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78' 300D
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Discussion Starter #1
I have a 1978 300D and it was roughly 100f earlier today in Socal. My car was run quite hot. Just wondering if that is normal for these older merc's to run pretty hot on days like this or if there is something wrong with my coolant system. I still have to do a coolant flush and change the stat on it but i have no leaks as far i know of.

What i do notice is that i am driving uphill the temp goes up and when i continue to drive on level or downhill highways the temp stabilizes. I think this highest it got today was right above the last knotch above the 175 mark on the gauge. Just want to hear your thoughts, thanks.

Andy
 

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1979 280CE
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6,118 Posts
the mark above 175(80C) is 212(100C). You don't want the car to run much past 212(100C) but thats OK on a day where its 100F outside.

In traffic after a long time the temp will rise to 212 but when driving its about 190(approx. 85-90C).
 

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Mine got up to 90C yesterday. It was HOT out (san diego); and the blower motor wasn't working...

oh, and I have recently flushed the coolant, no leaks, etc.
 

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1981 Mercedes 300D
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1,249 Posts
The hottest I've ever seen mine go was around 90*c, and that was the last time I drove my car through the Grapevine in CA (summer 2004). I was reaming on it going uphill, w/ the AC on.

Despite being a non-turbo, the car took it like a champ and managed to stay at a speed fast enough to keep up with left lane traffic. It was rather noisy having the engine wound up so high though. :D
 

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EURO 280CE
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my euro runs hot, it likes 95-85c.
today for the first time i stopped for snacks and turning it back on noticed it was over 100c.

im really scared when it gets into the 90's here the car will get too hot
 

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78' 300D
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54 Posts
Discussion Starter #8 (Edited)
mine was running a little over 100c just right now through the inland empire. my computer says its about 99-100f outside but it always seems much hotter dispite what the experts say. plus the freeways have a lot of inclines, could that be a contributing factor?

also will conducting a coolant flush and changing the stat on it help it run significantly low in temp? I read on dieselgiant to drill holes in the stat to keep the temp down in hot climates. or is there a "low temp" stat i can purchase somewhere?
 

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1984 300CD, 1983 240TD Euro
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2,650 Posts
I run from San Bernardino to Palm Desert W/AC and my gauge splits the upper 0 on the 80.
 

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1984 €uro 300D NA
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758 Posts
With a stock 80*C (176*F) t-stat I always see 82*C once fully warm. However I also have an accurate aftermarket water gauge in *F installed. Usually I see 190*F once fully warm but today I saw 195*F for a brief while then it dropped back down to 190*F. Ambient temp 93*F. Why a 80*C (176*F) t-stat runs at 190*F 98% of the time still baffles me but I'm good with a 190*F norm.
 

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1983 W123 300CD OM617: 1992 W124 400E M119
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235 Posts
mine was running a little over 100c just right now through the inland empire. my computer says its about 99-100f outside but it always seems much hotter dispite what the experts say. plus the freeways have a lot of inclines, could that be a contributing factor?

also will conducting a coolant flush and changing the stat on it help it run significantly low in temp? I read on dieselgiant to drill holes in the stat to keep the temp down in hot climates. or is there a "low temp" stat i can purchase somewhere?
If you're not stuck in traffic you probably shouldn't be running at a bit over 100C. That seems a little hot to me - it's not at :eek::eek: stage, but I'd investigate. My CD only gets over 100C if I'm idling in traffic w/ the A/C on.

The T-stats in these cars almost always fail in the open position - not sure I've ever seen one fail shut, which is a good thing. DON'T drill holes in your T-stat. That will NOT do any good. If you have a run-hot problem, fix the problem. There are only a few things that it can be.

1. When was the last time you did a citric acid flush? Do this first. It takes some time to do and is a bit messy but you will be :eek::eek: at what comes out of the system. That will probably make a huge difference. Change the T-stat while you are at it, and use the proper coolant and distilled water.

2. Is your radiator original? If it is and the citric flush doesn't reduce your temps, replace the radiator. Very easy job and inexpensive, the originals are generally so choked up with road debris that they ought to be replaced.

If you've still got a hot problem after these two steps (you likely won't) then you may need a new fan clutch or water pump or both. The good news is that the cooling systems are very simple, parts are inexpensive, and all of the parts are very easy to replace - fan clutch is a little tricky but not too bad.

Report back.
 

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money pits of various forms
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Once you hit 100C bad things are likely to start happening.
 

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1983 Mercedes 300DT 301500 miles
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191 Posts
With a stock 80*C (176*F) t-stat I always see 82*C once fully warm. However I also have an accurate aftermarket water gauge in *F installed. Usually I see 190*F once fully warm but today I saw 195*F for a brief while then it dropped back down to 190*F. Ambient temp 93*F. Why a 80*C (176*F) t-stat runs at 190*F 98% of the time still baffles me but I'm good with a 190*F norm.
Same here 80C t-stat and when fully warmed runs at 82-83C (according to gauge in dash). I've been up to 97-98C on a 100F day and a 6-7% incline and the car floored and doing 80MPH so I can't really complain :)
When it idles it stays at 82-83C. I would assume that maintaining the temperature at idle (if the t-stat is good) would mostly depend on the clutch fan.
 

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81' 300SD, 82' 300D
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Mine hovers around 85-95*c. Today was a nice hot day too, we reached 90*F down here.

3,000th post, yay me! lol.
 

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Typically runs midway between the 175F and 212F marks. Recently, it will randomly run hotter, changing temp frequently and running up to 212F in traffic. Ambient is usually in the 80s, getting hotter.

Previous owner told me: "don't run A/C in the summer, it'll overheat." Currently, A/C and blower fan don't work. I will do a full cooling system flush within two weeks.
 
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