BMW E36 Six Cylinder Thermostat Replacement
Thermostat replacement is a critical part of maintenance on a BMW especially for E36 owners. This is because the coolant system is at risk of failure after every 80,000 miles. Typically when I work on an E36 coolant system I do an entire overhaul. This means that I’ll replace the water pump, thermostat, upper and lower radiator hose, and potentially the fan clutch. However, if you’re only having symptoms of a bad thermostat or you don’t want to get into a big coolant system overhaul, it’s quite simple to replace the thermostat.
Thermostats can fail in the open or closed position. A closed position failure is much more dangerous than a failure in the open position.
If a thermostat fails in the closed position the vehicle can’t be driven until the thermostat is replaced, it will overheat very quickly otherwise.
If a thermostat fails in the open position the vehicle can be driven, however replacement should be made as soon as possible. I have friends with classic cars that intentionally remove the thermostat so they never have to worry about it failing!
The typical symptom of a stuck open thermostat is that the vehicle has difficulty heating up to optimal temperature. Typically your thermostat needle will heat up to the middle well within ten minutes, however if the thermostat is stuck open this will take a considerably longer period of time. Another common symptom is that you have no heat, air should still blow through the vents but it isn’t hot.
Because of the potential serious engine damage sustained if an e36 overheats, most experienced e36 owners recommend regular preventive replacement of the coolant system.
Another thing to remember is that coolant system rebuilds are different if you have a four cylinder e36. If you have a four cylinder you can perform a thermostat replacement in under 30 minutes. If you have a six cylinder you will need to remove a few things to gain access to the thermostat.
Because inline-six cylinder thermostat replacements require more parts to be removed I will focus the DIY on the six cylinder.
- Put the front of the car on jack stands/ramps, this will help with access to the radiator drain plug, and with bleeding the air out at the end of the thermostat replacement.
- Drain the coolant system, for this job I drain it from the radiator and leave it at that. There is a blue flathead drain plug at the bottom of the radiator. Unscrew it and it will pour out coolant, otherwise when you disconnect the upper radiator hose it will pour out coolant.
- Remove the fan clutch in order to gain more access to the thermostat. To remove the fan clutch I use the fan clutch removal tool that I ordered off of ebay. It’s a $15 wrench and tool that latches on to the bolts to prevent it from spinning. Remember that the fan clutch is reverse threaded!
- Optionally you can also remove the fan shroud to gain more access to the thermostat (Definitely don’t have to).
- Remove the Serpentine belts, you have to remove the AC belt first. Both have tensioners with 15 mm bolts on them, simply turn to release the tension. The AC belt tensioner is located at the bottom passenger side of the vehicle and is most easily accessed from underneath.
- Disconnect the upper and lower radiator hoses from the thermostat. Don’t disconnect the hoses from the radiator unless you want to replace them.
- There are three 10 mm bolts that hold in the thermostat housing to the block. The top bolt is very easily accessible, however the bottom two are a little more difficult to spot.
- You also need to loosen a 13 mm bolt that holds in a fastener above the thermostat housing. The fastener will prevent you from removing the housing, so you must loosen the fastener bolt first.
- Remove the housing from the block, the thermostat should remain in the block. You can also take a look at the thermostat and you should see a small arrow on the thermostat, it should be pointing up.
- The thermostat may be really stuck in the block, if this is the case just make sure you do not pry on the block with a screw driver. Typically, a little tug on the thermostat will pull it from the block.
Reassembly for the most part is pretty straight forward.
- Make sure to clean the mating surface of the block if there is any old RTV/Gasket material.
- Don’t forget to install the new O-Ring on the thermostat, and install the thermostat with the arrow facing straight up, this is very important.
- The plastic thermostat housing doesn’t require gasket maker, however the aluminum housing does need a very thin layer of RTV sealant.
- Re-install the housing, hoses, and fan. Remember to start off the thermostat bolts by hand as they are easy to cross thread. When tightening down the radiator hoses remember not to tighten to much as the clamps can crack the thermostat housing.
- Prior to taking a test drive make sure to bleed out the system and fill the coolant.
The Fan Clutch Removal Tool is an absolute must have for DIY BMW owners as removing the fan clutch is a common step in many DIY’s.
If you’re replacing the thermostat housing, swap the plastic with an aluminum housing unit.
This is a really good time to examine the serpentine belts for cracks, and replace if necessary.
The thermostat needle on an E36 is set by the DME and NOT a direct indication of how hot the engine is! If you just wait to shut off the engine until the car reaches the red zone your engine may very well have already suffered damage! At that point the best thing to do is pray…