went to bed.

Today, the tempature gage did not go past 80'C. put about 10 miles on the car, and in fact the tempature dropped from 80'C to 78 or so, on the down hill leg of the trip.. So the mistake I made was: changing the thermostat and burping the block/head at the same time, will never know 'what' was the true cause of the extended tempatures, But then I am gland to be through the process, and hopeful to know how to avoid the problem in the future.

May have caused a leak in the heater core, as the car smells of antifreeze with the heater on.. has done so in the past, but never had to add coolant so it was a moot issue. Hopefully it will be the same now. Thanks for all your ideas, perspectives, and thought provoking questions. would not have devoloped the understanding of how this cooling system works with out all that help. Hope fully I can return the favor some day in the future, in some smalll way.
Jason

rebuilt rear brakes fixed it!!!


just kidding!!! i''ve been watching this thread from the very beginning, and i'm glad that you've finally fixed the problem! i'm proud of you!!!

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