One more question,
My inner platic fan shroud is more then 50% missing. I have read that a mangled fan shroud actually makes a huge difference? Is this true? Should this be something else I should consider replaceing as well?

Also, when are the two auxilary fans supposed to come on? Even though the coolant temp is >110C, they electronic Aux fans still didn't engage. I beleive only one comes on when the AC comes on. Is the other Aux fan a emergency cool fan for when the coolant gets blazing hot?

No. The clutch just slips less when its hot. It's job is to keep the fan spinning, but not allow it to exceed some RPM or the fan would fly apart.

-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.

Last night I jumped the AC pressure switch on my 300D while the car was running and the two front Aux fans did turn on. When I then plugged the leads back in, and turn on the AC, the fans did not turn back on.

How does one properly test the two switches/ sensors for the Aux fans? I also checked the fuses, but since the fans turned on while they were jumped, I know that the wiring and fan motors are working and the fuses are good. Is it worth the time to try and troubleshoot anything else, or should I just replace the two sensors?

__________________
1990 300D 2.5 Turbo 150k miles
1999 F250 7.3L Powerstroke 225k miles 22mpg
Intro Thread

The electric fans turn on low speed based on AC refrigerant pressure (the red switch at the drier, behind the driver's headlight). Short the leads of the red switch, the fans should turn on low speed. The fans turn on high speed based on the signal from a temp sensor on the cylinder head (it's a sensor, not a switch!). At about 105°C, the fans should be on high speed. If not, you have a fan problem - could be the fuse, relay, fan motors, sensor, etc. Not too hard to troubleshoot though.

The fans should always run at the same time (left + right). If not, one or the other is bad. I'd consider replacing both since the other is probably not far behind. New OEM/aftermarket fans (000-500-85-93) are about $125/ea, or $230/ea wholesale for OE/dealer fans. Or check with Potomac Pat for used ones.

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

If the clutch is engaged, it will stop within about 1 second when the engine is killed, and I mean STOP, not spin down. I need to take a video of mine. The video above is sort of in between... the fan stops in about 2 seconds, which isn't great, but not that bad either. I'd compare it to a cool shutdown (at 85°C on the gauge). When not engaged, the fan usually spins longer, but the best benchmark is to view the same clutch / same engine at a warm shutdown (instead of a hot shutdown).

The usual problem is determining why the clutch isn't engaging... even a new clutch won't engage if there's not enough heat coming through the radiator fins (due to airflow blockage, poor coolant flow, cold spot on radiator, etc). But when the engine temp is 100*°C or above, the clutch SHOULD be engaged - if not, something is wrong (probably the clutch, but not necessarily the clutch.)

Not Electrical !

You have Low Speed Fans from the Reciever/Dryer Switch to the Fans
(So that's O.K.) If your Refrigerant level is LOW the switch will not trigger AND
the A/C Compressor will not operate, also.

The High Speed Fan Switch sensor is Screwed into the Top Radiator Hose
Aluminum Fitting on top of the front of the Head. With the KO (Key On) unplug
the Two Pin connector and the Fans (Auxiliary) High Speed SHOULD operate!

EDIT: (Through the kind services of GSXR's forum correction)
I must point out BOTH of the below statements are Incorrect!

"The Blue Plastic insert Switch DOES NOT OPERATE until 130C !!!
(You can get a Red Switch MB part #006 545 40 24 with a 100C operating Temp.)"

CORRECTION:
MB # 008 542 45 17 (Blue Two pole SENSOR) operates as low as 107 C.
AND MB # 006 545 40 24 is a SWITCH not a sensor...SO the two are not
interchangeable!


BUT If you're seeing high temps (On an almost 20 year old cooling system)
1.Thermostat [Tested off the car in boiling water]
2.Radiator (AND Condenser) cleaned of all the crap accumulated!
A cool spot in front of the Viscous Fan Clutch will Guarantee it does not engage!
3.Citric acid flush
4.New Radiatror

__________________
'84 300SD sold
124.128

Only the 1986-1987 models use a temp switch for the electric fan (switch = on or off). Your 1990 model has a temp sensor for the fan (sensor = variable resistance based on temperature). I believe the temp sensor for your 124.128 chassis will be 008-542-45-17, but you may want to verify that (the number is stamped on the side of the housing in teeny tiny numbers).[/B].

The FSM indicates that the high speed (2nd stage) electric fans should engage at 107°C, Group 83-600, page 27-30 in this PDF file.

The 1986-87 switches all turn on the fan second stage (high speed) at 100-105°C. The higher temp rating (128°, 120°, 115° depending on the "color") is only for the safety cuttoff of the AC compressor, NOT the fans.

My one car (with the 606 turbo clutch, 606-200-01-22) when engaged, stops immediately - I mean, in less than 1 second, it jerks to a screeching halt. When not engaged, though, it still stops darn quick - spins to a stop in about 2 seconds. The difference? When not engaged, you can rev the engine to 3000rpm and it's obvious the fan isn't turning that fast. When it is engaged, at 3000rpm the fan is deafening. I mean LOUD.

What's interesting is that on my other cars (with the 606-200-00-22 clutch), it's not quite the same. When not engaged, they take 5-8 seconds to spin to a stop. But when engaged, they stop within 1-2 seconds... it's a much bigger difference between engaged & not engaged.

Bottom line - if you're not sure if your clutch is engaged, try the "roar" test... get the engine hot and then with the hood up, rev the engine to 3000rpm. If the fan noise doesn't drown out the engine noise, the clutch isn't engaged.

I really need to get some video of this!

Allright,
Not alot of time, but did lots of stuff over the last few days. I did the 602 to 606 fan and clutch mod this last weekend, here are some pics:


Not as tight as the 603, but the stupid fan shroud is still a major pain


No special tool needed for the 602 engine


Despite no special tools, it was still a pain to loosen the main clutch nut (8mm) beause you have to work through the fan blades, I guess if you had the $100 MBtool this would be easier.


Pulled the radiator out and sprayed it down cleaning all the dead bugs out and stuff, it really wasn't that bad, you could easily see sunlight through it before cleaning and the water easily flowed through the fins


Also cleaned the Condensor with hose and air pressure


New waterpump and fan also installed


Scraping the old water pump gasket off


New water pump installed. Bolts (7 of them) torqued to 10Nm


109 fan from Junkyard, 602 fan, and new 606 fan all side by side


602 vs 606 fan side by side. The fan and clutch were both aftermarket parts at great prices $50 for fan and $100 for the clutch, both made in Germany and the quality felt and looked REALLY good. I was suprised.


$9 Harbor Freight tool holting water pump pully while tightening Fan clutch nut to 45Nm. The Harbor Frieght tool is cool because it is not only cheap ($100 for the MB version) but the nub is adjustble, so I can actually spin the crankshaft pulley with it while the fan shroud is on, so that saves me from having to pull the fan and fan shroud when ever I need to manually spin the motor


This was tricky trying to torque the fan nut again, as my longer .5" drive torqure wrench needs a 3/8" adapter on it to fit my 8mm allen socket, so I had to use my 3/8" torque wrench and it wasn't long enought to really grip without leaving skin on the radiator. I ended up leaving skin the radiator


Back together, I'm going to flush the system a few times, and use RO/DI water when I fill her back up to keep the mineral deposits down, and once I get the Aux fans worked out, I hope my running hot days will be history! (Just in time too, working in Mojave CA and then driving home from work takes me from 2500, to 6500, and its starting to get hot, so last week I had to drive with the windows down and the heater on to keep the Ol gal from running too hot. Not fun with the temp outside is in the dry 90s and Mojave windy (40knts)

Waiting on parts to check my engine timing, but hopefully I'll get them tommorrow or the next day and I'll be able to figure out my rough running engine.

__________________
1990 300D 2.5 Turbo 150k miles
1999 F250 7.3L Powerstroke 225k miles 22mpg
Intro Thread

I have good AC performance, and AC pressure is good. What are the chances that both the low speed switch and the temp sensor is bad? Obviously jumping the "sensor" will not turn on or off the high speed fan, so is there another test I can perform before replacing the sensor or just R&R the sucker?

__________________
1990 300D 2.5 Turbo 150k miles
1999 F250 7.3L Powerstroke 225k miles 22mpg
Intro Thread

Also there was a slight amount of oil in the cooling antifreeze. Is it possible for a diesel to run fairly decent with a small weeping head gasket leak? How else could oil get into the cooling system? Will a compression check reveal a slight head gasket leak? I've never done a compression check on a diesel, I assume you need a diesel pressure rated gauge, and then check it through the injector ports?

I hope not I hope not, I hope not, I hope not, I hope not... if thats the case, the misses is REALLY not going to forgive the car as it will likely take me a few weeks to replace the gasket. What about this cylinder head cracking from the head getting too hot, I understood that was mostly an issue with the 603 motors, anyone know of that happening on a 602?

__________________
1990 300D 2.5 Turbo 150k miles
1999 F250 7.3L Powerstroke 225k miles 22mpg
Intro Thread

I shop here on fastlane for some parts I can't get elsewhere but the absolute best is a u t o h a u s a z.

Free shipping on orders over $50 and they have the best prices and selection anywhere.

I will place an order on Sunday night and sometimes have it by Tuesday, with FREE shipping.

Very hard to beat.

__________________
1993 W124 300D
-297K on the clock as I type this.

It can run just fine with a minute oil leak into the coolant. If we're talking a drop or two of black oil floating around the coolant reservoir, don't lose sleep over it. A compression test may or may not reveal a problem. You need a diesel compression tester and the test is typically done through the glow plug holes, since the adapter for the fine-thread injectors is not common. The 602 engine is known for blowing the head gasket in front of the #1 cylinder, but the usual symptom is blue smoke and oil consumption. BT, DT.




The cracked head issue affects the 1986/1987 OM603 engines with original heads only, they had a casting flaw which was corrected in the late 1980's. I don't think I've ever seen a 602 with a cracked head. I'd flush the cooling system with a cleaner to remove the oil trace, re-fill with MB / G-05 coolant, and keep an eye on it. I've ended up with a trace of oil in the cooling system even after replacing the head gasket on two different engines - but it was never enough to make me re-do the job (and, I wasn't sure if it was leftover oil in the system that I didn't get flushed out).

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

Since your fans work when you short the lead at the red switch on the drier, the red switch is almost certainly bad. Problem is, the AC system must be evacuated to replace the sensor, then vacuum pulled, and the system re-charged. Probably best left to an AC shop, since I doubt you have the equipment required.

I'm betting the engine sensor is also toast, at ~$20 it's best to just replace the silly thing. A proper test would involve plugging in a resistor (say, 150-200 ohms) into the connector to simulate high temps, and see if the fans turn on high. If not, I'd suspect the relay or wiring... but that's not likely.