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Discussion Starter #1
I just read the STAR CD for the thermostat replacement procedure for the CDI, and it seems straightforward. (As straightforward as it can be without actually starting to get into it).

The coolant re-fill procedure lists the use of some vacuum assisted re-fill device that uses a special test cap used on the expansion tank. Is this vacuum fill device actually needed, or can one just fill the system thru the expansion tank?

Thanks.
 

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Fill

That would be something good to know if I got in there one day and drained the engine. It would be hard to believe you just could not fill it and then run it filling it again when needed looking at it.
 

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Discussion Starter #3 (Edited)
That would be something good to know if I got in there one day and drained the engine. It would be hard to believe you just could not fill it and then run it filling it again when needed looking at it.
That is what I would think also, but the prodecure does specify the vacuum fill device (has a MB part number, I'll have to look at home again for the PN). Just wondering if the vacuum device is used for expediency at the dealers, or if it truely is necessary to properly fill the system.

I wonder what the dealer is going to charge for a thermostat change? I'd bet $500-$700.

I'd think someone here has drained and re-filled a CDI by now. Bueller? Anyone?
 

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I drained and re-filled it, didn't use any special tools...there is a hose that goes from coolant system to top of coolant tank that will allow air to escape during fill ups... also changed thermostat on my own...needed to thread a few holes on thermostat , other than that it's a very simple procedure, just unscrewing a few bolts and putting it together...
 

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Discussion Starter #5
I drained and re-filled it, didn't use any special tools...there is a hose that goes from coolant system to top of coolant tank that will allow air to escape during fill ups
Great. So I assume that hose where it enters the tank must be the highest point in the system.

... ...needed to thread a few holes on thermostat
Meaning you had to run a tap thru some holes? That seems quite unusual to have to tap holes in a replacement part. MB part or aftermarket?
 

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Soooo..

To anyone who has had this procedure done I have a few questions:

1) Did your fuel economy return to the summer levels?
2) How much faster did your car warm up and what was your highest temp?
3) Did you run this new thermostat in the summer and if you did what state are you from?
4) If you didn't run it in the summer, when did you take it out?


I'm contemplating the change but I only see a 10% change in efficiency so the amount of time to recoup my costs may be too long..

Thanks all in advance!!
 

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In winter fuel economy didn't return to summer levels and it's dumb to expect that.
Car didn't warm up any faster.
Ran it in the summer and now in the winter.

All my thermostat did is allow the car to warm up to 92C instead of 82C... my fuel economy improved and car is running somewhat more efficient (thus improved fuel economy), it's not good for engine to never warm up.
 

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Discussion Starter #9
I'm contemplating the change but I only see a 10% change in efficiency so the amount of time to recoup my costs may be too long..
I have not changd mine out yet, maybe this weekend if the parts come in. My car is only warming to about 70C, and that is just not good enough.

The cost/benefit analysis should not be "does this thermostat change pay back in fuel savings", but shoud be "does this thermostat change preclude potential future expensive engine repairs."

Engines running this cold are not running at design temperatures, oil is not at spec viscosity, any number of parameters are not at normal design points. I speculate that extended operations at these temps are not good for the engine and systems.
 

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Well, I'm taking the plungs and changing the thermostat this weekend!! It was cold here in NC and the engine warmed up to 60 and stayed there for the 30 mile drive. This engine is definitely not performing to design specs and the temperature is way too low..

I'm thinking maybe 45 minutes to drain maybe half of the coolant and replace the thermostat and filling back in the top of the reservoir..

Wish me luck..
 

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Good luck Aeubank! I did mine a couple of weeks ago. Mine CDI seemed to take a long time to get up to 80C, and last winter it seemed to fluctuate below 80C. The one I installed is 92C. The car does not warm up any faster, but I know that diesels like to run hot for efficiency.
I did not drain any antifreeze out, I just removed the radiator and bypass hoses and let the antifreeze run out. When I removed the thermostat housing, some additional antifreeze ran out. Just make sure that you cover the oil filter hole as you have to remove it to remove the thermostat. Starting the car back up I think that I put in almost a gallon of antifreeze (1/2 gallon antifreeze. 1/2 gallon distilled water). The antifreeze that I purchased on-line was Mercedes antifreeze but was a different color (yellowish), but once it mixed it looked the same as the original.
Mike T.
 

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Well, the thermostat change went nicely!!

Many thanks to the folks on this forum Koningster, and mtrevelino for your comments and your references..

Koningster referred me to a GOOD writeup here: HOW TO: Change thermostat - OM648 (W/S211 320CDI) - MBClub UK Forums

Many of the instructions were followed from the writeup, and here are a few of my observations and changes:

1) In the writeup the guy placed a rubber glove over the oil filter hole. I tried that but didn't like the fit so I looked around and found a cup from a happy meal.. The small size empty drink covered the hole perfectly and I folded the excess inward..

2) Like others have said I replaced the antifreeze lost in the change with 1/2 gallon MB anti-freeze, and 1/2 gallon water.. It was easy refilling the unit with everything together. I filled the reservoir and squeezed the upper radiator hose. This seemed to force the air bubbles out of the system and I was able to fill to the top of the reservoir's internal baffling..

The unit has the 3 bolts but the other two that hold the part in place were not pre-tapped holes for me either. No worries as the bolts went with no problems..

It took me around one hour from start to finish..

Now, the car heats up to the proper operating temperature and the mpg on the computer is higher.. Much higher. This definitely works for the better!!

Thanks again for the help everyone!!
 

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I had thermostat changed out from 92C to 92C because of the slow winter warm up and had almost no change in warm up time in the winter. I could drive 15 miles at 55mph before the set point was made. So now I've got a new looking thermostat on the shelf. More aggressive driving would probably help.
I think that part of this has to do with no having a precombustion chamber. That means less surface area for the coolant to be exposed to so less waste heat transferred to coolant.
Winter temps here are 5C and stored in a garage.
 

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I had thermostat changed out from 92C to 92C because of the slow winter warm up and had almost no change in warm up time in the winter. I could drive 15 miles at 55mph before the set point was made. So now I've got a new looking thermostat on the shelf. More aggressive driving would probably help.
I think that part of this has to do with no having a precombustion chamber. That means less surface area for the coolant to be exposed to so less waste heat transferred to coolant.
Winter temps here are 5C and stored in a garage.
Factory is 80C, 92C is what folks change it to to keep the engine running hotter, not quicker to warm up, just hotter, and thereby more efficient and better gas milage and easier on the motor....

You installed it, then removed it and put it on your shelf for future??
 

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Kkaunck is right. It still will take a while for our cars to warm up. I changed my thermostat out because last winter once it reached 80C and I traveled on the interstate, the temperature would drop. I am just hoping that with the new thermostat that it will maintain temperature when it gets cold. Only time will tell. Since I live in Virginia, it really does not get that cold, so taking drastic changes like placing a piece of cardboard in front of the radiator may be a option. Somewhere I read that our cars have some type of louvers in front of the radiator that work automatically (by temperature I assume), but I do not see anything.
Mike T.
 

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Kkaunck is right. It still will take a while for our cars to warm up. I changed my thermostat out because last winter once it reached 80C and I traveled on the interstate, the temperature would drop. I am just hoping that with the new thermostat that it will maintain temperature when it gets cold. Only time will tell. Since I live in Virginia, it really does not get that cold, so taking drastic changes like placing a piece of cardboard in front of the radiator may be a option. Somewhere I read that our cars have some type of louvers in front of the radiator that work automatically (by temperature I assume), but I do not see anything.
Mike T.
The factory thermostat has always been a 90-92C unit but the failure rates seem to be very high as the spring appears to get weak over time and the pressure from the water pump forces water through the unit unchecked..

I tried the cardboard in front of the radiator and it did not work because if you think about it if the thermostat has failed open the water is in a continuous flow and will heat up eventually but probably not to the desired temperature. That made no difference in the temp of the engine..
 

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The factory thermostat has always been a 90-92C unit but the failure rates seem to be very high as the spring appears to get weak over time and the pressure from the water pump forces water through the unit unchecked..

I tried the cardboard in front of the radiator and it did not work because if you think about it if the thermostat has failed open the water is in a continuous flow and will heat up eventually but probably not to the desired temperature. That made no difference in the temp of the engine..

I thought all along that the factory installed was 80 C on the thermostat based on this thread earlier.....So you are saying this is not correct, and it is a failed 92C thermometer that reads 80C? If this is the case, then I will put my new item on the shelf for future too!
 

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When I had the old unit off and the new unit in my hand they had the same numbers on the plunger inside so this leads me to believe the old thermostat was a 90-20 as well..
 

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I have no way to know if the unit I pulled off the car was the original unit or not but it probably was since I purchased the car with 48k on the clock..
 
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