BHW operating temp + chronic air coolant loss + hydrocarbon test

96Brian

Well-known member
Joined
Apr 25, 2014
Location
Olympia, WA + Gold Beach, OR
TDI
2005 Passat GLS Wagon
Recently got VCDS and have been logging data to try to figure out chronic coolant loss. Does anyone know what typical operating temp is for BHW? with VCDS I see that the car gauge sticks at "190" from 85 c to 110c. Mine now typically ranges from 96 to 105 (except long grades - see below).
I have a chronic problem with coolant blowing out the overflow. Now with VCDS I see temps spiking going up hills and in some cases maxing to the red on the car gauge and up to 128c on VCDS; only under load, and on hills over 3/4 mile in length; temps retreat relatively quickly once hill is topped. This issue has increased in frequency since recent thermostat replacement. When I fill with coolant, I'm taking the steps outlined to get all the air out, but I believe somehow I am not getting all air out.
I've done several hydrocarbon tests - all negative, but I'm concerned that the test method is flawed - you have to open the system to attach the cylinder to draw gasses through - if it changes color, there's exhaust gasses; but....if you have to release pressure to do the test, what if there's only a compromised gasket and/or head at high heat/load?
We don't have emissions testing in my county, but the next one 25 miles away does - can their equipment detect coolant in exhaust gasses? If so, what do they need to look/test for?
I have a cheapo infrared sensor gun - anything I can look for in various temp differences on hoses or radiator to indicate source of blockage or problem?
Love the wagon, great performance, 39 to 40 mpg, delete done, only 129k miles but I'm growing tired of adding coolant and my wife refuses to take it on our trips to Oregon (400 mi ea way) due to the annoying "Stop Check Coolant" warnings.
I'd gladly offer a $100 gift certificate to the restaurant/pub of your choice in your town if any of the gurus out there can help me solve this vexing issue. I have data available - not sure what the best measuring blocks to trouble shoot would be - many have coolant temp, but there are so may other things.
Can't find a "trusted" shop near Olympia. Anyone up for a long distance consulting gig?
Brian
Olympia WA
Things one shop or another have replaced in last 20k miles
EGR cooler 15k miles ago
thermostat 2k miles
coolant flange 2k miles
Timing belt changed 8 k miles ago due to being oil soaked from crank seal leak and camshaft seal leak. Water pump not changed, was checked by tech, deemed good; was replaced 35k mile ago prior to my ownership, verified to be metal impeller (via Bora, supplier to trusted who did that job)
pressure testing, no issue apparent
heater core flush 30k miles ago.
 

vwztips

Veteran Member
Joined
Aug 30, 2009
Location
Greenville, SC
TDI
2005 Passat GLS Wagon TDI 5 spd manual w/BSM delete 2011 Tiguan TDI/DSG 2005 Audi A4 Avant 6MQ TDI 2011 BMW X5 35d
First was the T-stat a VW one? I have seen aftermarket ones not operate properly within the given range. (Normal temp ranges 90C to 93/94C)

Second was the water pump removed and checked to make sure impellor could not turn independent of the pulley?

Third, have you bypassed the EGR cooler temporarily?

Fourth, have you replaced the coolant bottle cap?

Fifth, any cracks in your coolant bottle?

Sixth, original radiator? Have you inspected both sides of the radiator for minor leaks?

Being that you are seeing elevated temps, I would start with replacing the T-stat and the coolant bottle cap.
 

DeliveryValve

Veteran Member
Joined
Mar 27, 2007
Location
Western US
TDI
Passat GLS Wagon
Did you pot boil test the thermostat before installing it? There have been new thermostats that fail right out of the box, so I never install one without verifying it works.
 
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