Good evening,
Car is showing odd behavior:

Top coolant hose, coolant hoses to and from grease tank are hot(this cuts into the coolant system on the engine side of the thermostat, splicing off the hose/metal tube towards the heater).
Bottom coolant hose is not. Engine side of thermostat housing is hot, radiator side is not (leading me to believe it is not stuck open causing the overcooling).

I am really unsure of what is going on here.
I swapped thermostats with a known good one and same thing. Thermostat I took out was at full open in boiling water in my home.
Dash board, factory temp gauge never makes it to 80C.

Thank you for all your help.

My initial guess is that lots of heat is going into your grease tank.

As I was typing that it occurred to me that the gauge could also be bad. Have you verified temperature with an IR thermometer? If you don't have one, get one, they aren't expensive and have about a million uses.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

If this was not a Car with a modified Coolant system I My wild guess would be the Fan Clutch not disengaging and the Fan is turning all of the time; if it has a Fan Clutch.

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84 300D, 82 Volvo 244Gl Diesel

I would confirm accuracy of dash gauge first. Is this a new behavior?

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

no fan clutch on a 240 from factory.

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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.

Most of the radiator is cold, the top remains hot.

The temp gauge is working properly, but never moves (showing no open of the thermostat, never reaching temperature).



We flushed the coolant system, very clean, no sediment came out and the flow was very strong.



I then ran the car without the thermostat in. We found the water shot out once we touched the gas, I would say the water pump is still working, there was no leaking before this.



I also verified correct thermostat installation and boiled it to make sure it openned and closed properly.



I will be putting everything all together tomorrow and running the car.



So odd that it would be overcooling.

I'm having the same issue with a 73 220D.
I changed my thermostat last night with a genuine MBZ one and flushed the system and added fresh coolant. My temp gauge still only goes up to the 150F mark but I need to check its accuracy. Also my heat is only blazing hot when I'm driving and while accelerating the car, at idle and slow speeds the heater is cold.

Good point, I did a full flush/fill with CarQuest's $2.19 flush. I am back to happy temps.

I am very unsure of what the original issue was, no real sediment came out of the coolant system at any time.

I drove all day on free fuel.

Thanks