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Discussion Starter #1
Having trouble removing electrical connector. There's a tab?

Wayyyy tight space in there for a 29 mm, deep socket??

Is there any real reason I can't just take the old one out, deal with the coolant spilling out, replace switch and top-off radiator?

Any tips on this procedure?

Having to drain the entire cooling system and/or trip to mechanic seems a bit much. I just had the coolant flushed six months ago.
 

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If you have to change that switch, I don't see any way you can do it without having a coolant spill mess, unless the coolant is drained first. Just get a (clean) container, such as an oil drain pan, then find the red drain valve- there's a short stub discharge tube; fit a suitable hose to that and direct into the pan. Open the red valve knob a few turn, loosen the reservoir cap, and begin draining. You can re-close the drain to dump coolant into a better container occasionally, if needed. Use the correct method to refill and bleed out air, in particular don't run the engine while purging air.

I remember that connector being difficult, and the location inconvenient. Why are you changing that switch?
 

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Discussion Starter #3
As mentioned a bit in another thread, the relay (one of the "370s" near the brake pedal) associated with the aux electric fan has been chattering for years. Fan turning on and off randomly, but not reproducible while at mechanic.

As the switch, probably, gradually deteriorated, last summer the fan would occasionally stay on and not shut off even half hour after turning the engine off. I had to disconnect battery, pull fuse, or remove relay to stop the fan whenever this happened.

I tried a new relay. Still chatters.

Next, I noticed parasitic drain of a little less than 1 amp, IIRC, and that was killing the batt.

Even the parasitic drain seemed to be transient. On the occasion I checked the drop on all fuses, I did not see the 1 amp draw at the battery, and no drop at the fuses (all fuses ZERO voltage drop except for miniscule expected voltage drop at the fuse for the factory security system, I think it was only 1 milliamp, suggesting no parasitic drain at all (temp switch was not mis-behaving at that moment?). Later, the drain seemed to be happening again as something was killing the battery, even with the relay removed.

Recently, with the relay installed, the chattering was off the hook, like a continuous buzz, which was suddenly increasing in intensity with throttle input, which never happened before. I guess it is just getting worse. I removed the relay.

I understand the temp switch on the rad is the likely culprit.

In lieu of long trip and multiple days at my favorite mechanic, no one local wants to just put the switch in for me, so I have to do it myself.

So far, I have not been able to pop the bumper lower valance/grille out to access drain cock and/or the red valve (I suspect 1999 AEB has the drain cock). The valance isn't popping out, I am yanking on it, worried about cracking the valance.

Yesterday, while trying to work connector off, I was thinking, why can't I just let the coolant run out of here instead of completely draining the rad. The switch seems to be about 1/3 from the bottom of the rad, so why drain entire rad. The whole system was flushed just a few months back.

I also need to find the right socket deep enough but also with enough clearance for this, which is another problem.

Really frustrating because it seems like such a simple thing, and yet it is causing so much havoc. Most mechanics are going to want to go fishing for an electrical fault instead of just changing the switch and seeing if that works, but it's a 21 year old car. Local gas station didn't want to just change the switch and replace the coolant on my assumption of risk that would not solve the problem. Just didn't want to help.
 

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well, if you disconnect it and all the problems stop, then you can be sure that is the issue...
 
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I tend to agree that the radiator switch is probably why the relay chatters. The switch should have a bi-metal dome that clicks one way or the other, depending on how hot it is. Such things crack, preventing them from snapping as designed, so it may be making marginal contact that doesn't give a solid 12V to the relay coil. Since that switch is mostly a redundant feature in case the mechanical fan isn't doing it's job, try getting it disconnected and see if the relay stops chattering. By the way, the relay chattering will quickly burn and pit the contacts.
 

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What do you need the socket for? It's held in with a clip much like the normal CTS (at least it is on my AUG engine). I pulled the switch from the hose with the connector still attached, then removed the connector while I had better access to it. It's in the lower radiator hose, you can see the opening in this pic with the front end removed:
101040
 

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x2 on the posts above.

My 2 cents worth: the temperature switch is the same size as the coolant temperature sensor, and also has 4 pins. In fact, for a while one of the third-party parts databases had the parts mixed up, which caused all manner of pain. (The sensor contains two thermistors, the switch two switches. Physically interchangeable, but definitely not electrically!)

Unplug the switch connector and see if the problem goes away. The fan will still run in low with the A/C on. You can look at the CTS to see how the connector goes on and how the clip holds it in place. Don't use a socket...
 

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The confusion may be coming from some listings that show the coolant temp switch as a screw-in one like found on the A chassis VWs and B4 Passat.
101050
 
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That's the coolant temp switch that I was thinking of, certainly was on my '96 A4 and I thought also on our '99 AEB wagon. RechtsFahren appears to be describing that same thing, instead of a temp sensor.
 

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That's the coolant temp switch that I was thinking of, certainly was on my '96 A4 and I thought also on our '99 AEB wagon. RechtsFahren appears to be describing that same thing, instead of a temp sensor.
Yeah, I can’t quite tell which one it should be in that year. Best way is to snap a pic.


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