1985 300TDT
Just did a lot of preventive work on my car including new coolant and thermostat. Zerex 05 coolant and Behr 80 degree thermostat were used. My car used to run at a consistent 85 degrees in Florida summers before I serviced the cooling system. It now runs 95 degrees. I know this is the upper end of normal but it just doesnt sit well with me. I would much prefer 10 degrees less or even 5 less. Several posts on different forums say that this is normal for new Behr thermostats....they tend to run a bit higher than their rating when new.
Does the "spring mechanism" {or whatever its called}on the thermostat tend to weaken a little over time and then open closer to the rated 80 degrees?
The car gets no hotter than 95 now, no matter how hot it is outside or how hard I am running....its not overheating.
Is there a different brand of thermostat that opens closer to its rated temperature than the Behr does?
Car has been driven about 300 miles now so I dont think there is an air bubble in the system. Dont they self-burp after a while?
Thanks
John

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1985 300TDT
2013 E350 Bluetec

Wahler.

So the Wahler thermostat is considered more accurate to its rating or is just an alternative brand?

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1985 300TDT
2013 E350 Bluetec

You could still have air in the system, these engines aren't necessarily self bleeding. What I do is turn the heater on full, have the front of the car raised, disconnect the upper radiator hose from the radiator (engine running), fill the engine with a funnel in the raised upper radiator hose. When heat comes out the cabin heater vents, your bled. Is your heater putting out as it should now?
I haven't installed a T-stat for a while but they used to have a small arrow to indicate "which way up" or ahead depending on your housing. It was small and easy to miss. The one I have in my shop has the arrow but I've had it a while so I'm not sure if the arrows are still stamped on the T-stats..
Also its not uncommon for a T-stat to be N/G off the shelf, epically if its not a Wahler as qwerty said.

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

.

system burp.
tight belt
add 1/2 quart of water (since you are in F. you can add even more )

you will hit steady 90 or less

.

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w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered

I ran the car for about 300 miles now...had the heater on a few times and it put out heat fine. I did not fill as you indicated. Also, I didnt install the thermostat. I was changing diff fluid while the MB tech was changing out thermostat and coolant. Cant say if the arrow was pointing up, but the MB tech is very experienced and knowledgable so if it matters that the arrow is up...then I'm sure he did it right.
The car immediately went to 95 degrees and it hasnt varied from that for a week and 300 miles. Its probably not a big deal since the car is technically not overheating but after being used to 85; the 95 kinda makes me notice the temp more.
Maybe I'll just get a Wahler and see if there is a difference> I take it from your comments and Qwerty's that the Wahler is preferred over Behr?

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1985 300TDT
2013 E350 Bluetec

By design, the 617.95 engine is self-bleeding.

Have you had the 617/6 cooling system drained and then refilled and then drive away without doing any bleeding?

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

I believe that I was quite specific in that I was talking about the 617.95 engine. Nothing that I said was intended to apply to any other engine.

If your heater is working OK thats probably in indication its not air. I have never been able to install a T-Stat without bleeding the system (616/7) but it sounds like you had a competent MB guy and you drove 300 miles.
Did you call the MB tech and ask him about it?
Using an infra red temp gun is a good idea to verify the gauge, but nothing should have changed there, but still good to check. If you change it out put the new one in hot water and make sure it opens, check the old one too.

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Sorry, I guess I wasn't very clear with my question. You have drained the cooling system of a 617, filled it with coolant and just driven away? I have not done anything with the cooling system of a turbo 617 so maybe those dont need bleeding?

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Yeah, I called the tech and asked him about it and he said the 95 was normal and dont worry unless it gets above 100. I guess the fact that its only 5 degrees more until a problem is what had me a little concerned. When the car ran at 85...it didnt bother me. He also said, that the new Behr's are opening a little higher than the labeled 80 degrees. {Several posts on this forum confirm that}. I guess my original question was:
Do thermostats "wear out" over time like the one I had in the car? In other words does the opening temperature decrease a little over time just from the multiple opening and closings on the thermostat "valve"?. Does the valve get weaker?
Is the Wahler considered a better and more calibrated thermostat than the Behr?

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1985 300TDT
2013 E350 Bluetec

Well I sure dont feel qualified to argue with a professional MB mechanic but I think 95 is about 5 degrees over what most folks consider normal operating temp.

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

There are two more things you can check. One is the bleed tube between the water pump housing and the block to make sure it's open. Next, try a different sender. I had to try three in my signature car before I found one that was accurate. I set up a portable stove with a pot of water, and immersed a thermostat, the sender, and a mercury thermometer and hooked the sender to the car with jumper wires. I had one sender that was indicating almost 100* just when the thermostat was opening and the thermometer showed the water was about 185*.

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'83 300D, 126K miles.

It cant be the sender because we are comparing the temp before a coolant and thermostat change and after the change. The sender is a non issue. The temp before was 85 and after was higher. Even if the sender/gauge is inaccurate at 85; the temperature was higher after the service.
I took the car for a spin to double check what I am seeing on the gauge. There is a mark at 80 and one at 100 on the gauge so I assume that exactly halfway between is 90 degrees and 3/4 the way is 95 degrees. Looking at it closely; it seems to be probably about 92-93 on the gauge so thats a little better than my initial readings.
I'm nitpicking here and dont mean to imply that anything is wrong with the cooling system. It just seems that the new thermostat is probably beginning to open at a temperature higher than the indicated 80 degrees and is fully opening around 92-93. The old thermostat was fully open at 85 degrees.
Again, no biggy.....just wondering if this is common with a new Behr thermostat and if the Wahler's are more accurately calibrated; therefore better than the Behr's?
I guess the only way to find out is change to a Wahler and see the results.

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1985 300TDT
2013 E350 Bluetec