Start with checking the fans. Does the engine driven fan have any resistance to a gloved hand? Carefully try to slow the fan down, if the fan clutch is bad, it will stop spinning and may not start right back up. Does the electric fan come on with the a/c, does it run slow or fast?

Was the coolant changed with the water pump and thermostat? Is it still pink and clear?

Is the fan shroud still in place in front of the radiator?

 

HI PZ,

Thanks for the insight here. I will look at this when my fiance gets back with the car and get you some answers. The coolant was changed when the thermostat was changed. I just drained and refilled it to do the coolant flange a couple months back.

 

FWIW, I had similar symptoms and it turned out to be the radiator. However, my heater core was clogged when I originally bought the car and I suspect the PO used 'stop-leak' on the car to try to fix some of the typical coolant leaks seen on these cars. Like PZ says, I'd start with the fans but if everything else checks out a clogged radiator can act like this.

And be careful with the car until you get it fixed. I drove mine like this for years since it only happened on rare occasions and the temp could be controlled by backing off the throttle or AC. Then one day my wife had her parents in the car to show them our old house in the mtns. It was a hot day and she likes the AC on high. The car over-heated and long-story-short, I had to replace the head on it after that.

 

Hey yall, I finally got to looking at the car today and I checked the main fan and it was spinning strong. Also when I turn on the AC fan it turns very fast so I dont think that is the problem.

Any other recommendations on what to check?

 

A thought.....are you adding ANY coolant/water occasionally?...Is it possible there is a small leak somewhere, not known, possibly mistaken for AC water? I had a pinhole leak around a deteriorating heater core, would drain into battery compartment, dribble down around ac puddle. Pressure escaping under stress might allow temp to increase, momentarily, acting like coolant cap is loose...not wishing bad things, but check oil cap for dirty shaving cream residue.....possible head gasket.

If not adding, leaning toward crud in the system, either in, or in front of, radiator......

 

No CEL? If there is, check the fuel trims as a lean running engine will run hot.

If not, with the fans, T-stat and pump all working, coolant flow through the radiator and airflow through the radiator are your two choices. I have seen dirt and grime plug a radiator externally, usually between the a/c and radiator, but I suspect the coolant flow in the radiator is the real issue. Turning the a/c off will probably allow the radiator to cool better, but will not help you any. Usually you test the radiator by tuning on the heater to dissipate heat the radiator can not, but that gets uncomfortable in the summer heat.

I would check the radiator hoses when the car is running hot. The upper hose should be burning hot, the lower hose should also be very hot. If the lower hose is cool, either the thermostat or radiator is the issue. If it's warm to hot, usually that's a bad radiator. You could try a cooler rated thermostat, but that might affect mpg slightly. A replacement radiator is not expensive, running about $75 shipped for the cheapest to $100-110 for the better ones on Ebay or Amazon (Nissens, Behr).

https://www.fcpeuro.com/products/audi-volkswagen-radiator-a4-quattro-passat-behr-8d0121251bc

https://www.europaparts.com/radiator-8d0121251bc.html

https://www.rmeuropean.com/Products/8D0121251BC-MFG75.aspx

 

I do find that after a couple months the coolant does leak but its very slow. I am not sure where from though. I do notice if I look under the car I see some water on the underside behind the front passenger seat location. Not sure what that could be from. I smelled it and it had no smell so im assuming coolant/water from AC.

There is a CEL but it is for the p0411 SAI Pump code I dont care about as I dont need emissions testing where I live.

 

The a/c drain is at the firewall in front of the passenger seat, so that should be water.

The CEL will cut boost, which would require a lot more throttle to climb the hills. That may be the reason for the higher coolant temps. It would also hurt mileage when power is needed as it effectively cuts compression.

I did drive my 1st Passat 1.8T home from Virginia with a CEL one year, there were no overheating issues, but it was only a 3 year old car at the time. It ended being a vacuum leak that rubbed through after some body work was done.

 

Quick question pretty unrelated to this post, but would pulling the fuse for the SAI pump limit boost as well since it makes the car throw a CEL?

 

Thanks for the info here. I am trying to look at the P0411 code but its been raining the past week so havent had a good day to inspect.

But another update I was driving a little bit of a longer drive and hit an uphill stretch for 1 mile and my temp guage started to raise and I got a video of it. At the end of the video you see I let of the throttle and it goes back to 190. https://photos.app.goo.gl/1iq8swfwYaCEE2Ka9

Then on the way back I was going around 75-80 the entire time and the temp guage stayed right around 210-220 for the whole drive back. Does this video help at all for diagnosis?

 

Unfortunately I do not know if this is the case for the SAI Pump. I have had this code since we got the car 3 years ago and it has not seemed to affect performance. However since it always has the code who knows what im missing out on.

On another note I have looked into this some more and noticed that the expanison tank is starting to leak. After a drive you hear it hissing and leaking out of it. watch this video and turn audio up. https://photos.app.goo.gl/XcxgbvVctTeiEJ7c7

I just ordered a replacement for this and i will try to install today and report back. Could a leak like this cause coolant temp to raise as well?

Thanks yall!

 

I'm having this exact same problem.
Low coolant warning and what looked like a leaking expansion tank. Bought new one but leak was actually coming from small return hose at top of tank. Replaced hose clamp, no more leak. However this did not fix the temp rising problem. I think this is a symptom not a cause. It never seems to go over around 220 but until a few month ago it never passed 190.
I checked my hoses as suggested by PZ above the lower hose is definitely cooler than the top hose, not cold but just warm. The thermostat is not old but Im going to replace anyway before radiator simply cause its so cheap.
Another thing too is my problem seemed to happen shortly after replacing o2 sensor. NO cel light so probably not fuel trims.

As for your SAI it probably a disconnected hose to the pump. I had this for a year before looking into it for inspection. Reconnected hose, added couple clamps, light went off. I saw absolutely no difference in anything except MAYBE gas mileage.

 

Given that it’s the 1.8, I would suspect the water pump. Possibly a bad impeller.

 

"I just ordered a replacement for this and i will try to install today and report back. Could a leak like this cause coolant temp to raise as well?"

Pretty sure most here would agree with this statement...."ANYTHING that allows pressure to escape, will allow the temperature to increase".

GrGr mentioned something about "replacing the thermostat because it's so cheap".....might wish to look into that process.....get the kit.

 

Changed thermostat even though old one was only a few years old and temp now stays at 190. Drove it all day, even on hills where the temp would always climb it stayed at 190.
The lower hose still doesn't really hot like the top one. It just gets really warm and takes a long time to get warm. Not sure if this is normal or not. Most other cars I've owned both hoses get really hot after thermostat opens.

How Hot is the lower hose supposed to get? As hot as top?
Both heater hoses get really hot and I did put a metal impeller water pump in about 3 years ago.

Not sure if this has anything to do with this but i also changed the oil pressure switch and harness. Occasional oil pressure warning, bought switch, went to remove and sensor connector was broken, wire was just hanging on the pin. So I changed switch anyway. Another case where I should have looked before buying parts.

 

Good to hear yours was thermostat as well grgr. I replaced the coolant tank as it was doing the same thing as your but it still happened. I replaced the thermostat here this last weekend and so far 2 drives to work over a moutain and back and guage stayed at 190 the whole time. So it looks like it was the thermostat. I checked when I had the thermostat out if the water pump impeller was broken but its a metal impeller and working well. Well see how it drives the rest of the week but looking good so far. Thx for the help All