Weird LCR overheating issue

[czaki]

Hi to all, I hope you can help me. I'm having a really weird overheating issue with my LCR.

The car recently started overheating when stationary. I'm running an aftermarket ECU so I checked the readings via USB for the CTS. It showed 110-115 degrees and the fans did not kick in. I started the AC as it must start the fans in low and high speeds depending on the temparature, it only started the high one and only for 5-10 seconds. After that it switched the fans off, then on again within 30 seconds. We tested fans and the slow speed was not present. At this point I thought the problem is fan related.

We have replaced larger the fan with a new one, tested them via the electrical connector of the thermoswitch and also for the fans, both speeds started for both fans. When the AC was turned on, it started the fans in low speeds, but still, the car was overheating without the AC running and the I only saw the low speed kicking in after reaching 105 degrees. So I assumed the thermoswitch is also faulty.

After replacing the thermoswitch to a new one, the situation remained the same, so we have checked the hoses going towards the thermostat and it was way colder then the other ones coming out from the engine. We started removing the thermostat and found out that it was stuck closed all the time (become faulty after one year, great quality, eh). Replaced with an OEM 80 degree one and hoped that our misery is coming to an end.

But with a working thermostat, a new and properly working thermoswitch and fan, the overheating issue is still present. At the very beginning we also replaced the fan control module with a working one, but the symptoms remained the same so we ruled the possibility that the module is faulty out. In addition, the fans only did not start with the AC off, with the AC on, everything is normal.

The CTS is the one which remained the same, and even at 110-115 degree, it's at the 90 mark on the dash, no overheating beep, nothing. With the stuck 87 degree thermostat in reached 90 in a few minutes and stayed there until I switched the car off. With the 80 degree thermostat the car is heating up a bit slower, but the gauge reading oscillates between ~87 and ~92 (only a small movement can be seen). But the figures on the dash did not show more than 90-92 even when the computer tells me that the engine is running around 110 degrees.

Any help would be appreciated. I really don't know what to try, maybe change the CTS. I really don't want to rely on the current behaviour of the car regarding the fans, I don't want to overheat the car in trafic during summer.

So, what's next in your opinion?

 

[traumapat]

If the dash gauge isn't rising above 90 I can't see theres a problem. The gauge is designed to sit at 90 unless certain parameters are breached, the temps your seeing are probably within those parameters.

Get her warmed up, then let her idle. leave it until the dash gauge goes above 90 and check fans are running. My guess is it wont go above 90 as the fans will kick in.

 

[czaki]

If the dash gauge isn't rising above 90 I can't see theres a problem. The gauge is designed to sit at 90 unless certain parameters are breached, the temps your seeing are probably within those parameters.

Get her warmed up, then let her idle. leave it until the dash gauge goes above 90 and check fans are running. My guess is it wont go above 90 as the fans will kick in.

Then why do I see high temps from the ECU? It uses the same sensors as the stock ECU.

If I let the car idle, the fans only kick in when the computer shows 105-110 degrees, while the dash says 90.

 

[czaki]

I've seen in other threads that you are asking whether the car is overheating at idle when sitting in traffic or only when pushing it.

Is that correct if the car overheats under heavy load, it indicates that the water pump is faulty? Then what's the case with the idle situation?

 

[traumapat]

Then why do I see high temps from the ECU? It uses the same sensors as the stock ECU.

If I let the car idle, the fans only kick in when the computer shows 105-110 degrees, while the dash says 90.

Because the dash gauge isn't giving a true reflection of temp. It won't start climbing until a certain real temp has been seen by the ecu.... in your case its 105-110.

If you stop the fans, you should see the dash gauge start rising.

You could get this confirmed with some of the decent tuners given your running a different ecu.

If the gauge did give a true reading it should be constantly fluctuating due to load, stat opening etc.

 

[traumapat]

I've seen in other threads that you are asking whether the car is overheating at idle when sitting in traffic or only when pushing it.

Is that correct if the car overheats under heavy load, it indicates that the water pump is faulty? Then what's the case with the idle situation?

Yes, WP if overheating under load, fans if at idle.

 

[czaki]

Because the dash gauge isn't giving a true reflection of temp. It won't start climbing until a certain real temp has been seen by the ecu.... in your case its 105-110.

If you stop the fans, you should see the dash gauge start rising.

You could get this confirmed with some of the decent tuners given your running a different ecu.

If the gauge did give a true reading it should be constantly fluctuating due to load, stat opening etc.

I see, my tuner uses the same sensors for reading as this is a plug and play ECU for our ME7.5.

Also the question is, why the needle is not climbing even around 110-115 degrees? When I had the slow speed problem with the old fan, the needle sat around 90 still when the ECU reading was 120 and got the car into engine protecting safe mode. That's why I can't really understand this.

Basically, If I would unplug the fans to prevent them kicking on, I won't see any difference on the dash, based on the above.

 

[czaki]

Yes, WP if overheating under load, fans if at idle.

Under load the car is around 95-98 when pushing hard, while only cruising is between 80-90 (as I have the OEM low temp thermostat).

By the way my water pump has been replaced since 35-40k miles. So this should be working properly.

 

[czaki]

Can airlocks cause this kind of problem?

 

[traumapat]

http://www.vwaudiforum.co.uk/forum/showthread.php/96923-Vag-com-engine-coolant-temp-reading


Post 6

You need to find out what the temp parameters are in your map. I don't understand why your car got to engine protect without the dash gauge moving?
But the difference between the ecu temp reading and the gauge is normal.

 

[czaki]

http://www.vwaudiforum.co.uk/forum/showthread.php/96923-Vag-com-engine-coolant-temp-reading


Post 6

You need to find out what the temp parameters are in your map. I don't understand why your car got to engine protect without the dash gauge moving?
But the difference between the ecu temp reading and the gauge is normal.

Thanks, I see now. But is there a possibility that a one-year-old CTS went bad and sending bad signals towards the ECU (referring to post #8) and good figures towards the AC display and the dash?

The boost in my map is limited by ECT values. So if the car is cold, even if I'm silly to floor it it won't make full boost as it is limited due to the values. Above 110 degrees I have a boost decrease around 1.0 bar, around degrees the maximum value for but is allowed to get only around 0.6 bars. In normal conditions my boost level is 1.4 bar.

 

[czaki]

As I have a custom ECU with custom mapping it is easier to check every value as I also have the controlling program for the ECU.

 

[traumapat]

Its possible I suppose but the CTS failures ive read about tend to create bad idle and cold running, often with a fault code.

 

[czaki]

Its possible I suppose but the CTS failures ive read about tend to create bad idle and cold running, often with a fault code.

No fault codes, it uses the same fault table as every other VAG car, the temp limit can be set individually.

I've replaced the CTS last spring along with the thermostat, the latter lasted for only one year. But I didn't suspected the CTS as the dash readings were 90, not less.

Not easy to be honest... Many thanks for your help!

 

[RobVT]

when you changed the thermostat did you check to see if the impeller is still attached to the water pump itself ?

 

[czaki]

when you changed the thermostat did you check to see if the impeller is still attached to the water pump itself ?

My friend helped in changing the thermostat, he didn't see anything problematic with the water pump. Besides the engine only gets overheated on idle, on cruising or flooring the temps are around 80-95 degrees.

 

[RobVT]

mine over heated the other week and the impeller come away from the waterpump shaft would only bite and cool itself down on idle

 

[czaki]

mine over heated the other week and the impeller come away from the waterpump shaft would only bite and cool itself down on idle

The opposite is happening to me. If I floor the car really hard, temps do not rise above 95+/-1 degrees. If I stop flooring the car it immediately starts to cool down. As I have an 80 degree thermostat temps settle around that number when cruising.

 

[Muttley]

CTS has two sensors in it, one feeds the dash gauge and a completely separate one feeds the ECU...

So what you see on the dash gauge has no connection with the reading that the ECU sees, and the ECU sensor can go faulty without any indication on the dash gauge.

The fans work off the temperature reading detected by the thermoswitch so if the hot water isn't getting to the radiator then the fans won't come on (and lets face it they wouldn't do any good anyway if the water isn't circulating).

fans kicking in at 105-110° is normally an indication that your low-speed resistors have burned out and the fans are only working at high speed - but you say you have new fans, and they work at low speed.

The thermoswitch is a simple passive device, one contact closes at 95° or so and the second at 105° or so. Is it possible that they are wired up the wrong way round (you would need to have mucked about with the wiring or have non-standard wiring for this to happen)...

Otherwise I'd suspect the fan control module.

 

[ibizacupra]

if there is a difference between the ecu temp and dash (logged) temp, then you have a sensor scaling issue in ecu, or sensor is faulty.

ecu scaling likely to be correct if it was working ok before

cts most likely at this point