Hello Pelican Parts people I'm here yet again with another question. I recently changed out the thermostat in my 1984 300 diesel because the temperature gauge on the car was never getting up to 80 degrees and if it did it would take forever. None the less I decided it was time to get a new thermostat oh, so what I did was ordered a OEM Mercedes Benz thermostat. I installed it on the car and did a full coolant flush G 05 coolant it's what was recommended on The Forum. I noticed after I installed it and took like what felt was a 10-minute Drive the car temperature rose up to 80 instantly then gradually made its way to 85 which is a nice thing because it provides a hot toasty Heat especially in the winter time in Northern Virginia. Sometimes it would make its way to 90 but other than that it would just stay at 90 and won't go higher.


I know I install the thermostat correctly because the O-ring was pre-installed on the thermostat and it could only go one way in the housing. I ordered the part from Pelican parts website and it says they start to open up at 80 degrees. Are these normal operating temperatures? Should I be worried?

I have bought thermostats that had the temp on the box different from the temp that was actually on the thermostat itself.

If you suspend the thermostat above the bottom of a pot and heat the water (put some salt in it so it wont bubble as much) up and measure the water them temp (keep the thermometer off of the bottom of the pot) and watch when the thermostat opens and is full open and you will get an idea as to if you higher temp is being caused buy the thermostat itself.

On American cars I have seen and had coolant flushes loosen stuff that ended up plugging some radiator cores and leading to a higher coolant heat.

Had an incident where the temp censor had so much crud on it the crud acted as an insulation keeping the temp sensor from working as it should. In my case I pulled it and cleaned it manually but a flush could also clean off a temp sensor and get it to read correctly.

Concerning the 95 degrees C as long as it stays there in with your engine under any and all loads and ambient temps it is actually within a normal range. My 84 300D has a read line on the gauge at 100 degrees C so I am assuming that is the high end of the normal temp range.

To cloud the issue is that if the oil cooler thermostat inside of the Oil filter housing is not working one would think that would also raise the coolant temp.

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84 300D, 82 Volvo 244Gl Diesel

175F is normal around there.

For what it's worth, replacing the thermostat, flushing the system/refilling with g05 and fixing the odd electrical tick on the gauge were tremendously helpful, but it wasn't until I removed the radiator and sprayed it thoroughly with simple green and a garden hose did I achieve consistent running temps (80-82). It *looked* clean. It wasn't.

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1981 240D 4sp manual. Ivory White.

also depends where you live.Here in southern mountains,ran a cooler 70c stat,82c was the highest I saw it.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

My SDL never goes above 80*C, but my E300 runs hotter.

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1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.

Greetings from the county up north. I grew up in NOVA.

My daily 300D 84' stays fixed at just under the 80°C mark most of the year. Around this time of year and the colder periods it stays around the 60°C mark. I use cardboard to block off the oil cooler and part of the radiator, but it doesn't help much, just gets it warmer quicker in the mornings.

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Onus probandi incumbit ei qui dicit, non ei qui negat

I recondition w123/w126/w124/w140/r107/r129/ steering boxes!


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]

All of my benzes have tended to run around 82c except when climbing or running at higher speeds.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

"Normal" should be between 80 and 90 degrees C depending on the ambient air temperatures I see here in Northern Europe (-10 to +30ish)

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

78-80c is operating temperature. 85c+ is usually 95F+ outside with the A/C on.


It sounds like there may be some deposit build up inside the radiator. Anytime I have had a Benz over 80c the radiator had calcium build up inside. Sometimes you can see it through the upper/lower radiator hose port if you shine a flashlight into there.

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Nosce Te Ipsum "Know thyself"

It's tough to make that argument when the OM617 thermostat only begins to actuate at 80ºC and does not fully actuate until 94ºC.

Have you been putting milk in your cooling system?

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

This is based on the five w116 I have owned four 300SD and one 450SEL. When they have ran hotter than 80, they need their radiators completely cleaned out, and re sealed. They have also all had green coolant prior.



Calcium < lime scale/rust wrong term.

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Nosce Te Ipsum "Know thyself"

When I first bought mine (83 300D), it had green coolant and slooooowly crept up to ~70C (stuck thermostat).


I replaced the thermostat with an 85C unit and switched to G05 (no citrus flush, just a hose). Mine now sits around 88-94C fully warmed up. Never breaks 99C, even when going up big steep hills @75mph for ~5min.


Probably shouldve gone with an 80C thermostat... and my secondary fan doesnt work, and my fan clutch is likely getting long in the tooth, and the radiator likely has sediment/build up... and yeah, its warmer than I'd like, but I'm not worried by those temps either.


(and these temps are from the instrument gauge, which could be inaccurate ... good idea to verify the temps... I just need to follow my own advice.)


I'd say if it ever breaks 100C, keep an eye on it. If you get consistent temps at ~100C, prepare to work on it. If it breaks 110C, pull it over or get home ASAP. Approaching 120C? You should already be pulled over and ready to turn it off.

80C from Wahler is OEM on OM617.

Mutt (modified OM617) peaks at about 210F at the finish line but cools right back to 180ish on the return road. Never any trouble with that.


Dan