I am sure this has been discussed but I am having trouble finding a situation close to mine in the forums here, so excuse me if I missed a thread just be kind and shoot me a link.

On my 87' 300TD the car's temp gauge I have read should never reach 100 degree's C. Now that it has been getting hot and I have been using the A/C I want to know if this is a sign that something needs to be done. The car is not over heating.

With the A/C on and on the highway the car is just a hair above 80 degree's C. When I come to a stop at a light it gradually goes to just under 100 degree's C. It has never gotten to 100 degree's and if I ever see it there I have been told to pull over and shut the car off immediately (sound sain?).

Anyway its not like just a hair above 80, I come to a stop, and it SHOOTS up to 100; it is gradual but I am wondering if that means I need to replace the fan clutch, or that I should look into something else.

You guys are very knowledgeable and I trust your opinions, I want to keep this car COOL, and I was thinking about getting a small intercooler fabricated onto the car just for a piece of mind but that is a whole other thread.

Let me know what you guys think, is it normal or should I start looking into things?

Thanks for looking!,

Franksta

__________________
'87 300TD Estate (Panzer Wagon, Sold)
'95 E320 Estate (Sabertooth, Sold)
'94 E500 (Stark 1, For Sale)
'04 VW GTI (Rhino, Sold)
'12 VW GTI Autobahn (Shadow)

A couple of possibilities. First, my 602 and 603 cars do hit 100C idling with the A/C on occasionally, the viscous fan clutch doesn't engage until around 100C, check the FSM, I believe it is around 96C? The electric fan should be running on low with the A/C compressor running, have you verified this? If not, a very common problem is the speed resistor behind the L headlamp, cracks and fails (ceramic), fairly cheap. Next is the high-speed of the same electric fan, I'm not sure the temperature that's supposed to turn it on, I believe it's 105C but again you might want to check.

Last, the temp gauge is a voltmeter, if the battery is weak, it might not maintain 12v at idle with the blowers and stuff running, turn the headlamps on/off to see if it moves the needle. The '87 124 charging system doesn't put much out at idle and you're running partially from the battery if you're idling with much electrical equipment on. Check the grounds also.

Last, 100C isn't bad for the engine if it's full of circulating, pressurized coolant. If the coolant isn't pressurized, it's boiling in the head, if it isn't circulating or not full, there can be large temperature variations in the head and can cause warpage and even cracking. Verify that the fans, rad. cap, and water pump are working properly and don't worry too much about 100C as long as it doesn't climb much higher.

__________________

Gone to the dark side

- Jeff

The situation is perfectly normal with an older radiator.

You can beat the hell out of yourself and spend a bunch of money chasing it, but, in reality, the engine doesn't care.

See the red mark on the gauge? It's at 120°C. Provided you don't get up to this level, the engine will run perfectly fine and it won't cause any problems for itself.

My '86 has run up to 105°C. on a heavy upgrade in the summer. Do I look concerned...........???

My 87 300D routinely runs over 100C, sometimes its hit almost 120. Once Im moving it hovers between 80-100, but at a stop or hard up hills with AC on in summer it will get to about 115C.

Another thing, if you shut if off hot, then come back a half hour later in the summer the temp will be over 100C normally.

Dont know if this is good or bad, but its been doing this since day 1. Ive repl upper rad hose and water pump, maybe its time for a new rad?

__________________
Paul
Benz-less
I need an SDL !

Just for another data point, I've put about 5k miles on The Pimp Daddy and never seen the needle touch 100. 3,500 of those miles were on a desert road trip one week after we bought the car, and I checked the gauges obsessively (3-4 times a minute for the first 1,000 miles).

Only once has the gauge stopped touching the top of the "8" and gotten really close to the 100 degree line, and that was doing 85 up a 7.5 degree slope at 7,000 feet with the AC on.

We'll see if it's much different during the summer. So far I'm really impressed. Das Boot would often bump over 100.

__________________
2003 E320 wagon, ~80k, "Sputnik"
1987 300 SDL, ~160k, "The Pimp Daddy" (sold April 2010)
1984 300 TD, ~200k, "Das Boot" (Demised March 2008)

Think of it this way... the hotter the motor the better the MPG. to some extent this is true, take your T-stat out of a car and run a full tank of gas then put it back in and you tell me which got better mpg.

So say I've let the car idle with the AC on and the temp gauge is to the one mark beween 80 and overheat, should I be able to easily stop the belt driven fan with my hand?

-Jason

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

I would not try It.
Your viscous fan clutch MAY be working as designed,and your hand will not
thank you for the abuse.

EDIT:
Why would you want to put one of your hands NEAR anything MOVING in an
engine compartment? (No Answer required...rhetorical question)
(Boy.I've gotten grumpier over the last 30 years)

__________________
'84 300SD sold
124.128

Well it isn't fully summer yet! I would assume with another 10-20 degree's hotter outside the water temp. is also going to get hotter so I just am being precautions, call it preventative maintenance but I want stop free trips in the summer if you know what I mean.

What is the best mix of water/antifreeze for these cars in the summer? I know more water helps dissipate heat better.

What is your trick?!

LOL I was thinking that too, I remember reading a test one can do to test the fan clutch; if I find that article I will link it here... Speaking of which if I find a good article on the syringe + Toyota fluid to refill the fan clutch I will link it here as well.

__________________
'87 300TD Estate (Panzer Wagon, Sold)
'95 E320 Estate (Sabertooth, Sold)
'94 E500 (Stark 1, For Sale)
'04 VW GTI (Rhino, Sold)
'12 VW GTI Autobahn (Shadow)

Ummm, no. OM603 requires the T-stat to remain in place.

Removal of the t-stat will cause a short circuit of the water flow. Flow will go from the head directly to the water pump.

You can nurse your engine along without the t-stat, but the first time you load it, the temp will zoom into the scary zone.

Jim

__________________
14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

I wanted to address this comment separately and break apart your awesome diagnostic-al ideas. I broke your comment apart and put my responded in italic and [in brackets].

[Again as I mentioned before I just want to do some preventative maintenance. One would only assume so. Anyway I will check the circulating system however I would assume from what I have seen that it is running fine.]

Does anybody know if when the fan engages at high speed @ 105C does this considerably lower the temp. of the car back down quickly?

__________________
'87 300TD Estate (Panzer Wagon, Sold)
'95 E320 Estate (Sabertooth, Sold)
'94 E500 (Stark 1, For Sale)
'04 VW GTI (Rhino, Sold)
'12 VW GTI Autobahn (Shadow)

In reality, the ambient temperature seems to have little effect on the engine operating temperature. The '86 will run up close to 100°C. on a heavy pedal upgrade whether the ambient is at 50°F. or at 95°F. It's a bit of a curiosity, but the additional 45°F. makes very little difference in the engine temp.

The best mix is for water/antifreeze is always a compromise but 60/40 will likely do a bit better for you.

That's a bit of a loaded question. The answer depends on the conditions.

If the radiator is in marginal condition and the engine is creeping over 105°C. on the highway, the addition of the electric fan is not going to make much of a difference...........the engine already has considerable airflow and the radiator won't accept it.

However, if you're in city traffic with the a/c on and there is no airflow through the radiator, the addition of the fan will cause a drop to the engine temperature because there is no load on the engine.........the problem is simply lack of airflow.

Once you're climbing over 105°C. on a regular basis, it's usually time to remove and thoroughly clean or replace the radiator.

Mine does roughly the same thing Brian's does, everywhere he's posted so far. Exception: I'm using straight 50/50 water/antifreeze.

Get the engine good and hot on a hot ambient day. Get out as soon as you park somewhere warm and (after STOPPING the engine) spin the fan with your hand. if it resists you somewhat, and stops before turning for long, the clutch is okay.

If it free-wheels or spins for more than 2-3 seconds it probably needs replacing. mine did.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Let me rephrase... No, I'm not asking if I should try that. I'm asking if I should be able to do that easily, because I can. The fan is spinning slowly enough I can simply tap the blades as they go by with my fingers, slowing the fan wheel until I can stop it totally.

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.