The 240 engine is going to produce ALOT less heat soak than a turbo 5cyl. The turbos really don't have a much bigger radiator. That is probably why the 240 will run ok without.

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.

so i guess that proves that the factory was wrong to provide an elaborate method of controlling the coolant flow, right?

people smoke like fiends and drink a quart of gin and live to be a hundred too i hear.

that doesnt make me want to do either that or run without a stat.

maybe his houston experience proves that the bypass stat is more of a warmup thing than a max cooling device. but note too that he is not running ac which is a major cooling load.

but the factory manual definately recommend against running without one.

but hey it is your car.

i guess maybe you think running at the recommended oil temperature is silly too.

tom w

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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.

I didn't draw any conclusions. I simply asked you to read the thread and comment again.

So, what do you do? You draw conclusions on what I'm thinking. Very clairvoyant of you.

I've seen quite a bit of anecdotal evidence that suggests that folks can successfully run without a thermostat. This might point to the fact that the factory is incorrect.

Diesel Giant has had success by drilling the thermostat to allow more flow.

Dr. Bert has not run a thermostat on the 617 in years.

However, Roy has run without a thermostat and the 617 overheated for him.

Have you run a 617 without a thermostat??.........or are you simply reading the manual for us?? If it's the latter..........and I suspect that it is..........consider this a thanks for the invaluable info.

I guess. How would I know?

At this stage, I don't know what it is.

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-- 1983 300D, acquired 10/19/2005 at 215,000+ turbodiesel miles ... engine croaked almost immediately ... back on the road at 217,210 with a 144K turbo motor from a donor '85. ... May 2007, replaced radiator. ... Now (2/28/08) about 240K miles and dead due to battery?

Just because the water temp shows operating temp does not mean that it's even.

I tried running no t-stat in on old chevy 350 powered p/u last summer. I measured the cyl head temps with an infared thermometer.

The water temp gauge showed 160. The infared agreed, with the front of the engine. The heads at #4&8 read 300*f.

READ IN THE LAST PICTURE AS PER FSM: "At coolant temps above 94*c, the bypass line (C) is closed by the bypass disc. The entire volume of coolant should flow through the radiator. ... IT IS THEREFORE WRONG TO REMOVE THE THERMOSTAT FOR BETTER COOLING OF ENGINE."

If you want the engine to run cooler than 82*c, what you need is a cooler rated t-stat.

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Remove the radiator.
Take it to any average radiator shop for a FLOW test.
They will be able to tell you what percent, zero to ninety nine, of flow is lost..

After recently fixing my 85 300DT following a front end crash,I bought a used radiator that looked like new,but the car ran hot 100-105. I actually bought a 75 degree C tstat from an older 450 thinking the temp would come down. Am I incorrect in thinking a 75,80 ,or 85 woluld make a difference. I thought the car came with a 85 degree C tstat.or is that determined by location? While reading more threads and waiting for the new tstat i tried the garden hose on the fins(not even the pressure washer). About two pounds of sand was on the driveway when i was done.The car ran at normal temp but developed 2 or 3 pin hole leaks. These leaks have sealed up over a few days.It seens bad radiators seal themselves up with their own crud/sand.I'm saving for a new radiator but what tstat is correct for trips from nj to canada to florida? thanks

if i have misunderstood your intent here, i apologize.

tom w

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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.

english is not my best subject. i guess i misunderstood your intent here too. i apologize again.

tom w

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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.

No problem.

I'm just not taking the manual at face value on this one. I fully understand the flow issues when no thermostat is used and, it may well be the fact that you cannot run without a thermostat under heavy loads.

If the engine loading is kept to fairly moderate levels (no hills), the loss of coolant to the bypass may not be a significant factor and would explain how those fellows run without one. And, the thought that the 616 can't produce enough heat to harm itself is probably a valid point.

I'm certainly not advocating running without a thermostat.........just trying to get a handle on the success or failure of those folks who have done so.

Geez, I don't have time for this. I'm working six 12- to 18-hour days a week, only off on Sundays.

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-- 1983 300D, acquired 10/19/2005 at 215,000+ turbodiesel miles ... engine croaked almost immediately ... back on the road at 217,210 with a 144K turbo motor from a donor '85. ... May 2007, replaced radiator. ... Now (2/28/08) about 240K miles and dead due to battery?

A follow up on my post No.7, want to make it clear that I DO NOT at all recommend the removal of a functional thermostat, if it is not broke do not mess with it, but in my case I was faced with number of thermostats that remained shut after several hours of driving, the mechanic experimented with three different thermostats, all three refused to open up under normal driving conditions, so the choice was clear, I was forced to remove the thermostat. This all happened while I was in Washington State and the local MB shop that worked on my car was specialized in older MB’s like mine, they were doing cooling system service work including installation of a new radiator, flushing the system, hoses etc. A few months later I drove back to Houston, about 2300 miles, no cooling problems. While stationed in Washington State I did considerable weekend driving in the Cascades, lots of mountain passes etc, no cooling problems.

Houston based MB dealer has only one type thermostat for this car, if there are lower temp. thermostats available from another source, I would like to try them on my car, if you all give me name/contact information.

The fact that it was even suggested to drill holes around the thermostat to make it work, is a clear indication of MB design screw up with this particular item on 240D engines.

Vahe
240D 77/350K

We kind of hijacked your thread........sorry.

The first line of attack must be the radiator. You can remove the thermostat.........or change the thermostat........but..........in most cases.........it's not the problem.

The radiator fails in two ways:

1) It accumulates quite a bit of debris between the fins and restricts the airflow. To remove same, you must remove the radiator from the vehicle and thorougly clean between the fins with water pressure from a pressure washer or compressed air in conjunction with a suitable condenser cleaner. It's very difficult to get the debris out of those fins. Hold the radiator up to the sun and peer through it. You'll see what I'm referring to.

2) If the cooling system was not maintained properly, the internal passages of the radiator are clogged with corrosion and the radiator won't accept the coolant that the engine is sending it's way. The solution here is a citric acid flush, a long and time consuming procedure, with no guarantee of success.


If you have no time for any of the above, you'll need to purchase and install a new radiator. The cost is about $300. and it's a 90% bet that it will solve your problems, especially if the radiator is original.

Not wanting to hijack the thread again but it is of particular interest to me as I've been noticing my 81 240D simply doesn't get hot. I assume the TStat is failed open as it takes quite a long time to reach operating temperature - in Phoenix. Once it does. Despite the fact that the temperature has been over 110 for tha last couple of months the temperature needle has never left the 8 on the 80 degree mark. It's come close a few times idling in traffic but there's never been a situation where there was ever even a sliver of black between the needle and the number. Guess I'm lucky the 616 doesnt generate enough heat to cause problems with a malfunctioning TStat. I was going to replace it but now I'm not so sure.

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

Replace it.
Your engine is not reaching correct operating temperature = carbon build up in the cylinders.