83 300SD Thermostat help? - PeachParts Mercedes-Benz Forum

83w126 · #1 03-21-2013, 12:32 AM

I replaced the thermostat, and the new one doesn't open. Is it just becasue I broke the #1 rule of working on german cars (that its cheaper to just buy the factory part to begin with, than both an aftermarket part and a factory one to replace it when it doesnt work), or did I do something else wrong?

Also, the cooling system has not held pressure since I have had the car, but only had one visible leak that just started recently, which I fixed today. But, it still doesn't hold pressure. Are there any likely places to check for invisible leaks? It does not loose coolant, have any visible leaks (anymore) or normally run unusually warm, but on an very long and steep grade I have to slow down to 45 mph to keep it from overheating. The cooling system works fine for where I normally drive, but I would like to get it to work as it was intended.

weird beard · #2 03-21-2013, 12:50 AM

I had an issue with mine getting an air lock in the upper rad hose. Had to fill the hose from the rad side to get the coolant to push through.

Diesel911 · #3 03-21-2013, 12:55 AM

Tiny leaks can be anywhere in the Coolant System; even the Heater Core or into the Cylinder.
The more normal places for leaks is any place there is a Hose; next would be Gaskets and the Core/Freeze plugs.

I violated a rule I used to follow of testing the New Thermostat Suspended in a Pot of water (a tsp of Salt reduces the Bubbles) and heat the Water up as you observe a thermometer (You can use Meat or the less expensive Glass Candy Thermometers) so you can see when the Thermostat opens.

I did not do that and of course the New on opened too late at a temp too high and I had to go through the Mess of Draining The coolant again (not on a Mercedes).

I have seen tiny Pin Hole type leaks on Metal Parts that where never wet but you could see a white or greenish build up around the Hole.

When I changed the large short Hose Coolant Hose close to the EGR I found that under the Hose area the Aluminum was all eaten up and corroded.

83w126 · #4 03-21-2013, 01:00 AM

Hmm, so just forget it on getting the air leaks to stop? With how complicated the cooling system is I could see it being an impossible job. I was thinking about drilling a small hole in the thermostat too, that would help with air bubble problems I think.

cho · #5 03-21-2013, 04:06 AM

.

drilling holes would not help you,in older t-stat housing it might,but
in 83 SD nope,you have to find where and why you loose pressure.

it may be simple as overflow jar cap (if you have one) or radiator cap.
did you try to squeeze upper radiator hose on cold and on warm?

did you burp system properly?

however testing t-stat before installation as described by diesel911
is highly recommended.

cheers

.

cho · #6 03-21-2013, 04:12 AM

Quote:

Originally Posted by weird beard

I had an issue with mine getting an air lock in the upper rad hose. Had to fill the hose from the rad side to get the coolant to push through.

that one always helps

BTW, I'm interested do you have coolant expansion tank?

.

vstech · #7 03-21-2013, 09:29 AM

83 should have the tank, if it's a turbo motor (euro's are often N/A, even in 83) on mine, there were cracks in the expansion tank that kept it from building pressure. I also have one where the neck of the expansion tank would seep pressure out. none of mine actually overheat though.
if your dash gauge is hitting the red line, then you might have several other problems.
1st, is the engine ground SOLID to the car?
2nd, are you sure the temp gauge/sender is not faulty? IR thermometers are wonderful for this.
3rd... hate to say it, but yeah... german t-stats are the way to go here...
4th ya need to park the car REALLY HIGH nose up, to get these cars properly filled with coolant, and the monovalve can cause the system to hold air as well.
... again, hate to say it, but head gasket is the next logical thing to test...

eatont9999 · #8 03-21-2013, 11:30 AM

If the thermostat is not Behr branded, it does not belong in the car.

The correct thermostat should have a bypass hole in it already. The likely cause of your loss of pressure is the expansion tank. I had to replace mine because it had hairline cracks that would lose pressure but not obviously leak coolant.

Govert · #9 03-21-2013, 12:03 PM

The thermostat housing has a bypass channel on the later models (1979 switchover year I think), the thermostat has none. The thermostat for earlier models without the bypass channel (yes, there are several models) had a bypass hole.

qwerty · #10 03-21-2013, 01:34 PM

Quote:

Originally Posted by eatont9999

If the thermostat is not Behr branded, it does not belong in the car.

Do you have data to support that claim?

I could fill a short bus with folks who have had less trouble with Wahler thermostats than they have with Behr.

Quote:

Originally Posted by eatont9999

The correct thermostat should have a bypass hole in it already.

The thermostat housing in the subject vehicle would feature a bypass integral to the thermostat housing, rendering a bypass hole in the thermostat itself totally and completely useless.

Brian Carlton · #11 03-21-2013, 08:04 PM

Quote:

Originally Posted by 83w126

I replaced the thermostat, and the new one doesn't open. Is it just becasue I broke the #1 rule of working on german cars (that its cheaper to just buy the factory part to begin with, than both an aftermarket part and a factory one to replace it when it doesnt work), or did I do something else wrong?

I'll make a gentleman's bet that the new one opens fine.

Remove the upper hose and fill the head with coolant right to the top of the hose. Reinstall the hose on the radiator.

Magically..........the thermostat is fixed.

83w126 · #12 03-21-2013, 08:46 PM

Quote:

Originally Posted by vstech

83 should have the tank, if it's a turbo motor (euro's are often N/A, even in 83) on mine, there were cracks in the expansion tank that kept it from building pressure. I also have one where the neck of the expansion tank would seep pressure out. none of mine actually overheat though.
if your dash gauge is hitting the red line, then you might have several other problems.
1st, is the engine ground SOLID to the car?
2nd, are you sure the temp gauge/sender is not faulty? IR thermometers are wonderful for this.
3rd... hate to say it, but yeah... german t-stats are the way to go here...
4th ya need to park the car REALLY HIGH nose up, to get these cars properly filled with coolant, and the monovalve can cause the system to hold air as well.
... again, hate to say it, but head gasket is the next logical thing to test...

I have never let it get more than 2/3 of the way up on the gauge, but I dont feel like I should keep my foot down going up a steep hill when the temp gauge starts rising quickly and I know the cooling system isnt quite right. It never gets above the 80 mark on flat ground though. I dont even know where the engine ground is, but I have no reason to believe the temp gauge is wrong from the way it behaves normally. And I did already order a german thermostat. It would be over $400 to completely rebuild the cooling system with all factory parts, so I don't plan on just replacing everything if some of it is likely still fine.

vstech · #13 03-21-2013, 10:25 PM

if the thermostat holds around 80 on normal driving, then I'd say the ground is not the issue, not the thermometer gauge or the sender either.
what condition is the radiator and condenser in externally?
i like to pull my radiator and aux fan, so I have total access to the condenser to remove bugs, and straighten fins, also get the coil chemically clean so it has the best heat removal for the a/c, and while I have the radiator out, I like to soak it in coil cleaner as well. get the fins REALLY BRIGHT and remove all bugs and such from the air stream.
next I'd verify the fan clutch is working correctly, and verify the engine fan is the plastic one you are supposed to have with the 83. also, note if the shroud is intact and present, and that you don't have slipping belts.

weird beard · #14 03-22-2013, 04:31 AM

what year did they change the water pump pulley size? if it has the larger earlier pulley, it could be swapped for the newer smaller one and increase the water pump speed. Just a thought.

Cleaning the rad gets my vote as well

vstech · #15 03-22-2013, 07:10 AM

83 SD should have the smaller pulley, and plastic fan. check what size your belts are. 1035 is the large pully, 1000 or 975 would be the small pulley.