i have been trying to help my friend who's 1984 300td has been running hot for years. it doesn't seem to run any hotter or cooler on the highway or stuck in traffic. just 95-105c and sometimes will slowly heat up or cool down it that range. so far i have:

-replaced thermostat 4 times with both new MB 80c stats and known good used ones.

-did a citric acid flush and it didn't come out too awful. (see pic)

-new water pump

-tried another temp sender and known good gauge cluster section

-checked engine ground and cluster ground along with cleaning all connections that go to the temp sender

-installed the 9 blade plastic fan with new behr clutch. moves plenty of air.

-has a month old new nissens radiator

I'm just stumped, guys! is there anything you can think of that could be left? i haven't checked the metal coolant bypass line to see if clogged but the rest of the cooling system has been well maintained. the wagon shows 278k and runs great with little blow by. the timing chain was recently been replaced but it has run hot for years. maybe ip timing retarded adding heat? probably not. i also didn't notice any abnormal pressure like a blown hg. any suggestions appreciated!

Attached Thumbnails

 

__________________
83 300CD- sanden, dual p/f condensers, 160a alternator, ect
91 300TD- 722.6, #22 head, 3.5L IP, w140 manifolds, ect

is thermostat in correctly?not upside down?Do you have a lower hose collapsing?Has air been purged from system?

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran

I went through similar problems with my old 123 years ago and replaced exactly what you have, I was not quite that hot but at 88 degrees. At the time I had tested 4 new thermostats over a period of a couple of years my conclusion was a different wax was used inside the thermostats which caused the increase in temperature. My solution to correct this over temperature was to drill a 1/8 inch hole through the thermostat. All was fine in the summer months it ran at 81 degrees. In winter however it would not get up much past 70 degrees so I'd switch thermostats summer winter. I don't think you'd have to switch living way south. That's a real head scratcher or was for me at the time and can't say I liked the solution but it gave me peace of mind.

Mine's been running at 100 for about eight years. It's not a problem.

__________________
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.

I think the thermostat is still in question. I had 3 toasty ones in a row for my car and decided to cut some of the internal spring and my gauge now shows exactly 80c. I got stuck in traffic on a test drive and it stayed at 105c with ac on and didn't move much once rolling. If it was going to overheat, it would have there.

__________________
83 300CD- sanden, dual p/f condensers, 160a alternator, ect
91 300TD- 722.6, #22 head, 3.5L IP, w140 manifolds, ect

Yes it's in correctly and good new hoses too. It will stay at 100c or so when idling so I checked. And yes on air being purged

__________________
83 300CD- sanden, dual p/f condensers, 160a alternator, ect
91 300TD- 722.6, #22 head, 3.5L IP, w140 manifolds, ect

80-100C is the normal operating range of the MB diesel.
with a/c on, and traffic, it should hit 100, but not go over.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

have you verified the temp with an IR thermometer?

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Actually at that milage I would include a injection pump timing check. More heat might be developed with late timing. I would check the chain as well for excess stretch. I wonder what kind of fuel milage that car is delivering.

Also a thermal check for cold spots in the rad when it is at temperature as well. Especially if turning the heater on drops the temperature.


Actually with a cast iron head and block the temperature it is running at is not a major issue. .My kind of rule is if it never boils over I seldom would get really concerned. If you have a fluid coupled fan makes sure it passes a simple test. Cast iron heads are far more tolerant of running a little hotter. I was sorry to see them go out of production on most cars.

Yes but where is the best place to get a reading?

__________________
83 300CD- sanden, dual p/f condensers, 160a alternator, ect
91 300TD- 722.6, #22 head, 3.5L IP, w140 manifolds, ect

If the transmission fluid is overfilled and burning....it will cause the transmission to over heat and thus the temp of the car to rise.

If the thermostat in the oil filter housing isn't opening and allowing hot oil to flow into the oil cooler at the correct temp will also cause the engine to be hotter then normal..

__________________

will check atf next time i see car. and the oil cooler thermostat seems to be working well. thank you!

__________________
83 300CD- sanden, dual p/f condensers, 160a alternator, ect
91 300TD- 722.6, #22 head, 3.5L IP, w140 manifolds, ect

I disagree. I've had a few of these and when driving up a hill with A/C on it should go up to 95 max and then go down to about 90 when flat driving is resumed. Most W123s are neglected and have a long list of repairs needed. That doesn't mean that is how it's supposed to be.

The first thing is to determine definitively if the temperature is correct as neglecting it could cause some much more expensive problems down the line.

Dkr.

Point it at the thermostat housing and all over the top of the radiator. Shoot the upper radiator hose and the lower radiator hose. By doing this a few times, you should eventually get a story about the temperature.

Dkr.

Doesn't it take about 15 miles of driving for this to open up?

Dkr.