When a coolant pump begins to fail, you’ll notice that the car tends to overheat at low engine speed, such as sitting at a stoplight. When you accelerate, the engine temperature will drop. Now, this is not always indicative of a coolant pump failure, but a good starting point. You may also want to try squeezing the top radiator hose with the engine warmed up and running. You should feel pressure build up on the back of the hose and surge once it is released. If you feel no pressure, it’s a fair bet that the coolant pump is failing. BMW updated E90 models with an electronic water pump. This means you may replace your coolant pump due to electrical failure. The most common problem with these pumps is a fault code for coolant pump volume. If you remove the water pump from your E90 and plan on reinstalling it, store it with coolant inside, otherwise it will corrode and fail shortly after reinstalling it. Always replace aluminum fasteners each time they are removed and never reinstall a questionable coolant hose.
This can be a tough part to change as it is tucked away and behind many components. I like to remove the radiator when I have to replace a water pump, it adds time to the job, but makes it a lot easier. If you have an all wheel drive E90 or one with active steering, you’re going to have to remove the radiator anyway. So I say just go for it and make your life easier no matter which model you own.
In this article, I’ll go over the steps involved with replacing the water pump on BMW E90 models. Be sure to work with a cool engine and confirm the cooling system lacks pressure before opening cooling system.
Remove engine splash shield. See our tech article on splash shield removing.
Drain cooling system. See our tech article on cooling system draining and filling.
Remove thermostat. See our tech article on thermostat replacing.
Working at the back of your water pump on right side of engine, loosen both hose clamps (green arrows)
Once all the fasteners have been removed, remove the water pump from engine. Install new water pump and evenly tighten fasteners. Install coolant hoses and tighten clamps. Connect water pump electrical connector. Pay close attention to electrical connector. Once you think it is installed, try to pull it off. I found that the seal inside the connector can swell from oil contamination; this inhibits the connectors ability to fully seat and lock into place. If it will not lock into place, replace the seal on the electrical connector. It can be replaced separately from connector. Install thermostat, radiator and cooling fan. Install splash shields and fill and bleed cooling system. Remember to check cooling system for leaks and top up coolant when complete.