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1983 380SL / 101K Miles
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160 Posts
Discussion Starter #1 (Edited)
I hope that this isnt the stupidest question ever posed, but here it is. Ive been told that my thermostat is broken and needs to be replaced. My question is this. If its broken then why does the temperature gauge on my dashboard seemingly work fine. Are these completely unrelated items? Is there something else in the engine that controls that dash console reading?
Thanks for bearing with me....

Also, which one do I need? a 75c or the 84c?
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
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7,150 Posts
I hope that this isnt the stupidest question ever posed, but here it is. Ive been told that my thermostat is broken and needs to be replaced. My question is this. If its broken then why does the temperature gauge on my dashboard seemingly work fine. Are these completely unrelated items? Is there something else in the engine that controls that dash console reading?
Thanks for bearing with me....
Why were you told the stat is broken? Does the car not get up to running temp? Does it overheat?

We need a bit more info, I think.

...and the stat is independent of the gauge in the dash. The dash gauge uses a different "sensor" to monitor the temp of the coolant flowing thru the engine.

Edit: 84C is correct for your car, if I recall correctly. In Portland, I'd expect 84 would be much more appropriate than 75
 

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1983 380SL / 101K Miles
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160 Posts
Discussion Starter #3
My mechanic mentioned it today, and hinted that I may as well replace it myself and save myself some money. But I am confused as to why they are available in 2 different temperatures? I'm pretty sure its supposed to 84c, but just wanted to be sure.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
Joined
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7,150 Posts
My mechanic mentioned it today, and hinted that I may as well replace it myself and save myself some money. But I am confused as to why they are available in 2 different temperatures? I'm pretty sure its supposed to 84c, but just wanted to be sure.
Do you know what symptom led him to recommend the replacement. It is no big deal, anyways, but changing one can be difficult for some less mechanically inclined. Air must be fully burped from the system. Also, changing the stat can cause users to believe their car is suddenly overheating... Seems older stats seem to never close fully, and the car runs cooler, but when a new one is fitted, the car appears to heat up a bit more, worrying owners needlessly.

When you hear someone telling of their SL never running above 85-90C, I can bet the stat is FUBAR, and not closing fully...
 

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Always Remembered RIP
1979 280sl 4 sp w/ac 1957 MGA 1998 volvo xc/70 2004 F150
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6,050 Posts
EARS, I think Drex was having problems with his WUR so an operating stat is a must to hunt down warm-up problems.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
Joined
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7,150 Posts
EARS, I think Drex was having problems with his WUR so an operating stat is a must to hunt down warm-up problems.
Got'cha... stuck open, car not reaching operating temp in appropriate time (or ever). That'd do it...
 

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Registered
1983 380SL / 101K Miles
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160 Posts
Discussion Starter #7
Got'cha... stuck open, car not reaching operating temp in appropriate time (or ever). That'd do it...
Yeah, that sounds along the lines of what he said. SO, whats the right one to get (temperature wise?)

Also, is there more to installing it than dropping it into place?

PS. WUR is functioning 100% (thank christ)
 

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1987 Mercedes-Benz 560 SL
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973 Posts
...why they are available in 2 different temperatures?
Generally speaking, cars driven in extremely cold climates use a higher temperature thermostat to ensure the heater blows hot, rather than just warm, air. Five Celsius degrees (9 degrees F) might not make much difference to the engine (assuming the cooling system is otherwise sound), but the heater core will operate more efficiently in sub-zero driving conditions with warmer antifreeze flowing through it.

When I lived in Germany I opted for a 92C thermostat in my Volvo 244 rather than the stock 87C. Even though the antifreeze was only 5 degrees C hotter when the car warmed up, the change was noticeable and really did make car much more comfortable in winter. I can't say that the engine warmed up any faster, but the cabin reached its comfort level more quickly than with the cooler 'stat.

There may be other reasons to vary thermostat operating temperatures, but that's the most compelling one I've experienced.

Good road,
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
Joined
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7,150 Posts
^^^

I agree, and as I -posted earlier above, 84C would be my recommendation, given your location.

Also, as posted above, upon installation, bleeding the system is paramount! Instructions are in the manual.
 

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1987 560sl
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36 Posts
Replacing The Thermostat In A 560SL

A few weeks ago, I noted that my coolant temperature was running around 65 degrees C. I replaced with a new stat and the temp is now running between 85 and 90. Fuel economy improved with the change. Attached is a pdf with photos of the procedure I used.
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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29,166 Posts
Some would say to test the new thermostat in a pot of hot water to, at least, check the function.


I've yet to do that in 33 years of dicking around with cars.....and have yet to be disappointed.
 

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Registered
1988 560SL (California Model)
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5,074 Posts
If you DIY just remember the thermostat is on the passenger side of the housing...not the top at least on the 560SL. I would like to think that I am not the only one to make a "Chevy" mistake...
 

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Registered
1983 380SL / 101K Miles
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160 Posts
Discussion Starter #15

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
Joined
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7,150 Posts
OK, time to buy one. There are a few on ebay but this one sounded best (I wrote to the guy and he said its made in Germany)
If your dealer is close, buy from him. Real reasonable when I bought mine. BEHR is the preferred, I recall.
 

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Registered
1983 380SL / 101K Miles
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160 Posts
Discussion Starter #17
If your dealer is close, buy from him. Real reasonable when I bought mine. BEHR is the preferred, I recall.
Ive never dealt with the dealer here, as in my past experiences Ive found that buying from them is usually the most expensive option. I HAVE dealt with the Benz Classic Center in California, and he gives me a 15% discount. Maybe I'll get in touch with him first..
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
Joined
·
7,150 Posts
Ive never dealt with the dealer here, as in my past experiences Ive found that buying from them is usually the most expensive option. I HAVE dealt with the Benz Classic Center in California, and he gives me a 15% discount. Maybe I'll get in touch with him first..
Its been a coupla years since I bought mine, but I don't remember it being as much as the ones advertised on ebay. In fact, I recall getting change back from a $20 (but not much).
 

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560 SL
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52 Posts
Engine temperature

Do you know what symptom led him to recommend the replacement. It is no big deal, anyways, but changing one can be difficult for some less mechanically inclined. Air must be fully burped from the system. Also, changing the stat can cause users to believe their car is suddenly overheating... Seems older stats seem to never close fully, and the car runs cooler, but when a new one is fitted, the car appears to heat up a bit more, worrying owners needlessly.

When you hear someone telling of their SL never running above 85-90C, I can bet the stat is FUBAR, and not closing fully...
I thought a cooler running engine was a good thing? My temperature seems never to run above 85-90C that you mentioned, and that included during the smoking hot (and humid) Florida summer. The temp gauge was always within the stated range (after a warmup period) and actually led me to wonder whether it was broken (as I had just purchased my first MB last May).
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
Joined
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29,166 Posts
I thought a cooler running engine was a good thing?
Engines are designed to run at a specific temperature (+ or -).
They are tuned and will be the most efficient at that temp.



Example:

My SL was running 10C cooler than designed thus my idle was always at 1200 to 1400 rpm.

Basically stuck in "warm up" mode.


And yes, it was a bad thermostat.
 
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