M52TU Coolant Temp Sensor Success

[TiagE39]

Just wanted to report to y'all about a successful strategy for a usually very frustrating job.

The coolant temp sensor went out on my M52TUB28 engined E39 (nonsense sensor data and a trouble code). The cluster temp gage was also occasionally reading full red when it wouldn't possibly make sense (e.g. cold start). The temp sensor (aka "dual temp sensor" in BMW speak) is located at the base of the intake port for Cyl No. 6 (closest the firewall), underneath the runners. This is an awkward spot due to the limited room between the intake manifold and the firewall, as well as the limited room underneath the intake runners. There is also a metal line that runs parallel to the runners but crosses the area where the sensor sits, further hampering access. Because of these restrictions, the default recommendation seems to be replacing the sensor when the intake is out for other work (e.g. heater lines, CCV, etc).

After doing some research on how to tackle this, some recommended using a 22mm O2 sensor socket in an offset or "crow's foot" style. A friend recently acquired a set of those for his own car, so I happened to have one available. Here's the exact kit.

I'm happy to report this worked exceedingly well. In order to make enough room, I removed the D/S microfilter box and the attached HVAC ducting. The O2 socket is small enough that it can slip over the metal line and mount onto the coolant sensor. Since there's a wire gap on the socket there's no need to remove the connector (which is good as the design isn't easy to detach without a small flathead screwdriver). I then attached three extensions (two 3" and one 6" both 3/8 drive, shorter ones on the socket end) which brings you about 1 or 2 inches above the top of the intake. It took about one firm 1/4 counterclockwise turn of the ratchet to break loose the sensor. I removed the sensor by hand. There's enough slack in the sensor lead that you can bring it to between the intake and firewall and visually use a flathead to pop off the connector.

Installation of the new sensor was basically the reverse, with two minor modifications. After threading in the new sensor by hand, the fit of the O2 socket was so that where the 3/8" extension plugs in was obscured by the intake and metal line. I switched to a 1/4" drive 12" wobble extension with appropriate size converters on either end. This gave me enough clearance to begin tightening down the sensor, but there's only enough room for about a 1/4 turn at a time. Plugging in the connector (purely by feel) was the last step.

Hope someone with a M52TU or M54 finds this useful!

[effduration]

Thanks for sharing... your method certainly works.

Another easy way is to take a cheap 22mm box end wrench and cut it in half to make a stubby 22m wrench. Attack from rear of engine underneath the intake manifold, where there is enough room. Use the open end on the coolant sensor and unscrew it..Usually doesn't take that much force.

[edjack]

Another moronic engineering idea to put the sensor in that location!

[jicaino]

Another moronic engineering idea to put the sensor in that location!

Actually it's a good idea that's not practical. But it's in the hottest spot.