Cooling fan issue

Hello! 
I've had some issue with my radiator fan not turning on. I have a 1.8 L K-jetronic with the 3 pin fan switch. When you bridge the contacts on the plug you connect to the switch the fan turns on. I tried installing a new switch (twice) and it made no difference.
When I felt on the radiator after overheating I noticed that bottom (where the switch is) was cold. 
Does this mean there is a clog in the radiator somewhere? Coolant does flow out when I remove the switch.

Thanks!
/TAb

Do you have an a/c equipped car?
as the AC equipped used a 3 speed fan switch and cable.
The non-ac used a 2 pin switch and 2 pin cable.
When you jumper the fan straight to the battery does it come on, and if the fan has 3 pins it should have a low and a high speed, the non-ac fan has but 2 pins

I would suggest that you remove the t-stat, and replace the cover with the hoses attached. collect the coolant.

Buy a new t-stat rated the same value as your radiator fan switch.  Drill a 1/8 inch hole in the lip of the t-state.  This allows any trapped air to circulate and eliminate the issue when filling the radiator.  

Remove the upper radiator hose at the engine and at the radiator, then using a garden hose and insert one end of a garden hose that is attached to a water spigot into the hose going to the block and run the hose. allow it to flow out the upper radiator end till clear, then reverse the hose to go into the radiator and out the engine flange till clear then repeat this about 3 times.  Drain all fluid, then insert a new-t-stat rated at the same temp of your fan switch.  

Tighten the bolts to 87 in/lbs.  Take the hose ends off the heater valve and the Butt-to-Butt connector and  ll insert hose to flush and back flush the heater core.  Drain, open the heater valve to full hot and reconnect the hoses.  Refill the radiator

Fill the Engine block first then the radiator reconnect the upper hose and retill the radiator till it dribbles out the engine flange reconnect and tighten the hose, and top off after running the engine up to temp and the fan cycles a couple of times, it it still over heats then replace the water pump..  

See:
https://www.volkswagenownersclub.com/threads/how-to-flush-your-radiator.21399/?post_id=418143#post-418143

https://www.volkswagenownersclub.com/threads/how-i-change-out-my-water-pump.21830/?post_id=739439#post-739439

The fan does run when hocked up to power.

I have already flushed everything and changed the t-stat while changing the switch.

Is it normal for the radiator to be cool around where the switch is?
Even when the coolant was boiling over it was still wasn't hot.

Is there a way to tell if it is your water pump? I have the fan wired to a switch and when I drive with the fan on it does not over heat, doesn't this suggest that coolant is still flowing through the engine?

Just went on a drive and it was running quite hot and now that I think about it there could be an issue with the water pump. 
Is there a way to check?

Another update:

I tested the water pump by removing the return hose to the radiator and starting the car.
There was coolant coming out but unsure if it is enough?
The picture is how much came out when on idle.  

When in doubt just replace it.  It isn't that bad to replace the whole thing housing and all.
You have Piece of mind that it will only last another 10-years.

But drill a hole in the lip of the t-stat as you  can have the air bubble from hades, with the hole in the t-stat that will never happen.

Here's how I do it on my Cabriolets or any mk1 with a/c.  
https://www.volkswagenownersclub.com/threads/how-i-change-out-my-water-pump.21830/?post_id=739439#post-739439

The fact you are getting some coolant flowing out through that hose is possibly a good sign, but the volume of water would probably vary depending on what state the thermostat is in - open, closed or partial.

There seems to be dearth of information on the route the coolant takes. The diagrams in the link below sourced from a VW publication from 1973 are the best I've found, at least to provide a general overview:

https://www.vwvortex.com/threads/help-with-the-coolant-flow-routing-logic.7007214/

Thx for the replies 
Didn't think about the t-stat effecting the coolant flow…
I feel the pump is working fine, I have also driven a bit more running the fan manually and it seams to work fine.

I have drilled a hole in the t-stat.

How would coolant flow through the radiator normally?
With the inlet and outlet on the same side the only way I se that makes sense is it flowing from the inlet side to the other side on the top half of the radiator then back on the bottom half? 

From the Cabriolet Bentley,



Flow is going one way or the other…

There is what we call a bypass a feed in, and a feed out.

Basically there is a t-stat that has to get open for full coolant flow and until the t-stat pops open it has to have a bypass route (restricted flow so the system don't blow up.

What ever direction you like, it don't matter as the radiator has to tanks to hold coolant one on the left and one on the right.

Coolant flows from one tank to the other through the radiator core or matrix.  in on one side, out on the other.
As it passes over the Matrix or core, it has air flow over the core or matrix and exchanges the heat off the system buy pulling air through the matrix

When you are moving there is normally enough air flow to maintain stable temp of the coolant that is being monitored by your fan switch to hot and the switch turns on the fan.  You see it most in Stop and go traffic, or stop after running down the highway, as when you stop the temp will rise a bit and the fan engages and cools it down, also when you park your car.

Here are the Critical bits that I still don't know.

Is your car fitted with Air Conditioning. as in specific model.

if no, then do you have a 4 speed heater blower fan switch inside or a 3 speed heater fan blower switch.

WHY?  Because that tells me if you are having issues with the Fan Switch relay

And you stated that you have a 3 pin fan switch in your radiator, 3 speed switches are for AC, and have a high side and a low side.  Low side for normal, and a high Side for a/c operation…  

If you have 2 wires going in to your radiator fan switch you could be on the wrong side and if you are then your car will not turn the fan switch on unless it is way tooooooooo hot.

2. If your radiator fan switch rated at the same Temp spec as your t-stat.  
see the below link to a table for the cabriolets or mk1's
with and with out air,

https://www.cabby-info.com/cooling.htm#Refill

Do you have the Baffles on the Radiator, as the upper one is most critical for proper operation of the system as it prevent the air in the engine compartment from re-cycling over the radiator. Specifically at a stop.

Here is a Trick I did to my radiator shroud to make it easier to remove.

Normal shroud.



Marked for cutting.




Here is what it looks like after the trimming.



Also the flaps on the Shroud should be free to open and close.  As when the fan is running they pull in to close the engine compartment air off and only allow fresh air in over the Matrix and out.

If there are things running near then that can interfere with the cutoff of air flow.

If they are always open then you r car can suck in engine compartment air If they are restricted from opening then you can get normal air flow over the radiator when running down the road.

Though It would be easy to answer?

Everything I  ever thunked I knew about radiators/fans but was afaird to speak.

https://www.volkswagenownersclub.com/threads/radiator-fan-operation-explained.54346/#post-504978

Thank you for your continued patience.

I do not have air con, the heater fan switch has 4 speeds and the switch have a matching.

I still don't really understand how the coolant flows through the radiator since the inlet and outlet are on the same side and what looks as the same tank? How you described it it seemed like the inlet and outlet where on separate sides.

Currently it is wired up like this



If my understanding is correct this means that the switch in the dash act just like the standard fan switch would if everything worked properly, but since i have switched the fan to a brand new one twice i really don't believe that this is the problem.

So unless have misunderstood how the fan switch works the issue is that the coolant touching the switch is not hot enough to activate it.
This would mean that either the hot coolant is not flowing correctly trough the radiator.
Or the coolant is not getting hot and the engine just isn't cooling properly, however this would not explain why it does not overheat when i run the fan manually?

 Whats this about a fan relay? I tough the fan only was controlled by the temperature activated switch?

What is the year of your car?  as you have to have the right schematics as. you have a 4 speed fan switch in the Heater controls, and a 3 pin radiator fan switch
Does your fan have 3 pins on the connector or 2.

Take a photo of where you alternator is and what is below it?  

AS it appears some one frankensteined it.  

So further information is needed.
The to the right side as you look at the battery is there a relay attached to the inner fender?

Are you sure you have no air locks? I usually run the engine up to temp with the coolant cap off, and I give the top and bottom hoses the odd squeeze while waiting for the engine to get up to temp and the T-stat to open.

You will know when you're getting there as the top hose will get hot - the water flows in the engine through the bottom hose and returns to the rad via the top hose.

While doing this have the interior heater set to hot, and you should feel both the heater hoses getting hot as the water flows through them, into and out of the heater matrix.

It sounds like you may have a sludged up radiator if the area around the fan switch doesn't get hot - it should do, otherwise the fan switch can't do its job.

The coolant fan needs to run via a relay as it draws a large amount of current.