Hi folks,

First post here! I have been a long time lurker and always been a fan of the W123.

I ended up buying a 1982 300D middle last year for $1500. As you might have guessed, it needs some work. I had 1 engine mount and guibo joints fixed at a shop and fixed a bunch of interior stuff before putting it away for the winter.

I had noticed that the car never got up to operating temps.
Even in the peak of summer, it would creep up to 80C on the dash in slow stop & go traffic. Running on open roads would cause it the engine temp to dop down to about 60C.

If I turned on the heater, it would drop very quickly (in about 30 seconds) to just over 45C.

I have verified the gauge reading with an IR thermometer. The numbers check out.

The PO filled it with Peak green coolant and distilled water (for a 50:50 mix).

Yesterday when the temps were in lower 40s, the gauge never went over 50-60C.

So going back to the issue of my car never reaching operating temp, what could be the problem?

1. The radiator cap is a Stant with 13psi rating. I am thinking of replacing it with one from the dealer that is rated for 120kPa. Can a faulty radiator cap not let the car warm up to operating temps & display the symptoms I am describing above?
2. If this does not fix it, then I am thinking of replacing the thermostat (the upper & lower hoses while I am at it) and refilling with Zerex G-05. If I end up at this step, then I will get the Behr/Hella thermostat that's been recommended on older threads in this forum. Are there any tips/tricks to burping the cooling system? Most probably I might have to do this with the car on level ground.
3. I have not checked the monovalve since I get momentary heat prior to the temp gauge falling down to 45C.

Am I on the right track? Sorry for the long post.
Help and advice would be appreciated in fixing this problem.

Welcome to the forum.

The low operating temps, points towards the Thermostat.

When we first got the 85 300D back in 97. I was taking it to a shop till I fully understood how everything worked.
They noticed the temp not getting to 80C or 176F. The Stat was broken, a spot weld on a piece came loose.

Get a Bher Stat and you will be good.
Be careful with the 3 small bolts holding the Thermostat Housing together.
They have been known to break, steel bolt into aluminum = rust and corrosion.

To burp the system, elevate the front end, remove the upper hose at the engine and fill till it won`t take any more.

Lets hope the shop did not use EURO parts. There is a long thread here about EURO parts.


Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

Euro parts are OK....the entire car was originally made with Euro parts. I think you mean URO parts.

__________________
Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Thanks. According to the shop, they used OEM make for the engine mount (passenger side) and the guibo joints. Also had to get cracked flex pipe fixed - turning on the air would suck in all the exhaust smoke .

I read enough bad things about URO prior to me buying the car - so I am wary of having it on my car.

I will go ahead and order a new t-stat with hoses. What is the correct rating for the radiator cap? Is 13psi too low? Or can I just leave the one in?
The dealership said they sell 120 kPa caps - which is roughly 17psi.
Researching online says that the car came with 100kPa caps (14psi) which I cannot find anywhere.

OOPS!!! You got me on that one. What was I thinking?

URO parts...stay away from them.



Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

Has anyone used a spill free funnel (Lisle) to burp the cooling system?

I think of using it as an alternative to getting ramps. I live in flat land and it is hard to get a steep slope where I can park the car nose up as suggested in older threads.