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I'm confused, have you seen any improvement? I unclogged my heater core recently and I have 160 degrees coming out of the vents of my 2003 1.8T. What kind of temps are you getting from in the vents? That should give you an idea of heater core performance.

What exactly did you replace? It says "tried/replaced" in your list, did you mean both? Big difference between the two. For example I've read some B5 water pumps will fail soft so like if you're going down the highway the car may start to overheat before you ever encounter anything similar in normal traffic. The impeller may be missing blades or may be clogged with crud. It could be there and working but it can't keep up.

The flush tool mentioned in my post can be used on other parts of the coolant system besides the heater core, some people use it for the entire system but the thermostat must be removed to do that. I'm skeptical how effective it would be. If my radiator were clogged I would probably try to attach directly to same way I did with the heater core, if that's possible.
 

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Discussion Starter #23
Here's everything I did:

Replaced:
Timing belt, water pump, thermostat. Radiator fan switch.

Flushed heater core with CLR, water and air. Flushed the rest with a commercial flushing product from a parts shop. Drained, flushed with water. At that point it stayed steady at 210F (without driving it).

Drained, reconnected the heater core, refilled with coolant and bled. Stayed steady at about 225F and had heat! No fan. Drove it and immediately overheated. No fan.

Fan works when turning on AC. Temperature drops when revving.
 

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Discussion Starter #24
Did you try jumpering the coolant temp switch pins to simulate a closed circuit? That should activate the fan and confirm whether you have a bad fan module or bad switch/wiring.

You got this one, right? https://www.ecstuning.com/b-genuine-volkswagen-audi-parts/auxiliary-fan-switch-4-pin/8d0959481b/
No I did not try that but I did confirm the fan is good and it's a new switch, so I guess it could be bad wiring to the switch I'd have to check that when it's cooled off.

Yes that's the switch I got.
 

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The 160 is what I got from the vents at idle after it warmed up. I should note even when the heater core was clogged the car did not overheat. The heater core is supposed to have a bypass in it in case it gets clogged so that the coolant can keep flowing even if it doesn't make any heat. I used an Infrared Thermometer gun (like a laser pointer) to measure the temperature inside the vent, the generic orange ones cost about $20.

I would try driving it with the heater core bypassed and see if you notice a difference.
 

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Discussion Starter #27
Ok update, please weigh in.

Just bypassed the heater core again. Car is holding steady at 208-210. Still no fan.

I think I'm gonna go for a quick drive and see if it stays steady?
 

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Discussion Starter #29
97851

Just went for a drive. Maxed at 223F, parked and it creeped back down. I assume it would have come down more quickly with a working fan.

What am I doing wrong!? 😣 Maybe I didn't bleed it properly any of the 62 times I tried? Doesn't seem possible...
 

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Discussion Starter #30
At this point I'll accept putting in a toggle switch for my radiator fan. It's all for naught though if I can't get heat. I'm not driving this in Maryland winter without heat. I've heard over and over though that a clogged heater core will not cause overheating, so what about my heater core IS causing the overheat then?
 

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Just a thought, at some point in time, crap ( plastic water pump parts,who knows what else floats around in these cars) and has been acknowledged ,the brown sludge has permeated the system, I would say your radiator is clogged not allowing any flow. Your fan will not come on as the temperature never gets high enough to activate the sensor do to it's remote location by bottom of radiator. Learned on forum not to just throw money at stuff but in this case I would suggest buying a new radiator but only after flush of the system a few times. That flotsam and jetsam makes its way to your turbo that will be a whole different problem.
 

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Discussion Starter #32
I believe your are right! I just unplugged the fan switch and plugged it into the removed switch. I heated it with a heat gun and my fan turned on!

I don't know why I'm excited. I think this means it's time for a new radiator. That's a bit disappointing. I may need a heater core too. I have flushed both and only got a slight improvement. Is it worth continuing to flush?
 

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may have to do heater core with some CLR and "swish" it back and forth and then independently clean/flush engine, might have to remove thermostat housing to do this effectively......definitely worth the effort versus HC replacement, I got a "Nissens" and am happy with it.......a "cool" engine is a happy engine
 

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If memory serves, my dealer used Shout laundry stain remover (large bottle, say 64 oz) to clean out cooling systems that had been gunked. My now indy mechanic says he now uses alternating cold and near boiling water to flush clogged heater cores (probably after the Shout, to remove the oily mess).
 

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Discussion Starter #36
If memory serves, my dealer used Shout laundry stain remover (large bottle, say 64 oz) to clean out cooling systems that had been gunked. My now indy mechanic says he now uses alternating cold and near boiling water to flush clogged heater cores (probably after the Shout, to remove the oily mess).
I'm gonna flush my heater core with a bit more pressure than I did last time, after letting the CLR sit in there for a few hours.

Anyone see a problem with leaving CLR in the heater core say overnight?
 

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you probably need to flush your radiator now that your heater core is clear...your heater core is acting as your radiator...so if you're driving it, cranks the heat as high as possible.
 

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Discussion Starter #40
So I've had an awesome day.

Went way out of my way to get a radiator from an Advance Auto in stock.

Got to the car, started disassembling and got the radiator out. Pulled the new part from the sealed box and...

97859

Old part

97860

New part. See anything wrong?

Yeah the oil cooler on the passenger side is missing! I searched a bunch and the part number on the box and on the part was correct. I had to call a few other stores up to 50 miles away to get them to open what they had. After 3 others that were not correct I found one 40 miles away that was right. Just got home from swapping them out.

So I guess I didn't get it done today. I did fill the heater core with CLR and water. Hopefully it's nice and clear by the time I flush it out in the morning.

Anyways, if any of you are buying a radiator from Advance be sure to open it in the store and check it.
 
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