Monday, October 4, 2010

Thermostat and Water Pump replacement on a 93 BMW 525i

I try and stay away from making posts about stuff that you can readily find in the Bentley manual. The information in the Bentley concerning the Thermostat and Water Pump are very adequate and if you follow that information you will be able to complete these jobs with no problem.

What I thought that I'd do in this post is give a few tips I've discovered while doing these jobs four different times now.

The reason I did the replacement of the thermostat and water pump so soon is because I developed a leak. Actually it was leaking for a good year or so, but only occasionally. Once in a while I'd notice some coolant on the ground, I couldn't tell where it was coming from exactly, but I knew it was from the front of the engine, so more than likely it was the water pump. I like to change out the thermostat when I do a water pump since I've got everything apart anyway, so I ordered the things I needed. I got a new water pump, thermostat and housing, radiator hoses and belts. I could tell the belts were getting wet from the leak and figured it would be a good idea to change them out too.

Here are some tips that should make your job a bit easier if you have the Bentley and follow it.

To get to the water pump and thermostat, you need to remove the fan and housing. They say you need a special tool to hold the fan pulley, but you don't really need it. I used a 1 1/4" open end wrench to loosen the fan nut. Remember, it is a left hand thread, so you turn it the opposite way to loosen it. Here is the tip you can use to get it loose without the special tool. If you look at the picture below, you can see where I've drawn the arrows. Take a mallet, I used a rubber one and hit it in the direction shown. It probably won't break loose the first time, maybe not even the 10th time, but it will eventually break loose. I started using a propane torch to heat up the fan nut so it would break loose easier. If it won't come loose without it, try the heat.

This pic shows the location of the fan nut without the wrench:

This pic shows with the wrench:

With the fan and housing removed, you can now proceed. Before you attempt to remove the thermostat housing or water pump, you need to drain the coolant out of the system.

Here are a couple of tips that might help.

First off, I jack up the front end of the car and put two buckets under the radiator, see pic:

Make sure all of your heater settings in the car are set to HOT, best way to do this is to turn on the key, turn the knobs and wait for about 30 seconds and then turn off the key. Then I open the radiator drain. I completely remove the drain plug and to do that, you have to remove the retaining pin (see pic, you may not have the retaining pin, one of my 525i's was missing it the first time I did this). It drains much faster without the plug in the hole.

Make sure you remove the radiator cap too so the coolant will drain quicker.

Once the radiator is drained, you still need to drain the rest of the coolant in the block.

You do this by removing the block plug. The block plug is located on the passenger side of the motor right between the exhaust headers. Depending on how much of the original shielding you have underneath your car you may have to remove several panels to let the coolant drain properly. Both my cars had only a couple of pieces of the shielding up, so it came apart easily.

This series of pics shows the location on the block plug:



Once the coolant is drained, you can finally get down to business.

This picture shows several different things. The location of the thermostat housing and it's bolts (red arrow housing, dots are bolt locations). Yellow arrow shows threads of water pump where fan attaches to, yellow dots show bolts that hold fan pulley to the water pump. White arrows show locations of the tensioner pulley's for the belts. You will use one of a few different things to remove the belts, either an allen wrench, torx wrench or socket wrench. Just depends on how your car is set up.

Once you have the belts and radiator hoses removed, you can work on taking the thermostat housing and water pump out. Thermostat housing is easy, just remove the four bolts. The water pump can be a bit more challenging, but not that bad. If you look in the Bentley, it tells you that you need two M6 bolts to draw the water pump out of it's seat once you have removed the four mounting nuts. I looked high and low for those M6 bolts the first time I did this job. I went to the local BMW Dealer and even they didn't really know what I was talking about, but I finally ended up with what I needed. To make your job easier, the three small bolts that hold the thermostat housing on are M6 bolts and work perfectly for drawing out the water pump. You just thread them into the ears on either side of the water pump and slowly turn them a little at a time and it will draw the pump out. One of my cars didn't even need to have that done, the pump pulled out easily by hand.

If you look at the picture below, you can barely see where the M6 bolts push against to draw the pump out, I didn't take a picture of the pump installed, this is after I had already removed the pump. You can also see above where the thermostat and housing fit.

Once you get to this point, the Bentley does a very good job of instructing you on what to do. It's pretty much just reverse of the removal to install. Make sure you use BMW coolant and distilled water, not the green stuff to refill the system. All of the torque specs are listed in the Bentley and should be followed. Other than that, good luck with your project.

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