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Hybrid Touareg overheating

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SprinterX

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Discussion starter · #1 ·
I get random overheating, normally if after getting off the highway and then slow driving on side streets. But can randomly overheat anytime. The temp will rapidly climb to 280 but if I rev the engine a few times, it'll drop back down pretty fast to 200.

Replaced:
Thermostat
Mechanical Water pump
One of the (the easy one at the front of the engine) aux electric water pumps
One temp sensor (not the one under supercharger).

  • Suspected an air bubble but vacuumed twice.
  • The water level in coolant tank also fluctuates a lot: from too low, to nearly too full at times.
  • Sometimes the heater also doesn't blow hot air even with engine running. Other times it's fine
  • Windscreen defog also takes longer aometimes
I looked for the aux coolant pump relays but couldn't find them in the fuse box under the hood.

Any ideas? I'm lost...
 
Discussion starter · #2 ·
Is the HT circuit coolant pump the one under the the right hand side exhaust bank, beside the engine (PITA to change)? Reading this code:

14492
P192A00: Reserve coolant pump in the HT circuit, Dry running Status: Test failed, Test failed (current drive cycle), Pending, Confirmed, Test falled since last DTC clear
Status bits: 1
Priority: 2
Frequency: 254
Unlearning index: 255
Odometer: 224715 km
Date, time: 2024.01.24 14:06:45
Engine RPM: 1390 rom
Calculated engine load value: 79.22 % Vehicle speed: 52.195180147936 mph
Engine coolant temperature: 84 °C
Engine oil temperature: 26 °C
Barometric pressure: 14.5037738007 psi
Klemme 30 voltage: 14
Paramteric values: 20 96 28 12 8C 00 00 00 00 13 38 06 12
16 0A 67 10 10 00 00
 
#3 ·
Look at your coolant temp vs oil temp.... they get heated from the same block don't they?
I'd start looking at sensors to flush out any that are reading out of whack.... check all temp sensors that your engine has to see if what they read seems in line... maybe shoot the areas with a laser temp gun to validate the readings, etc.
I can't really explain that much of a difference between your oil and coolant temps....
 
Discussion starter · #4 ·
I also suspected a sensor mis-reading and decided to ignore the high temp gauge and not rev to being the temp down. Then it spewed a bunch coolant from the reservoir. I'm assuming a localized overheating/ boiling near a sensor that's picking up on it. Perhaps from low flow and/or heat soak.

I'm going to try replacing the second electric water pump. After that, I might test cooling this POS with a deep water crossing for TikTok.
 
#5 ·
So instead of reading (no cost) the 3 coolant sensors and the oil temp to compare, you'd rather load up the parts cannon?
Did you use the 3 bleeders on the various pipes to bleed the system as per FSM?
 
Discussion starter · #6 · (Edited)
Engine coolant temp sensor (B) goes high. Sensor A creeps up slowly. I'm assuming Sensor B is the one under the supercharger and in the cylinder head. If it was just a faulty sensor, the coolant wouldn't boil, overpressure the system and blow out the reservoir cap.

System was vacuum filled twice. Once by myself and once by the dealer ($$$). VW Sunnyvale tried to diagnose for a fee, had the car for 3 days and gave up and didn't charge me.
 
#7 ·
Without knowing where the high reading is coming from, you can't tell which sub system has the issue... Is it the high, the low or the electric?

If you think an electric pump has failed, it should be fairly easy to put a meter on that circuit to see if it's getting voltage, etc.
 
#10 ·
Figure out what sensor is what on whatever tool you're using.
You should have at least 3 coolant temp sensors that you can compare to block temp (oil temp).
You should probably log their readings to see if one jumps way out of whack compared to the rest of the system.
I asked about bleeding before... you ignored that..... did you use the bleeders?
If your diagnostic allows output tests, you should be able to cycle whatever pump\motor you think might be an issue to test its operation, etc. Check your electrical, using a meter, scope, whatever you have.....

Or fire the parts cannon.... but it won't be cheap
 
Discussion starter · #12 ·
Thanks for highlighting the bleed points. I'm sure the dealership flushed and refilled it correctly per the manual. I had done a vacuum refill but didn't bleed the two ports behind the supercharger. I just checked them now and no air came out and filled to the top with coolant.
 
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SprinterX
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