Thermostat Issues, A/C Issues, and "Logic" Questions

Hi all,

I've been reading through the threads on thermostat inssues, A/C issues, and cooling fan issues.

I have a 2003 TDi Jetta with about 207,000 miles on it. Thought I had replace the thermostat when I did the high mileage timing belt kit (ID parts) about 40,000 miles ago. When I reviewed the receipt for the repair it turns out I did not.

Here's what has been going on.

Over the last week the temperature was running just slightly high (1 tick past TDC on the temp gauge). I noticed that when it would run up there the A/C would cut out.

When I got home late one night I popped the hood to remind myself to double check all fluids the next morning. When I opened the hood I had what I thought was power steering fluid EVERYWHERE, so new problem.

Turns out my A/C compressor had fried and puked oil everywhere tinted green due to the R134A and dye I had in the system. Had the A/C compressor and power steering pump (also leaking) replaced. Antifreeze right where it is supposed to be, no soot or other contaminants in the bottle. Forgot to troubleshoot T-Stat (stupid I know).

Today I was driving home from work and noticed the A/C cutting out again and T-gauge running that same one tick high. Never during any of this did any lights SES or otherwise illuminate.

No milkyness to the oil.

Stopped at my uncles shop when I got it home and hooked it up to the computer. Coolant temp was 248 degrees. Sh!t. So, definitely ordering a new thermostat and Coolant temp sensor. Guessing mine is stuck partially closed...

So here are my questions...

1) Wahler T-Stat for $19 or OEM for $40

2) At what temp does the A/C cut out to cut load to the engine?

3) In testing my cooling fans both turned on when I turned on the A/C inside the car, however neither was running as it was sitting there idling with coolant temps at 248 degrees. That doesn't seem normal to me, is it?

Thanks in advance everyone.

Note to anyone reading this who questions whether the temp gauge is accurate... IT MOST DEFINITELY IS NOT! "mathematically I should have been somewhere around 217 degrees, not 248 based on the "gauge..."

I came across a VR6 the other day with very similar symptoms. It was over heating, and the fans were not running in low speed, but would kick up to high speed periodically.

I was thinking maybe the water pump was bad and not circulating the coolant to the radiator where the fan switch is (as opposed to the temperature sensor on the flange coming off the head) But now that I think about it, a thermostat stuck closed would have the same effect of keeping the fan switch in the radiator cooler than the rest of the system.

www.autohausaz.com has OEM Behr thermostats for $14. They have the tabs that lock into the housing and make installation much easier. 044121113 is the part number.

Check the readings of both your Instrument controller temperature reading, and your Engine controller temperature reading.

VW in its infinite wisdom has set up your dash temperature gauge so that it indicates dead center from about 167 to 225 F. So as soon as it wiggles above centerline you are above 225.

As mentioned above the radiator thermoswitch runs the fans, so the temperature 2/3 down the radiator must be hot enough to turn them on; engine coolant temperature has little to do with this. They rarely come on.
Bentley fan operating points:
low speed
on - 197-206 F (92-97 C)
off - 183-195 F (84-91 C)

Fast speed
on - 210-221 F (99-105 C)
off - 195 - 208 (91-98 C)

The temperature at which the ECU turns off the AC based on engine coolant temperature has never been clearly determined. Now we know it is 248F or lower.

Thanks folks. On a mini-vacation with the family camping so the Jetta is sitting safely at home in "time out" so to speak. Ordering up parts today so hopefully can fix quickly on Sunday before I have to be available to be on call Monday.

Love driving my truck but 20 MPG versus 46+ MPG, love don't cut it!

JP

fan switch should have kicked in high speed , unless you have air pockets in the radiator

checked the temp of lower radiator hose ?

Quick update for anyone that cares...

Replaced both the thermostat and the temperature sensor last night.

Good news is it appeared to solve the problem. Bad news is I have developed a pretty steady coolant leak. When I took apart the housing over the T-stat I saw that in a previous install the plastic fingers were in rough shape. Because I didn't plan for that I had no choice but to put it back together last night as I needed to have my car back today since 2 out of our 3 vehicles were "down for maintenance..."

Like I said, pretty steady leak and appears to be right behind the plastic housing so my guess is a) the housing is cracked, or b) I didn't get the o-ring or T-Stat seated perfectly in the opening. Wish I had smaller hands since it is in such a tight spot!

So time to order some more parts and get them coming...

Many people use a copper wire, ty-wrap, or string (something you can pull through the open end of the housing to remove) to keep the Tstat and oring in place while reassembling it if the fingers are broken (as they usually are.)