Weird LCR overheating issue

[czaki]

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.

I didn't replace the CTS yet. It has been replaced, but as the thermostat showed me, aftermarket parts often won't last long... I bought a new CTS this afternoon, I'm going to fit it tomorrow. I hope it is going to cure my problem.

The fans are working if I test them through the connector, low and high speed as well. The thermoswitch has also been replaced, without any changes in the overheating issue.The connector can't be used wrong, it can only be applied one way, as it has a securing clip on one side. I didn't do anything with the fan wiring either, only disconnected the old and connected the new one after changing. I have standard wiring with a triangle connector, I didn't do the resistor mod either.

The fan control module has also been replaced for testing from a properly working car. That LCR had both fan speeds, the fans were kicking in when they should. We tried that module in my car before even changing the fan just to test, it produced the same symptoms as my car produces now. When we took this test module back to my friend's car, it continued working properly. That's how we ruled the module out.

 

[czaki]

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

The same ECU is used in a few cars here in Hungary with the same sensor scaling, only my car produced these symptoms so far.

The reading on the dash seems interesting sometimes. Yesterday the car heated itself up properly, overheated on idle, when flooring maxed around 95, cooled down to 80-90 (low temp thermostat) and when it waas stationary again, the dash showed 90 when the computer said the engine coolant temperature was rising to 110 degrees. I even saw 115 when the slow speed kicked in. Today instead, it was really hard to warm it up (although there was a 10 degree difference as yesterday was sunny, today was rainy) and to maintain the 80-90 degrees. The dash was showing 70 degree or less, I checked the AC display and it constantly said 90 degrees!

Will try the new CTS in tomorrow. What is the best way to prevent airlock? I assume air in the system won't help my case. IIRC our cars' are having a self bleed system?

 

[czaki]

Quick update: replaced the CTS this morning, refilled with coolant and got rid of all the bubbles in the system. The CTS shows better readings, the fans start in low speed around 104 degrees, switch of around 98 at idle. In traffic, no overheating at all. Gauge climbs to 90 and only moves around a little depending on engine conditions (1-2 mm movement maximum).

Perhaps there could be a temperature difference between the CTS and the thermoswitch that causes the fans to kick in late.

The funny things is that I "cooked" the old thermostat which was suspected to be faulty and it opened perfectly in boiling water and closed when it cooled down. I wonder why it didn't do such when it was in the engine...

 

[Muttley]

The thermoswitch reacts to the temperature of the water in the radiator, wheras the CTS is right next to the head. You would expect the temperature to be higher at the CTS.

Was the old thermostat installed properly and the right way round?

 

[czaki]

The thermoswitch reacts to the temperature of the water in the radiator, wheras the CTS is right next to the head. You would expect the temperature to be higher at the CTS.

Was the old thermostat installed properly and the right way round?

Yes, the thermostat was installed properly and worked properly for a few months. I don't know how it got stuck, but it opened perfectly in the kitchen.