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2004 1.8T running hot

18K views 95 replies 11 participants last post by  scotts13 
#1 ·
Hi all,
I have a 2004 Passat w/1.8T. Last Thursday I noticed coolant leaking from the front of the engine. Once home I was able to remove the timing belt covers to reveal the water pump leaking. After changing the water pump, I refilled the coolant but did not know of the bleed hole method at the heater core. I was able to restore the fluid I'd drained out to swap the water pump so I figured I was good to go. BTW, I ran the engine after I had filled the reservoir a couple of times and squeezed the hoses to get as much air out as I could. Anyway, test drove it a couple of miles with no issues. Needle on dash indicated 190 as it always had. Ran the car for two days with no leaks, issues, etc. Then on Monday while in stop and go traffic I heard a bubbling sound and noticed the dash gage climbing past 190. Pulled over and shut off the engine. When I checked the coolant reservoir, it was below minimum as some had boiled over. Had the car towed home where I filled the coolant reservoir and started it up to see if it would boil over again. It didn't. I then hooked up my OBD reader to see what temp the coolant was running at. It was right around 205 for about 20 minutes with the car idling. Took it for a test drive on the highway and the temp slowly rose to around 215 and stayed for about 5 or 6 miles. When I came to an exit ramp it rose slowly to 228. At this point I was thinking the thermostat was ticking so I changed it with a vw thermostat (189 degree). Refilled the coolant system using the heater core bleed hole method and went for another ride. The car still will creep up to 230 and showed evidence of coolant being released by the cap. Now thinking the head gasket was blown I tested for exhaust gases in the coolant. No exhaust gases were present after running the engine at around 205 degrees for 10 minutes. What's the normal operating temp of these 1.8's. I now realize the dash gage is absolutely worthless as it's programmed to stop at 190 for a huge range of actual temp according to my OBD reader. The only other issue with the car is a code for lean idle mix. I found one of the preshaped rubber hose elbows torn coming from one of the steel lines off the turbo feeding back along the passenger side of the engine. Not sure what it is. (maybe EGR function?) Any ideas on why it's running hot? Sorry for the length of post. I just wanted to make sure I left nothing out which might help with the troubleshooting. Thanks for any light that can be shed on this.
 
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#37 ·
gigi123, Understood. But on the same level, when the guy is holding a $60 part that's identical to the $25 part it's tough to say one is different from the other. Especially when they depict the OEM image with no other qualifying statements on their online advertisement. I've seen parts in the past which state the image is representative. If ELTH made two identical parts for different customers, but left the part marking off their non-VW/Audi client, I would expect to see a dark blue switch identical to the part marked version minus the markings. In this instance, the $60 part was identical in color and shape with the $25 part. In other words, does the emperor have beautiful clothes... Their function might be the same, I just don't like the bait-and-switch tactic. Very misleading.
 
#39 ·
No problem. As it turns out I went to ECS online and ordered a switch only to find out it doesn't ship for two days. Unfortunately I paid for overnight with my order. This morning I found a dealership that has the part on the shelf for $54 so I cancelled the ECS order and will pick up the part at noon today. By tonight I should be able to verify the cooling system operating to proper parameters. Let's hope. Thanks again for the clarifying description on the sensor/switch ends. Kind of removed all doubt. :thumbup:
 
#41 ·
Just got home. OBD says 231 and no fan. Once again coolant dripping from overflow pipe. Can someone explain why the CTS would operate the fan on a single speed but the fan switch doesn't turn it on at all? Is there something else I should be checking? How reliable are the OEM fan switches?
 
#42 ·
tomvw, I just put the old blue switch in a pan with water and heated it to boiling and checked the contacts. At room temp, open on all pins. At boiling, pins #1 & #2 close to .2 ohms. pins #3 & #4 read around 16 Mohms. Pins 1&2 are on the square side of the plug. Yet when that switch was in the lower hose the fan didn't work at any temp. I'm assuming the two pins (1&2) are the low speed pins. Now I'm back to square one. Car boils over, fan never comes on.
 
#43 ·
Yet when that switch was in the lower hose the fan didn't work at any temp. I'm assuming the two pins (1&2) are the low speed pins. Now I'm back to square one. Car boils over, fan never comes on.
This means that the lower hose never gets to the boiling temperature. Now you just need to find out why:banghead:

Or the circuit is bad or the fan is bad. Did you try shorting the 1&2 pins to see if the fan comes ON?
 
#46 · (Edited)
I am not going to try to explain to you why switches and sensors behave the way they do, just accept that they do.
As I have already said, it appears there was and is nothing wrong with the fan thermal switch.
It is probably just coincidence that this was noticed after the repairs.
Forget about all that and concentrate on trying to solve the problem or get someone else to do the job.

If the fan does not run while the engine and AC are running, there is an electrical fault, one of the 3 relays or one of the sensors, wiring, etc.

The low speed relay or fuse are the most likely. (the fuse is on the relay plate)

Does the AC compressor run ?
When the CTS was in place of the fan thermal switch, did the fan run at low or high speed ?
 
#47 ·
I would like to contribute to the conversation, but it seems that you're ignoring the problem of why the engine is getting hot. I am finding, now that my overheating problem has been fixed, that my aux fan almost never runs (although it's been relatively cool here lately). I think I would still recommend one more time that you change out the thermostat just to be sure it's not faulty. Are you sure you installed it in the correct position (I know, dumb question but I had to ask). Lets find out why the car is getting hotter than normal.
 
#48 ·
This post is getting a little confusing... If I understand fallon's problem correctly (l sometimes read long posts very fast and skip some parts :)) the problem is no longer that the car overheats, or rather that the fan (electric) won't turn ON, and obviously after some standing/idling time, the engine will boil over (we can call that overheating). is this correct? The electric fan DOES come on with the AC on, correct? Does the engine behaves (overheats) the same if the AC is ON (hence the fan is ON)?
Personally I don't think the CTS at the back of the head controls the fan, but I could be wrong (or maybe this has never been said and I misunderstood).
Can you shed some light on this, fallon?
 
#49 ·
gigi123, If you read all my posts, then you'd see that the fan only ran with the a/c on and engine running before I change the lower radiator hose switch. When I erroneously put a temp sensor/sender in the lower hose, the fan would come on around 170 (according to the OBD reader) and stay on thereafter while the engine was running. It only ran at one speed as I never discerned a higher speed no matter what temp the engine was at. Now that I've put an OEM fan switch back in I'm back to square one with the fan not coming on at all except if I turn on the a/c. The a/c compressor runs but the system needs a charge. Without the a/c on the engine runs between 205 and 215 on the highway. Around town, stop and go, idling in the driveway for 7-10 minutes after I get back it will creep up to 230 (coolant will release from reservoir at this point). With a/c on, running around town, stop and go, idling for 7-10 minutes after I get back it'll rise to around 221-226 but not release coolant. The reason I was asking the difference between the CTS and the fan switch as far as pin functions is that when I tested the old fan switch (blue OEM style) in hot water, pins #1&2 went to 0.2 ohms (closed) and 3&4 were at 16 Mohms. I was wondering what pins are active in the CTS which would cause the fan to come on at all. If pins 3&4 closed on the CTS it might give an indication on which circuit is actually giving me a problem. That's why I was questioning relays. I've tested the coolant system for exhaust gases when it's been around 226 in an effort to rule out a head gasket leaking into the coolant system. That was negative so I'm stuck with the electrical side of the equation. If a relay controls the two speeds, that would be something to check, if the switch itself controls the two speeds, then jumpering the two sets of pins might show that. I guess my next step is to heat up the CTS sender and see which pins do what and go from there. When I changed the thermostat, coolant in the reservoir became warm around 190 (according to the OBD) so I'm assuming the thermostat is working as it should. Judging from the residue that was on the fan switch I removed, I'm sure a good flushing is in order. I just want to see the fan running as it should. When you said, "This means that the lower hose never gets to the boiling temperature." I'm sure it is getting to boiling temp hence the reservoir coolant release. I'm thinking a wiring diagram might help for the further troubleshooting I'm no doubt in for. This is just another "black box" for me to work through.
 
#51 ·
Fallon, there is a possibility that your expansion tank cap is the only problem, like tom suggested. However, usually in a cooling system (Passat b5 included) the fans should come on before boiling point, even with no pressure in the system. In case we need to explain this what Tom is suggesting (I hope) is that your system would not boil if your cap would be able to keep the pressure in the system (pressure and boiling temperature are proportional).
HOWEVER, if the coolant in the system/sensor reaches 230F (110C) the fan should come on, regardless of pressure, boiling or not. I think this is what we need to investigate. First, it's very possible that your CTS (the one that reports the coolant temp, on the back of the head) reads a little high. My guess is that this is not the cause of your problem, since you get the coolant to boil... Then you might have a circulation problem: coolant at the bottom hose is cool enough to not trigger the fan, the switch doesn't see 230F temperature.
Then, you could have an electrical problem but this you can eliminate by following Tom's advice. If this would be my project, I would start with checking the fan (or as Tom said, wasting my time).
I can't think of any other reason why you would have this behavior, since you tested the switch and you confirmed that on boiling water (100C) it works.
 
#53 ·
fallon, only one fault symptom has been identified, losing coolant. The fan is working at least on low speed.
This has become too confusing with everyone approaching it from different angles, if you would like further help from me send me a PM.


NOTE: If the coolant is boiling in the head due to low pressure and/or incorrect coolant mix, head damage is likely to occur.
 
#54 ·
fallon, only one fault symptom has been identified, losing coolant. The fan is working at least on low speed.
This has become too confusing with everyone approaching it from different angles, if you would like further help from me send me a PM.
Let me try my Tom impersonation: Tom if you don't agree with approaching it from different angles you shouldn't join a forum with more than one member! If you would have bothered reading the summary of the 2 pages of posts with the problem as fallon sees it, you would see that he is concerned with losing coolant as the effect of boiling over. He might not lose coolant under normal conditions, and for sure this is not what concerns him at this point.
How am I doing?
 
#57 ·
Ok first off, Tomvw - I'm sorry if this thread has become such a sore spot for you. I see you post on many other threads and my objective here was not to overburden you with my problem. I'm definitely not sitting home thinking of ways to torque you or anyone else for that matter. This isn't the only thing I have going on in my life at the moment. My wife of 27 years is losing the use of her right arm due to an injury suffered in a rear end collision. If that isn't bad enough, she was just diagnosed with stage 4 cancer. My youngest of 6 children has Down Syndrome and just finished 2 months of a respiratory infection requiring 24/7 monitoring of his oxygen stats. Chest PT around the clock as req'd (administered by me). When you say, "...or get someone else to do the job.", there is no money to pay for that. I have to make apple pie out of horse sh*t to make ends meet. I do the best I can with what I have. The learning curve on this car is no different than the string of Saturns my kids went through. I try to report the symptoms as best I can as I see them. I still have no idea what "normal" operating parameters are for this car. You see things differently as you've spent more time with these than I have. Not many people I know come to these sites just to pester other posters. I'm stating all this in the hope you'll see that everyone walks a different path. Everyone has outside influences that can hinder their decision making processes. You might not have a lot of other distractions, others aren't so fortunate. That being said, everyone who's taken the time to post on this thread I'm grateful to because they've given different insights I might not have learned otherwise. Try not to shoot at others if their opinion differs from yours. Everyone's trying to help. If you don't want to post anymore, fine. Thanks for the help you've given so far. I really do appreciate it. I found some components to hobble a pressure tester for the coolant system and will be posting back with the results.
 
#58 ·
Ok, so I hooked up a tire pressure tester to the coolant tank and started the car. 20 minutes in the pressure rose to 6-8 psi at 190 on the OBD. Another 15 minutes and the pressure is at 0. The OBD reads 215. Another 10 minutes or so the temp's at 231 with coolant dripping at the bottom of the tank. I used an inspection mirror to verify it was coming from the overflow spout only to find a small crack in the tank (just replaced in October) right next to the overflow spout. There was also drops coming from the overflow spout but the system pressure was still 0. I removed the cap slowly to find a crack in the filler neck that extended below the metal sealing ring in the throat. That explains the dripping at 0 pressure and 230+ degrees. Went to Autozone to pick up a tank they had in stock. Replaced tank, started car and took for a test drive with pressure gage installed. System pressure was at 12 psi and temp read 215 with no electric fan. Came home let idle up to 235, no electric fan and no dripping from overflow. So with the system now holding pressure (around 15 psi at this point), 235 doesn't lead to coolant loss. I still don't see why the electric fan doesn't kick on though. Anyway, decided to charge a/c while everything was running and a/c fan came on as expected. While charging the a/c I heard for the first time the second speed of the fan. After a/c system was charged, let it idle for a few minutes. Temp was at 226 with no fan (a/c shut off at this point). Found a curved hose and replaced the sheared one on the side of the engine. Maybe that'll clear the P0171 code now. So at this point, coolant system holding pressure, reaching 235+ doesn't engage the electric fan. I guess the last step is to get everything up to temp and check to see if the #1&2 pins on the fan switch are at 0 ohms.
 
#60 ·
I read your sad post, and am sorry that I can't do anything to help you with those problems.

I'm sorry if this thread has become such a sore spot for you. I see you post on many other threads and my objective here was not to overburden you with my problem.
This was not the case, I just got tired of fools posting contrary to what I posted, and you following their incorrect information.
I found I was just wasting my time and effort. I like to help but eventually get tired of banging my head against the wall.
This could have been fixed long ago if it hadn't been for fools posting rubbish. I posted the answers to your problem in post #20.
Although it doesn't seem to be recognized on this site, in real life I am well known for extreme patience.

gigi123 is at it again, and he should know better. Your cooling system is fine now, the fan should NOT be on under the conditions you described.

This is definitely the last help that I will give on this thread, but I am still happy to help you via PMs, my patience is almost endless.
 
#61 ·
gigi123 is at it again, and he should know better. Your cooling system is fine now, the fan should NOT be on under the conditions you described.
I am not sure what Tom means, but I know he is wrong about the system being fine. Cooling fan SHOULD come ON before coolant hits 230F. Keeping pressure inside and therefore not boiling over is just a band aid. You can't see the blood anymore but it's still bleeding... All cooling systems are designed to keep the coolant temperature BELOW boiling point at atmospheric pressure. So yes, I know better :)
 
#62 · (Edited)
Accidentally posted in the wrong thread.

While I'm here, gigi123 of course you are not sure of what I mean, because you have no understanding of how the cooling system works.
230F checked where the coolant leaves the head and reported to the gauge and ECU will not cause the fan to run.
The Fan Thermal Switch will only bring the fan on (low speed) if the coolant is above 197F after passing through the radiator.

This cooling system is now only showing signs of normal operation.
 
#63 ·
Cars in Australia must behave different because all the cars in the rest of the world will have the lower temp radiator hose (at the temperature where thermostat is fully open) at the same temperature as the head coolant. It's due to a magical device called water pump that circulates coolant all over the place. There is no way a car with 230F coolant temperature will not turn on the fan assuming all is good. I think you would agree if your mind can move past the "I'm right and you are wrong" attitude.
 
#64 ·
So I'm heading to lunch today running the a/c as it's 85 out today and everything seems to be fine. I tracked the temps for the last two days with the OBD reader and had the same 235 show up at various times while idling. No boil over, no coolant leaks anywhere. That being said I left the OBD home today figuring everything seems to be fine. As I'm nearing McD's I notice the air smells stale. Then I realize for whatever reason the a/c is not cooling. Figuring I sprung an a/c leak, I left the a/c on as the low pressure switch will protect the pump but I wanted to keep the cooling fan on. As I get to the ordering spot in the drive thru I notice the temp gage on the dash starting to climb (of course! I'm in the f***ing line with no where to go). I turn the heat on full blast just as the gage is just below the red. By the time I get to the pay window (two cars later) the needle is coming down and is halfway to 190 from 260. By the time I get to the pick up window I'm back to 190. And of course no OBD to verify what the head temp is. Once out of the line, I opened the hood and shut off the a/c to see if the fan would kick on. It didn't. With the gage at 190 I have no idea what the real temp is. There was no indication of coolant leaving the reservoir as everything looked dry. Reservoir level unchanged. So I've changed the water pump, thermostat (OEM), fan switch, coolant reservoir, and timing belt hydraulic tensioner. Could this be the CTS breaking down? It really sucks I didn't have the OBD to verify what temp was being indicated. I guess I'm not out of the woods quite yet.
 
#65 ·
Fallon, please for the love of god, replace the thermostat again. Check it's orientation, make sure it's installed in the correct direction. I had identical symptoms to yours and now with a new thermostat I am back to normal operation and my temps never get above 218* (as reported via the OBD connection). I believe the AC has some sort of circuit to stop the AC from cooling if the coolant temps are above a certain temperature. I too experienced the same thing- when the car started to get hot my AC stopped working and once the engine returned to normal operating temps the AC started working again.

Don't worry about the fan so much. It's not why your engine is hot.
 
#67 ·
tcervinsky, there are a few small differences between fallon and your problem... His car ALWAYS overheats when is idling. Yours will overheat when putting high load on the engine, while driving. I am not saying that I know what is wrong, just for the sake of being accurate... I guess he can replace the thermostat just to be on the safe side (cheap repair).
Fallon, I would suggest to run the electric fan all the time (just short pins 1&2) and use your OBD reader to check temperature all the time. Idle, driving slow, driving fast etc. Post back and we'll see what is the next step. Since today you had AC on and still overheated, I assume it's not a safe bet it won't overheat but we'll see.
 
#69 ·
Actually in the final days before I made my repairs the car did begin to over heat while idling. By then I was controlling the temp by increasing the RPMs and running the heater on high (the daily outside temps where barely 50* F so running heat didn't bother me much).

As I understand it the AUX fan should only come on if there is a condition that causes the engine to be excessively hot (or the AC is turned on). IMO focusing on when the fan turns on is ignoring the fact that it shouldn't be turning on at all under these conditions. I've posted my temperature reading (via OBD) under normal use and load, 218*F tops. Can anyone else confirm that is what they see too?
 
#72 ·
Drove in this morning this morning monitoring temps and never got above 215 for the drive in. At idle in the parking lot it creep to 221 and stay there. If the a/c shuts off when the engine gets too hot and the engine temps reported to the ECU come from the CTS on the back of the engine, could this be the CTS breaking down? Yesterday's episode in the drive thru got me thinking. The gage on the dash was going up but when I turned on the heat full blast it cooled down before I was even out of the line. That seemed a little quick to me. If the system had truly gotten that hot, wouldn't the cap have released coolant? I would think the pressure would have exceeded the 15 lbs yet everything was dry under the hood. Do CTS's start throwing intermittent high temp indications before they fail? Between a complete coolant system flush (note residue found on old fan switch in earlier post) and the CTS there's not much else I can think of that's triggering this condition.

tc - the thermostat was installed correctly (spring inside, bullet facing hose). Do OEM stats fail out of the box? The fact that the engine seems to run at normal temps the majority of the time tells me the stat is working as it should. If it was backwards or stuck, wouldn't the engine overheat all the time?
 
#73 ·
Fallon, the dash gauge is not linear. It stays in the middle for a pretty wide temperature and then it "jumps" to red when the temperature exceeds a certain limit. What happened in the drive through: the temp exceeded the upper limit, AC turned OFF, gauge started peaking up. Then the heater core cooled the temp a little, hence the gauge goes down. A good system holding good pressure would not release the pressure under these conditions, it would release if you let it climb more but IMO not before it hits (and stays) at red and you said it was right before red zone.
It's possible the CTS reports the wrong temperature, but I don't think this is your problem. Just a guess. Well, an educated guess due to the fact that the coolant will boil over if you don't build pressure. That is an indication that coolant gets hot... And if you have a mix of coolant and water, the boiling point is well above 100C (212F).
 
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