How to Replace Thermostat and Temp Sensor DIY P0128 BMW M3 E90 E92 S65 V8
We recently had to replace the thermostat on an S65 V8 in the E92 M3. We took a few photos and thought we would share the basic procedure. Thermostats do not last forever and if you own an E90/92/93 M3 you’ll likely have to address it at some point. Various OBD-II engine management fault codes can indicate a potential thermostat failure. We were seeing a P0128 code which indicates; Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature). Since the vehicle has 135,000 miles on it, we decided to replace the thermostat as well as the coolant temp sensor.
The applicable Bentley Publishers repair manual (for your year/model BMW or MINI) will detail all of the OBD-II fault codes and code descriptions.
1) Remove engine air filter cover, by removing the Torx screws around perimeter and releasing the hose clamps on the intake air bellows to the plenum. Disconnect the secondary air inlet hose from bellows. Remove the bellows with the cover.
2) Remove the lower air filter housing.
3) Remove the cabin air filter cowl housing assembly.
4) Loosen the 8 hose clamps securing the intake plenum to the throttle bodies.
5) Release the harness plug from intake air temp sensor.
6) Pull plenum up and away from the throttle bodies (and the PCV oil separators on each valve cover). Release the hose at the underside rear driver side of the plenum, as well as the air tube at the front driver side of the plenum and pull plenum up at the front and out and away from the engine.
7) Remove coolant to prevent overflow when thermostat is removed. Use suction/vacuum device (such as syringe-style fluid transfer pump) to remove coolant from expansion tank or otherwise remove/drain coolant using the radiator drain.
8) Release the fuel line from the two securing clips at the thermostat housing and near the fuel rail.
9) Release the harness plug from the thermostat housing temp sensor.
10) Remove temp sensor.
11) Disconnect the expansion tank vent pipe from the top of thermostat housing.
12) Disconnect the main upper and lower radiator hoses from thermostat housing. Catch any coolant spillage with towels.
13) Remove the three thermostat housing securing bolts.
14) Pull the thermostat housing forward (under fuel pipe) to disconnect from the two pipe connections at the rear of the housing, then up and away from the engine.
15) Remove the thermostat from the thermostat housing.
16) Install new thermostat into thermostat housing.
17) Remove the two connector nipples from the aluminum coolant connectors (one or both of the nipples may have stuck with the thermostat housing. If so, remove the nipple(s) from the housing) and replace two o-rings on each nipple.
18) Lubricate the nipple o-rings with silicone grease and install the nipples into the coolant connectors.
19) Install the thermostat housing (and thermostat) onto the connector nipples and down into the thermostat mounting port.
20) Install and secure the three thermostat housing securing bolt.
21) Install the temp sender unit into the thermostat housing and connect the harness plug to the sender.
22) Connect the three coolant hoses (vent, upper & lower).
23) Fasten the fuel pipe into the plastic securing clips.
24) Install the plenum, connecting the rear air pipe and the front hose while positioning into the throttle bodies. Secure the throttle body hose clamps.
25) Connect intake air sensor plug
26) Install the air filter housing, air hose, filter, cover and bellows.