W12 Overheating slowly

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73blazer

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Last few days my Phaeton W12 2005 overheats unless I have the heater on full blast. Driving 50-70mph and 70-75F ambient outside, the dash temp creeps up. I logged Controller 1 group 1 coolant temp for an hour and half and it slowly slowly creeps up. Without the heater on it'll go to red pretty quickly.

Today I found some better measure blocks, Controller 1 group 130 shows radiator input temp (as engine output), rad output temp, and t-stat call duty cycle.

I guess I just want some eyes on this data or any other info someone might have. I'm pretty sure the water pump(s) are working otherwise it'd just overheat plain and clear and quickly and I wouldn't get much heat out the in cabin vents.
This Group 130 data (taken over about 40mins, 72F ambient outside, driving 55-70mph the whole time) shows the first t-stat call seems to have an effect on the output coolant but later, especially towards the end the input and output are diverging big time which somewhat says to me, that t-stat isn't actually opening at least when the engine gets nice and warm. Is that a fair diagnosis? I'm very new to VW vehicles so just want 2nd opinions, because that t-stat on this car is $300 plus 3-5hrs labor. (which is low for a Phaeton w12, easy job right!???)

 
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rhill2901

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If you already considered this, my apologies.


One of the top causes of an overheated engine may be worn, corroded, or malfunctioning parts. These parts include the head gasket, the radiator, radiator hose, and water pump. Other parts that may be worn and lead to overheating problems are the fan clutch, fan shroud, fan belts, and thermostat.
 
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Gremling

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Hi, Autoscan please.
(This is a verified user, so I assume it'll be OK to respond even no scan attached)?

* Check coolant reservoir correct level
* Could be bad/worn water/coolant pump, bad temp sensor, or combo of these.
* Check coolant reservoir for gas/bubbles, smell of exhaust, furthermore for discolourisation and/or oil film (head gasket).
* Check exhaust for excessive moisture (head gasket failure).
* Check Oil dip stick, is it fomy/white stuff on it, signs of water intrusion into oil circuit (head gasket)
* Use the Vagcom and check timing, incorrect timing can cause overheating (incorrect timing can be tell tale of stretched timing chain. Also could be worn guides/bad tensioners).
* Flush radiator (contaminations or residuals can case bad flow and heat transfer).
* Does the radiator fan start? Your car should have 2 front fans, one for engine coolant radiator, and one for the A/C system. Use Vagcom to activate engine coolant fan, if not running check voltage if no voltage could be fuse blown or failed wiring (could be fuse/wiring/defect fan)
* Bad or leaking injector can cause engine overheating (check each injector for spay pattern, lots of videos show principal of how to)
* Bad fuel pressure regulator could also cause this, but I would assume this would cause limp home or at least give error message, hence another reason for posting a scan.

Hope this helps you a bit on your way to fault find, please give feedback on your thread on final result for issue.

Regards
Gremling
 
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73blazer

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Hi, Autoscan please.
(This is a verified user, so I assume it'll be OK to respond even no scan attached)?

* Check coolant reservoir correct level
* Could be bad/worn water/coolant pump, bad temp sensor, or combo of these.
* Check coolant reservoir for gas/bubbles, smell of exhaust, furthermore for discolourisation and/or oil film (head gasket).
* Check exhaust for excessive moisture (head gasket failure).
* Check Oil dip stick, is it fomy/white stuff on it, signs of water intrusion into oil circuit (head gasket)
* Use the Vagcom and check timing, incorrect timing can cause overheating (incorrect timing can be tell tale of stretched timing chain. Also could be worn guides/bad tensioners).
* Flush radiator (contaminations or residuals can case bad flow and heat transfer).
* Does the radiator fan start? Your car should have 2 front fans, one for engine coolant radiator, and one for the A/C system. Use Vagcom to activate engine coolant fan, if not running check voltage if no voltage could be fuse blown or failed wiring (could be fuse/wiring/defect fan)
* Bad or leaking injector can cause engine overheating (check each injector for spay pattern, lots of videos show principal of how to)
* Bad fuel pressure regulator could also cause this, but I would assume this would cause limp home or at least give error message, hence another reason for posting a scan.

Hope this helps you a bit on your way to fault find, please give feedback on your thread on final result for issue.

Regards
Gremling
Well I didn't post a scan because there are no faults found. I did use my VCDS to produce the graph posted in the first post.

  • Coolant level is good
  • G62/63 temp sensors agree so I doubt it's those, and the fact that I can turn the heater on and get heat says coolant pumps are working, I would also suspect if no coolant flow it would simply overheat very quickly, not ever so slowly like this.
  • No sign of oil/exhaust in coolant
  • No sign of excessive moisture in exhaust
  • No sign of coolant in the oil
  • Timing....now what MVB are those, any idea?
  • I was planning on a coolant flush, on this car it's no small job, i bought it in February and have driven it 3000kmi, but this was very sudden, in my experience, radiators don't plug up overnight.
  • Rad fans are both working, although totally unnecessary while at any speed above 45mph (you move much more CFM through the rad at speed than a fan could ever hope to, the fan becomes the impediment at that point)
  • Leaking injector..that would require removal to check, 12 of them. I'd rather leave that for a last resort, plus economy and performance don't seem to be suffering in the least.

I'm still heavily leaning towards thermostat. The car's calling for it to open, and while in the beginning it seems to comply, towards the end it seems to me it's not. On this car it's a map controlled thermostat. it has some wax thing that the car can activate a heated thermocouple to open it, or it will open automatically at 110c. I'm guessing it's not opening much after it gets nice and warm.
 
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Gremling

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Agree with your inputs, seems like you are ending up with either pump og temp sensor. Radiators does not clog up over night, looking at the t-state cycle compared to radiator and engine output, it seems strange.

At end/bottom of this reply there are 4 relevant SSPs (VAG Self-Study-Programs), these few links to manuals for your car, but you probably have them already, but as you know, we all just want to help the best we can.

With respect to the speed for airflow thru engine, I do not believe your statement is completely accurate, as I understand this engine size is depending on fans to work and provide flow (if one or both fails in such a manner that it is recogniced by management system, indicator lamps lit and you would not be able to drive as per SSP250 pg 51,
"If a fan fails, the indicator lamp is activated and it is not possible to travel any further. This also applies if both fans fail".
see links below.

No leaks to other evidence of leaks or head gasket issues, so lets assume those are out of the equation.
The coolant valve may be acting up a bit, are you able to force it with Vagcom when engine is off, if so paying attention to the mechanical sound or lack of such.
How is the oil temp, have you monitored this?

Another question, you wrote that you had to use cabin heater for cooling engine, do you notice if the heat from here is very varm or just medium varm? Hotter engine (thereby coolant) should give off hotter air in cabin heat exchanger. If not hoter air then normal, it could be a sign of bad temp sensor (radiator temp sensor seems to be giving sensible readings) or air in system, but you have not mentioned that coolant system have been drained.

Below is a few links to manuals for your car, but you probably have them already, but as you know, we all just want to help the best we can.

I take it you have checked these:
http://www.volkspage.net/technik/ssp/ssp/SSP_270.pdf. page 35
http://www.volkspage.net/technik/ssp/ssp/SSP_248.pdf. page 45
http://www.volkspage.net/technik/ssp/ssp/SSP_250.pdf. page 8 and 9 and 46 onwards
http://www.volkspage.net/technik/ssp/ssp/SSP_222.pdf page 7 onwards


Hope this helps, looking forward to final verdict/solution.

Regards
Gremling
 
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Jack@European_Parts

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Sounds like a leak or flow issue to me, time to pressure test.

You can have a leak and it appear not present coming out in steam or on suction side resulting in no coolant evidence.
If the system is not entirely secure or flow is inadequate from faulty pump this can happen from spinning separated water impeller.

In addition to pumps, check flanges for damaged o-rings, sometimes a hidden o-ring on either bank can give up behind covers and at this age it is indeed possible.

Car of this age and rarity it might pay to disassemble and inspect everything and do a full x15 annual.

Check for FOD in coolant and conduits with isolated flow checks.
 
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73blazer

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Agree with your inputs, seems like you are ending up with either pump og temp sensor. Radiators does not clog up over night, looking at the t-state cycle compared to radiator and engine output, it seems strange.

At end/bottom of this reply there are 4 relevant SSPs (VAG Self-Study-Programs), these few links to manuals for your car, but you probably have them already, but as you know, we all just want to help the best we can.

With respect to the speed for airflow thru engine, I do not believe your statement is completely accurate, as I understand this engine size is depending on fans to work and provide flow (if one or both fails in such a manner that it is recogniced by management system, indicator lamps lit and you would not be able to drive as per SSP250 pg 51,
"If a fan fails, the indicator lamp is activated and it is not possible to travel any further. This also applies if both fans fail".
see links below.

No leaks to other evidence of leaks or head gasket issues, so lets assume those are out of the equation.
The coolant valve may be acting up a bit, are you able to force it with Vagcom when engine is off, if so paying attention to the mechanical sound or lack of such.
How is the oil temp, have you monitored this?

Another question, you wrote that you had to use cabin heater for cooling engine, do you notice if the heat from here is very varm or just medium varm? Hotter engine (thereby coolant) should give off hotter air in cabin heat exchanger. If not hoter air then normal, it could be a sign of bad temp sensor (radiator temp sensor seems to be giving sensible readings) or air in system, but you have not mentioned that coolant system have been drained.

Below is a few links to manuals for your car, but you probably have them already, but as you know, we all just want to help the best we can.

I take it you have checked these:
http://www.volkspage.net/technik/ssp/ssp/SSP_270.pdf. page 35
http://www.volkspage.net/technik/ssp/ssp/SSP_248.pdf. page 45
http://www.volkspage.net/technik/ssp/ssp/SSP_250.pdf. page 8 and 9 and 46 onwards
http://www.volkspage.net/technik/ssp/ssp/SSP_222.pdf page 7 onwards


Hope this helps, looking forward to final verdict/solution.

Regards
Gremling

No, I hadn't seen those and I was looking for the theory on how the two coolant pumps interact with each other. The SS250 page46+ explains exactly that! Very useful info here, thanks!

The heat from the heater when you turn it on to attempt to reduce or maintain coolant temp when it was rising, is extremely hot. The hottest heat you'd ever feel.
Oil temp goes to 240F very slowly and pretty much sticks there.
I don't have a completeservice history past 50kmi on this car, it now has 113kmi and I do not know if the coolant was ever drained. It was a job I was planning to do but being no easy job on this car I havn't done it yet. I did test it with my tester and checks out, it's level is right where it should and has remained the same the whole time be so I do not believe it's leaking, and I dipped a rag in and rang it out in a clear cup to get the color, while I'm a bit color blind, it appears to me to pink or very light red. So if someone did change the coolant they used the right stuff.It doesn't look overly cloudy or nasty.
 
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Jack@European_Parts

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Because it is a closed cooling system, you can indeed have an inward air leak.

Often people negate this factor and is usually a problem at o-rings & due to corrosion if not pumps or T stat.

A pressure test is a really good indicator fast.......
 
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73blazer

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Well thats one tool I don't have is any way to measure or pressure test the system by hand.
It's holding pressure as if I crack the cap when it's hot it's definitly got pressure. Even hours later after the car has shut off you can open the cap and hear a spit of air as if it's still has some pressure. Are there any poor mans way to pressure test it? I don't mind buy tools but I imagine the tool for this is Pheaton (or perhaps vw) specific as it needs to fit the coolant cap
 
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73blazer

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Well to be clear im not disputing a pressure test can provide input. But the fact that I've maintained 8 of my own and countless friends and families vehicles of various makes and models without that tool i perhaps hesitate to why i might need it now in life. But they're cheaper than i thought. Although finding one with the proper adapter to this system proves a bit challenging as most just say vw ornlist a few vw models non of which include the phaeton I'm. Not quite sure which one to buy.
But i still have a question. I've always relied on external.leaks or dropping coolant level as a means if your coolant system is not sealed....if as you say its an Internal leak' like from the outer to inner coolant loops as i read
...hows a pressure test gonna help? I'm not losing coolant as far as i can tell. How would a pressure test manifest a reading to an internal.leak?
 
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73blazer

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Hey i appreciate the input no matter how I sound.. So sorry if this sounds stupid. I've built engines and whole cars. But never done a coolant system pressure test. So i hook up the gauge and what am i looking for, a wavering gauge? Most system will.hold 14-20lbs. Id have to.look up the w12s value. My buddy has one he says he was a 'vw' adaptor. I'll have it tomorrow as he needs to return my tractor anyway. . I would assume.look.for hold of the system.pressure. What would indicate problems? Obviously not holding any pressure very low would. . Just wondering what the watch as she "warms up". And she will warm.up.
 
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73blazer

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I did that pressure check yesterday evening. 18lbs for hours, no loss. Not even a hint. And that's more than it should see. It was the "hose" hookup type so it was testing the cap at the same time.
 
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What about flow volume and tested under PSI?

What is physical status of T-stat when checked in boiling water or by heat gun or flame?
 
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73blazer

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What about flow volume and tested under PSI?

What is physical status of T-stat when checked in boiling water or by heat gun or flame?
Well that t-stat is buried under the intake, you'd have to remove it to check it. From the car's data as shown in the graph I posted, when it warms up it's being commanded to open, but there is no sensor on if it's actually open or not. I'm told their fairly common failure part on these W12's anyway and you can tell by the suffix of the part (AP) there have been many, many revisions over the years.
I'm not sure how to get a flow volume. We tested with it off. There's no way to really see or get at much of anything on this car's cooling system without disassembly of certain other systems that would render the car inoperable.
As I'm pretty sure it's the t-stat, and that's fairly simple to get at, I'm gonna go ahead and remove the intake and take the t-stat out.
 
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