The CTS is at the back of the engine, did you replace that or the "coolant fan temp switch" at the front of the engine ?

 

I replaced the CTS.

The shop I took it to said the fans were running fine. When the gauge in the car is pegged the main mech fan is running, but 2nd or electric was not?

 

The thermostat could be having problems intermittently, or perhaps it's can't fully open to provide sufficient cooling for continuous speeds >65 mph.

Not sure if you're doing this, but don't turn off an overheating engine, but instead leave it idle with the heater blowing on max. Also, are you checking coolant level after the car has been sitting 4+ hours?

Finally, there's a dead band in the temp gauge at 190 degrees, i think either +-20 or +-40 degrees, so when the gauge does move above 190, it's a decent bump up.

Find a different shop as $750 is way too high to just swap out the thermostat. Might want to run a scan to see if there are any error codes stored.

 

Could be a faulty thermostat or water pump. Does it have any fault codes ?
Scan and post codes. A VCDS reading of the two temp sensors in the CTS could help.
If you have AC, does the electric fan run with engine running and AC on ?

 

if a CTS fails, it goes to zero. Never seen one fail and give a high reading.

If it is a thermostat, it is fairly cheap. 1 hour labor maybe and $20 for the part? Didn't take me long at all.

 

A CTS can fail in way that gives a high temp reading but it is rare.

I once had a tail light festoon bulb blow, you could test it with a meter and it read the same resistance as a new bulb.
Connect it to 12V and it would draw the same current as a new bulb, but did not produce any light. Strange but true.

 

its the waterpump. the impeller has broken away from the shaft but still manages to work at slower speeds. it is not the thermostat, CTS, or anything else.

time for a timing belt job, since you have to remove the belt to do the waterpump.

 

its the waterpump. the impeller has broken away from the shaft but still manages to work at slower speeds. it is not the thermostat, CTS, or anything else.

That is a guess based on the fact that the water pump often fails and causes these symptoms, and is probably right,
but with the information given, it could also be the thermostat, CTS circuit, blocked radiator core, or the electric fan.

 

Next time it shoots up jump out and feel the hoses lightly (or use an infrared temp gun to see what the motor temp is in several places). See if it is that hot. At 260 it should be boiling over or about to. If not then it is a faulty reading.

Are any other gauges doing weird things? MY first thought is that maybe a body ground is going bad and it is trying to ground out thru the temp gauge/sensor.

 

after some driveway testing here's what I came up with. I was measuring temp with an infrared thermometer where the top rubber radiator hose meets the steel tube going over the top of the motor. AC running on high electric fan was running.

2000 rpm 202 deg car temp gauge 190
2500 rpm 210-214 deg slightly over 190
3500 rpm 230 deg 255-260

after letting off the throttle going to idle, took roughly 15 sec to get back down to 190 on temp gauge and 200 on the steel radiator pipe. Water pump impeller???

 

Water pump impeller???

That would be my guess. Not 100%, but sure sounds like it.

 

Looking at those figures from the infrared thermometer it seems to support what the gauge is telling you. I would suspect the water pump impeller. It is building heat in the engine faster than the water can get it out above idle, The water will still flow without the pump, it just will be very poor flow.

 

spoke with VW dealer. they said it's impeller and needs timing belt also. $1250. I'll post when done what actual issues were.

 

kmwas, I'd check at least one other price before spending $1250 on a 1.8T timing belt job (the pump is a standard part of the job). I don't know how prices are in WI, but that's $250 - $300 more than around here, even at a VW dealer.

 

St.Paul MN VW dealer said close to $1500. depending on what else they'll find.

 

you might try an independent VW mechanic. you could save several hundred.

 

FWIW: standard book labor to replace the water pump is 5.7 hrs according to Alldata.

Local hourly rate x 5.7 hrs plus parts. Ecs has kits that include the water pump, timing belt, tensioner, fluid, & new thermostat. I am sure others do as well.

Volkswagen Passat B5 FWD 1.8T Engine Timing ES#8726 ECS Tuning Timing Belt Kit - Ultimate Plus - AWMTBKV2WAF