1971 300SEL 3.5: aux fan not working

[sjefke]

Martin, take the old switch out and clean it first. It is very unlikely, but it may have bad contact due to corrosion. Also try tapping it. Not sure whether it is a springloaded bimetally thing or so inside, but something may be stuck inside. It's worth a shot. Soldering irons are also a quick way to heat something in a controlled manner.

Bert

[werminghausen]

Originally Posted by sjefke

Martin, take the old switch out and clean it first. It is very unlikely, but it may have bad contact due to corrosion. Also try tapping it. Not sure whether it is a springloaded bimetally thing or so inside, but something may be stuck inside. It's worth a shot. Soldering irons are also a quick way to heat something in a controlled manner.

Bert

I have 2 old switches (tomguy said for the 4.5, pic 3 earlier)...with some cracks in the top seal. I tested both with boiling water and unfortunately...no life. Both tested negative....no continuity at boiling temperature. So far the old switches are dead.
I can start tapping them and test again. I can also open one up and see what is inside... I saw a small screw while peeling the sealant on top off...maybe an adjustment screw for changing temperature range?

[sjefke]

Just get a new one. I think they are around $20 or so (at least last time I checked). Mine is also busted but since my car never overheats, I never had the urge to replace it.

Bert

[whunter]

Originally Posted by werminghausen

Thanks Whunter
quite expensive this beast? I'll look for something here in Oman and Araboan desert...but not easy. Do you think the switch I have (third picture) might work? Other wise I 'd just jump the temperature switch for the AC and keep the auxfan running permanently.

I also found that my engine is overheating a lot if I get stuck in traffic.
I easily reach 220 and over close to the red mark. What do you think this is?
Also starting the engine becomes problematic if the engine is overly hot..
What is this?

martin

Sounds like:
* A bad thermostat.
* The radiator and cooling system need a serious citric flush.
* The water pump is damaged.
* The head gasket is failing.


.

[werminghausen]

Originally Posted by whunter

Sounds like:
* A bad thermostat.
* The radiator and cooling system need a serious citric flush.
* The water pump is damaged.
* The head gasket is failing.


.

Thanks,
I will replace the thermostat....I can't remove the water pump right now.
radiator citric flush: what is this? What chemical is good for this?
muriatic acid, vinegar?
Would you flush the radiator only or entire system?

[whunter]

Originally Posted by werminghausen

Thanks,
I will replace the thermostat....I can't remove the water pump right now.
radiator citric flush: what is this? What chemical is good for this?
muriatic acid, vinegar?
Would you flush the radiator only or entire system?

Proper procedure for flushing radiator

citrus flush causes all this hard white chalk in my cooling system?

Citrus Coolant Flush?

Going to do the citric acid flush next week, quick question

Radiator citric acid flush


.

[werminghausen]

Originally Posted by whunter

Proper procedure for flushing radiator

citrus flush causes all this hard white chalk in my cooling system?

Citrus Coolant Flush?

Going to do the citric acid flush next week, quick question

Radiator citric acid flush


.

Thanks so much, very helpful.
I guess I'd need 1# of citric acid and 2 gallons of water for the acid flush?

[werminghausen]

I was testing all my temperature switches (I have 4 now total) and none! of them is working. I'll attach pictures.
I was testing in a pot of hot boiling water....
Procedure: measuring continuity between body and pin.

None of the 4 100C switches worked. A brand new switch my son brought from the US failed the test as well. It shows continuity all the time...cold and hot... URO should be banned. Their products suck big time and I don't know why ******** is using them (I had a ignition switch fail on one of my cars...brand new URO...had to tow the car home)

All my 3 old switches were failing the tests too. There was no continuity at boiling temperature.. Now there could be the chance that these 3 old switches open at a higher temperature...at 103 or 105C for instance but how can I test this?
Is there a common liquid that is boiling at 110C?
Is there anything that can get stuck in the old switches that might open up by tapping. I need to get one switch going at least and I can't buy one here.

Martin

[werminghausen]

I was ripping apart the two switches I had with the big 'belly' in top.
They have a fine gear inside with a points that closes when an expanding element is triggering the switch at 100C. I'll attach a picture.
Both trigger points worked well but the expansion elements are dead.

I then tested my old switch and found that it worked if I use a torch heating up the switch -of course this is dangerous because of the risk of overheating.
So this switch still worked...maybe at slightly higher temps than the 100C as is didn't work at boiling temps.
The new URO switch is trash from the beginning. URO should banned in my opinion. Cheap but not worth the effort.

Now I was trying to search for the culprit.
I found the AC fan relay was dead...it was 'burned' inside.
Where do I get one of these good old relays?

Here are pics.

[werminghausen]

It seems to be difficult to get one of these relays?

[Tomguy]

I can't tell if the physical pin layout of this relay is the same or not. Pelican, The Classic Center, and any MB dismantler will surely have an abundance of the relay you need.
Pelican Parts - Product Information: 001-542-02-19-M504

[Mike D]

A Relay is a relay is a relay. The ONLY difference would be a 5 terminal relay and about the only place I've seen them used are in lighting applications.

You have 4 terminals. 1 is for battery power, 1 for "switched" voltage, 1 for ground/earth and 1 for supplied power.

A little work with a soldering iron and you can replace the old canister style mechanical type with a newer electro-mechanical model available at any automotive part supplier.

The aux. fan is activated by completing the ground/earth circuit which is what the 100C switch does.

You should have 12V on one terminal constantly, 12V with ignition "on", continuity with ground on one and the other is the power supply for the controlled device.

You can buy relay sockets to install to make the whole conversion look a bit less "hacked".

Don't ask me the terminal numbers are on the relay (31, 87, 87A, etc.) because I never can remember and always have to dig out my notes. You can find the wiring notes on the web. Just search for "voltage relay wiring schematics".

[whunter]

Originally Posted by werminghausen

It seems to be difficult to get one of these relays?

Relay
MB# 0005429719
This is no longer available.
No after-market production at this time.

.

[werminghausen]

Originally Posted by whunter

Relay
MB# 0005429719
This is no longer available.
No after-market production at this time.

.

Thanks, anyway in Oman I think I have no chance to get this relay.
MikeD mentioned I could use another relay (I have one of these cube relays from my Bimmer) and tweak /solder this one into the base plate (the 4 pin plate)
However it will be tough to get the old look with the cylinder?
Did anyone successfully convert the old relay and keep the old look?

Martin

[Mike D]

Found my pin out note on the relay.

Terminal #30 High power feed (needs to be fused)
Terminal #85 Relay ground (this is the one to connect to the 100C switch)
Terminal #86 Relay feed (ignition ON feed) (trigger wire)
Terminal #87 Output supply-normally open (used in 99.37% of applications)
(Terminal #87A Output supply-normally closed (rarely used))

I don't know how you would go about changing the newer style housing into the older round canister style. I don't think it can be done. I have shoe horned the newer styles into the elongated metal cans but it was a pain and I'd never do it again just for "originality".

So, the always "hot" wire goes to terminal #30, ground/earth/100C switch (use an ohmmeter to check continuity with the 100C wiring harness) terminal #85, ignition trigger wire (12V when ignition is on) terminal #86 and fan power feed terminal #87.