TDI Temp Sensor
From Fozzee.net
Contents |
The Problem
A few weeks back, I was driving to Lincoln. It was pretty cold (maybe 20-25F) and I noticed that my temp gauge wasn't all the way to "hot" (190F). I figured that it was a combination of the cold, wind and highway speeds. The next day, I noticed that the gauge wasn't reading right even in town. All the while, the heater worked fine, I had plenty of coolant in the reservoir, and no other symptoms of cooling issues. I assumed that I had a gauge problem, as it wasn't running poorly. A quick check of the forums indicated that it's probably the coolant temp sensor, and that, at 100k+, it should be replaced first, before looking further.
The Tribulations
Through the pictures in the forum, I located the temp sensor (and knocked loose a glow plug connector, but that's another story) on the lower manifold, on the back (driver-side) of the engine. The boards had indicated that there were two sensors in use on the TDI, a "green" sensor (~$3), and a "blue" (~$25) sensor (so named for the color of the connector body). I couldn't determine for sure which sensor my engine took, so I headed down to the local O'Reilly (Auto Parts) to see what they thought. On the way to the parts place, my CEL/MIL came on (the glow plug issue). The guy indicated that the "green" sensor was the correct one, but that they'd have to order it for me (two business day lead, till the following Tuesday). $3 payable on pickup. Great.
Seeing my check-engine light, I ask if they had the scan-tool checked in that I could figure out what codes I was throwing. (At the time, I assumed that this had something to do with the temp sensor) The guy behind the counter indicated that their scanner "Didn't work on diesels". I was a bit too shocked (and in something of a hurry) to explain to him how my fuel source had nothing to do with my ECU's ability to conform to the OBDII standard.
The Resolution
So I finally got my sensor, and set out to replace it. I told Becky I'd be back in "an hour or 2"...
I had planned to do the "wet" process, that is swapping the sensor without draining the system. What I didn't know is that the sensor had shipped "unassembled" with the o-ring on the back, instead of the front hint, it goes on the metal part). After seeing a sensor removed, I was able to easily unplug the connector. I tried to squeeze the larger radiator hoses in a (misguided) attempt to pump some water back into the overflow, and out of the manifold containing the sensor. (it worked a bit)
I removed the clip that retains the sensor with a pair of bent-nose pliers. Lots of guys on the forums indicated that the clip was either difficult to remove or fragile in some way... I really didn't have any problems at all, it came out easily, grabbing it from the side.
With the clip removed, I figured it'd give the hose one last squeeze, and then try to make the swap. I had the sensor unboxed and waiting on the bench. Little did I know that squeezing the line would generate enough pressure to force the sensor out of it's socket... I lost quite a bit of coolant before I got my hand over the hole. The water was a bit warm, but not a problem. The sensor had fallen down behind the motor and I couldn't quite reach the one on the bench without moving my hand. So I moved my hand, grabbed the sensor (Assembled wrong, still, btw) and shoved it back in the hole.
I managed to locate the old sensor and realized that the o-ring was wrong. So I swapped the old sensor back into the hole (losing more coolant). I moved the o-ring and swapped them back (draining coolant for the last time). The clip went in easily, and plugging the connector back in posed no problem whatsoever (I was relieved, knowing for sure that I'd gotten the right color sensor).
I was glad that I'd picked up spare coolant, and at Becky's suggestion, used a plastic cup (With a line sharpie'd on the inside) to measure equal parts of water and coolant back inside. Lots of guys tout using distilled water, which I usually wouldn't worry about, but since I had a gallon on hand, I did. I used the compressor to blow some coolant off the tops of some of the plugs and stuff behind the engine, and backed it out to finish rinsing the top of the transmission off.
After a few scares with slow heating and temp gauge not moving (Who'd have thought that TDI's heated so slow, I'd never payed attention), the repair was a success. It didn't resolve my CEL (which I later discovered was glow plug related) but largely mission accomplished.
