When I first got my 300D, the temp would stay just above 80 during most conditions, but after a coolant flush and new t-stat, the temps were always slightly higher (90C range). I tried several t-stats from 3 different sources (including MB, which appeared to be the same manf. as Behr) and nothing fixed the issue.

Last week I decided to try a 75C t-stat spec'd for a 116 V8.

The temps have now returned to the 80C range and stayed there throughout my weekend trip to the Central Florida GTG.

The t-stat appears to be very similar in design with the exception of a relief valve? on the outer part.

I'll report back later if anything changes, but I think this has fixed my issue.

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg

I suspect that you caused more of an issue than you resolved. An 80 degree thermostat has a normal operating range of approx 80 - 95 degrees. It doesn't sound like you had an issue with the correct thermostat.

i am always around 90, i think its normal

i removed the A/C rad from infront of the main rad, only the egt's went down 100 degrees for all around driving, water temp is the same

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1985 300D - 599,xxxk - blue interior #265 Monark Nozzle, AL129X, 15" Ronals, Gen II Big Brakes hunting
1985 300D - 491,xxxk - in prog-{A-A IC, 3" exhaust, psi\pyro, 28*BTDC, Hella Euros, IP Limiter removal
1985 300TD - 783,xxxk - parts car,used new engine with ALDA cap inplace
1987 Kenworth T-600 8LL 425 CAT Mech. - 6,000,000+k - DEI exhaust wrap, punched through resonators, 1 recent rebuild,

what issue have I caused?

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg

You installed a thermostat that will cause your engine to operate at a temperature lower than specified. It may seem logical that cooler is better; it isn't necessarily that way.

is how many years and/or miles has your radiator been in use?

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1987 300D (230,000 mi on a #14 head-watching the temp gauge and keeping the ghost in the machine)
Raleigh NC - Home of deep fried sushi!

unknown. I don't have any records that indicated a replacement, but most of my service records are for the routine stuff not repairs.

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg

when I say coolant flush, I mean a coolant exchange with a water rinse. I didn't do a citric acid flush or use any other chemicals. it had the green stuff when I got it.

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg

I think the only issue that you caused was more work for yourself than needed. Operating temp of 90C is pretty normal. Anything between 80-90C is pretty normal when you start operating much below or above that you have issues. My wagon runs a 90 all day long, while my 240 is closer to 80.

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I've installed a t-stat that makes my car operate at the same temperature it did prior to switching it from an older Walher to a modern Behr.

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg

When you buy new tires, do you make sure they match the tread depth of the old ones?

when you comment on posts, do you try to be a jerk?

if you were to poll w123 owners here, I'd bet you'd find many who see operating temperatures just north of 80C, which is where mine was at before I changed thermostats.

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg