84 300TDT cooling system questions - Page 2 - PeachParts Mercedes-Benz Forum

JDmills · #16 06-17-2006, 06:57 PM

I might go at it right now, as it has been cooling down for about an hour or so. I hope to see a really rusty impeller...

JDmills · #17 06-18-2006, 09:26 PM

Quote:

Originally Posted by Brian Carlton

I'm really hoping, however, that there is corrosion on the pump vanes and the flow is inadequate due to this. The only thing left is more corrosion in the block and head.........necessitating another citric acid flush.

So was I!! and disapointed to find that the Pump impeller looked good... that is no a bad job, I expected it to be more difficult than it was.
Next on the list: Where is the tempature sending unit? I see three sensors on the head that could be the sending unit. One on the thermostat housing, one below the #2 cylinder injector , and one below the #3 cylinder injector. I guess it would be silly to test the tempature gage now, but it will rule that variable. Starting to worry that a citric acid flush will not be enough to cure this problem.. but I guess I should not get ahead of myself.

Motorhead · #18 06-18-2006, 09:46 PM

Have you checked to see if your AIR CONDITIONING condensor fins are plugged up with bugs? It can block air flow through to the radiator.

JDmills · #19 06-19-2006, 11:17 AM

I removed the condenser a few days ago. As the compressor has been sitting in the barn for over a year... But my issue seems to be a lack of coolant flow comming out of the block/head. Wondering today if removing the thermostat(temporarily unitl all flushing, and cooling system work is completed) would improve the chances of restoring the volume of water flowing through the block.. any opinions on that tatic?

Motorhead · #20 06-19-2006, 12:37 PM

NO..... DO not remove thermostat and run the car. It will deffinately overheat. The thermostat also works as a diverter to seal off a passage that makes it circulate through the radiator. Apparently when the engine is cold, it works to let the coolant circulate in the engine only. Thats why our cars warm up so fast.
I would REPLACE the thermostat with another new one.

newagon · #21 06-19-2006, 01:31 PM

it sounds like you're way ahead of me in troubleshooting your cooling system, but thought i'd offer that my 82 300td does the SAME thing. i had the radiator checked out (supposedly its fine. I'm not a mechanic, so i have to have other people do this stuff for me. i'm trying to learn stuff here!) and had the thermostat replaced. car still runs hot (90-105) especially going up hills and if i have the AC on. if i'm going up a long grade (like the Grapevine here in LA where I live) it gets close to 115 and i have to pull over and let it cool down. i see so much on this forum about 100 being still in the normal range, but every now and then when i pull over even at 100, i hear the hoses bubbling.
anyway, not much help from a non-mechanic, but affirming that this seems to be a recurring issue with the 300td's
i'm following your thread and hope you solve it!

JDmills · #22 06-19-2006, 04:52 PM

Moterhead, I was not thinkin of running the car with out the thermostat, (driving in daily use, but wondering If a thermostat free engine would put more coolant through the block and head..) I have the feeling that there is a coolant flow issue, so I am trying to minimize any restrictions in the system... thus when the next batch of citric acid shows up on wednesday, there might be chance of getting the block cleaned up again.

Newwagon, I dont know what I am doing. Just trying to test all the variables and find what that leads me to next. I don't think that a cooling system that runs above 95 is healthy, and vital, so you may have some issues to look into. That being said I have never driven in the desert at 110' in the full sun so may be a cooling system that shows 110 centegrade under those conditions is working just fine...

Brian Carlton · #23 06-19-2006, 06:58 PM

I've been mulling this problem over for the last 24 hours and definitely find it baffling.

Just to summarize, we have a new radiator, new thermostat, thermostat checked in a pan of boiling water, no condenser, water pump impeller in good condition.

If the coolant is flowing properly in such a system, it cannot get over 90°C. or so.

I also find it difficult to believe that the passages in the head or the block are so restricted as to prevent sufficient coolant flow..........although I can't rule it out.

But, one possibility that I do see is the potential for the thermostat housing to be holding some trapped air. If this occurs, then the thermostat won't ever see the actual coolant temperature and will never fully open.

So, two things come to mind.

1) Remove the thermostat and drive the vehicle........for testing purposes only. I don't expect the vehicle to remain in this condition, however, if more coolant flows to the radiator and the temperature does not climb quite so high, then we can say that we are on the right course.

2) The thermostat housing has it's own internal vent line. The line is quite small in diameter and it shares the casting with the main line that goes to the radiator. See if you can find this line on the housing and verify that it's not blocked. The line makes a 110 degree turn from the back of the thermostat out toward the radiator. It's got plenty of capability to clog on this turn. If it's clogged, the chances are good that the housing can't vent itself.

Report back on what you find.

Take careful note of the temperatures at various operating points. Remember, we are not looking for it to stay below 90°C..........just hoping that it doesn't climb as high as it did before.

JDmills · #24 06-20-2006, 10:28 AM

Brian,
Your trouble shooting skills are impressive, especially in light of taking all information in second hand. Thanks for taking an interest in this thread. Your insight as to a air locked thermostat, seems to be getting us closer.

I have not had enough time to test drive the car, but was able to see that the coolant flow through the radiator is much improved, after taking the thermostat out. I am not celebratiing yet, but is is nice to be able to let go of the fear that the block/head passages are plugged in some way. tomorow will be my first opportunity to explore the (air bleed passage in the thermostat?) and take the car for a test drive. Hope to be able to report back more positive news.
Jason

Brian Carlton · #25 06-20-2006, 12:18 PM

That is welcome news.

I'll be real interested to see what its temperature will be at various operating points........hopefully, the increased flow will keep it relatively normal, even with the loss of coolant to the bypass.

If this occurs, then we must pursue the venting of the thermostat.

JDmills · #26 06-21-2006, 07:40 PM

Yeah Hooo!

Went for a test drive, W/out thermostat.. saw a high of 70'C. Which was climbing a 3 mile hill at about 40 Mph. on the down hill trip the temptature dropped to about 55-58.

I guess that indicates the themostat (housing?) is a part of the issue? will be doing another citric acid flush may be tomorow, and will try and send some compressed air through the vent hole to see if it is plugged..

All of which makes me wonder why the termostat was getting air bound late this spring, would have thought that the air in the system would have been purged over the course of the winter... Not a head gasket? But will a healthy engine tend to produce air pockets, in normal use... I guess if the vent tube is plugged It might produce irregularitys?? only if there is air getting stuck behind the thermostat...

Brian Carlton · #27 06-21-2006, 09:24 PM

Quote:

Originally Posted by JDmills

Yeah Hooo!

Went for a test drive, W/out thermostat.. saw a high of 70'C. Which was climbing a 3 mile hill at about 40 Mph. on the down hill trip the temptature dropped to about 55-58.

I guess that indicates the themostat (housing?) is a part of the issue? will be doing another citric acid flush may be tomorow, and will try and send some compressed air through the vent hole to see if it is plugged..

All of which makes me wonder why the termostat was getting air bound late this spring, would have thought that the air in the system would have been purged over the course of the winter... Not a head gasket? But will a healthy engine tend to produce air pockets, in normal use... I guess if the vent tube is plugged It might produce irregularitys?? only if there is air getting stuck behind the thermostat...

Well, we definitely confirmed that the issue is a flow problem past the thermostat. And, since the thermostat has definitely been checked and is functional, the only remaining possibility is air that is preventing sufficient coolant from fully opening the thermostat at the desired temperature.

Normally, the air will eventually purge itself over time, however, that vent line from the thermostat is a rather sophisticated setup and, if it's plugged, you can bet there will be issues with trapped air that won't clear.

I'll be curious to see what you find with that vent line.

Motorhead · #28 06-21-2006, 11:03 PM

JD, After you get the bleed hole issue checked out, drill a small 1/16th hole in the outer stationary part of the thermostat. Position this hole towards the top.

JDmills · #29 06-22-2006, 09:22 AM

Motorhead, That thought went through my mind, But I want to see If I can get it back to stock and efficent operation first... Then we can modify and improve as necessary.

Motorhead · #30 06-22-2006, 04:37 PM

JD, Good idea..... I just do that with ALL thermostats. I find that I don't get the fluctuations on temp by doing that. Let us know!!