«The victim.err, I mean “Subject Vehicle”. My 1998 M3 at 89,000 miles. A little background: The cooling system for the E36 3 Series has developed ...»
System Overhaul DIY
BMW E36 Cooling
’ve been seeing a lot of threads on bf.c lately asking about doing a cooling system overhaul on an
E36 Bimmer. I wrote this DIY a while ago, but never did anything with it. So, I thought I’d post
it here. I actually did this job about 2 years ago and so far, it’s still holding up. After about a year,
the new water pump began to leak but the vendor replaced it at no charge. I actually referred back to
this DIY for a refresher on changing it out. It went much faster the second time around! Not that it took very long the first time. Total time from start to finish was about 5 hours. Other than replacing the thermostat and flushing the coolant, I had never done any kind of work on the cooling system and compiled the instructions for the job from what I found online and my Bentley manual. I used regular hand tools for the entire project.
The victim…err, I mean “Subject Vehicle”. My 1998 M3 at 89,000 miles.
A little background:
The cooling system for the E36 3 Series has developed a reputation for suffering (sometimes catastrophic) failures well before reaching 100,000 miles. The problems include cracked and leaking radiator hose fittings, cracked thermostat housings, sticky thermostats, failed water pump bearings, and leaky water pumps. Some earlier models also suffer from failed plastic water pump impellers. There doesn’t seem to be a consensus on exactly when the impeller was switched to a more robust metal version. The older plastic design is prone to slipping on the shaft, having the impeller blades wear down, or, in some cases shattering, sending shrapnel throughout the engine. Knowing this, I decided to overhaul the entire cooling system since most of the components are at risk for failure. Since the related jobs are much easier with the radiator out of the way, it made sense to do the entire overhaul at the same time. The subject vehicle for this article is my 1998 M3 with 89,000 miles on the odometer. For this project I’ll be replacing the radiator, water pump, thermostat, thermostat housing, upper and lower radiator hoses, serpentine belt, and all associated seals and gaskets.
The upper neck on the plastic portion of the radiator is cracked at the hose fitting and leaking. The leak is slow and only requires the coolant to be topped off about once a month. But it can fail catastrophically at any time.
I’ve changed radiators on other cars, and thermostats on BMWs as well as others. I’ve never changed a BMW radiator or water pump before. But again, my purpose for documenting this procedure is to show that you needn’t be an expert to perform these tasks! Before getting started, I should probably also point out that the procedures outlined apply to 6-cylinder E36 cars in general, and the S52 M3 specifically. There very well may be variations in the details based on model and production date.
4-cylinder models share a similar procedure, but use a different arrangement for the cooling fan.
These are the parts replaced in the cooling system overhaul: (A) Radiator, (B) BMW coolant (only use BMW coolant!), (C) water pump and O-ring, (D) thermostat, (E) serpentine belt, (F) thermostat O-ring, (G) thermostat housing seal, (H) lower radiator hose, (I) upper radiator hose, (J) metal thermostat housing, (K) radiator clips, (not pictured) AC compressor drive belt, Radiator Hose Clamps.
The first step is the same as for any vehicle maintenance project: Park the car on a hard, level surface with good lighting and securely set the parking brake. I also chock the rear tires. While it’s not absolutely necessary to raise the car, it does make draining the radiator easier. Please use proper jacking precautions if you raise your car. All 4-Door E36s have a service position for the hood. This allows the hood to open to a near-vertical position, which helps access. At the top of the driver’s side hood strut, remove the bolt locking the secondary hinge. Then simply raise the hood to the service position. The next step is to drain the coolant from the radiator. Depending on the condition of the lower shroud, you may or may not have to remove it. The drain plug is located on the bottom edge of the radiator, on the driver side facing the rear of the car. Place a drain pan under the drain and remove the plug. It’s made of plastic and should come out easily. Once coolant has begun to flow out of the drain, remove the cap from the top of the expansion tank. Unless you plan to do a complete coolant flush, it’s not necessary to drain the engine block, just the radiator and main coolant hoses. Despite your best efforts to contain spills, this will be a messy job. I placed a large piece of cardboard under the car to try to absorb at least some of the lost coolant. It will be helpful to have a bag of absorbent on hand (kitty litter also works well). Bear in mind that spilled coolant is toxic to humans and pets.
At the top of the driver’s side hood strut is the service-position hinge. Removing this bolt allows the hood open nearly vertically. This allows for better access and light. The bolt is actually installed on the other side of the hinge, but I threaded it back into the hole so I wouldn’t lose it!
Remove the front shroud from above the radiator. 4 screws and 2 expanding plastic rivets secure it.
The cooling duct for the alternator attaches to the back edge of this shroud. It’s helpful to remove the cooling duct by loosening the hose clamp holding it to the alternator. This would also be a good time to vacuum out the collection of bugs and leaves gathered in the back of the alternator.
The front shroud cover must be removed first. Arrows show locations of 4 metal screws (E) and 2 ex panding plastic rivets (D). It also helps to remove the alternator cooling duct (G). Other items of inter est: Expansion tank cap (A), bleed screw retainer (B), bleed screw (C), fan shroud (F).
The two large coolant hoses are removed next. Even if you are careful removing the hose clamps, they should be replaced. They are inexpensive – but note that there are two different sizes. One hose leads from the upper radiator neck to the thermostat housing. The other leads from the thermostat housing to the lower radiator neck. If you aren’t planning to replace the thermostat housing, be very careful not to damage it while removing the hoses.
Removing the cooling fan and its clutch is necessary to gain access to the water pump, and the radiator cannot be removed with the fan in place. You’ll need a 32MM open-end wrench to loosen the fan clutch nut. Unless you happen to live in a larger city, you may have trouble locating one. I sure did!
But it turns out that 32MM is equivalent to 1-1/4 inches, and that may be an easier wrench to find.
I ended up borrowing one from a friend who is a tractor mechanic. Loosening the 32MM fan clutch nut is one of the few parts of the job that recommends a special tool. I got by without it, though. You see, the fan clutch attaches to a threaded shaft on the water pump, but the fan will free-spin with the engine off, so the water pump needs to be locked in place to loosen the nut. BMW has available a tool specially designed to lock the pulley, but it costs about $40 and, for me anyway, wouldn’t get used much. There is an alternative that’s a little more work, but it’s not I job I intend to do very often so I’d rather save the money. The water pump pulley has four bolts on the front that hold it to the water pump. A long-handle screwdriver with about a 3/16 inch diameter shaft can be wedged between two of the bolt heads and then jammed up against one of the idler pulleys. This is an effective way to prevent the water pump from turning. Remember that the nut is left-hand threaded, which means that the wrench handle should be turned clockwise when standing in front of the car looking at the front of the engine. It’s also important to note that the fan clutch is fluid-filled and should be stored in a vertical position to prevent any leakage.
Wedge a long-handle screwdriver (B) between the bolts on the water pump pulley. Then, use a 32MM or 1-1/4 inch open wrench (A) to loosen the fan hub nut by turning it clockwise (reverse-threaded).
With the fan and clutch removed, the radiator is the next part to come out. There is a plastic retaining clip on either side of the radiator securing it to the frame at the front of the engine bay. A flat-bladed screwdriver inserted into the slot in the top of the clips removes them easily. Neither of mine broke when being removed, but the plastic can become brittle. Replacements only cost about $4 each, so it might be wise to add a couple to your parts order. There are two expanding plastic rivets holding the fan shroud to the back of the radiator. They are in the upper corners and should be popped out next.
There are two hoses that run inside the fan shroud and attach to the expansion tank. The small hose at the top of the radiator can be left attached to the expansion tank, but must be disconnected from the radiator. The larger hose at the bottom of the expansion tank must be removed from the tank, but left in the car. To remove the expansion tank, unscrew the bleed screw and remove it. There are two small clips in the plastic housing for the bleed screw. Carefully squeeze them while prying out the retainer for the bleed screw. The expansion tank can now be removed and set aside. Now the fan shroud can also be moved out of the way. I pulled the hose through it enough to allow the shroud to rest on top of the engine, but I didn’t remove it entirely. There are two rubber “feet” on the bottom of the radiator where it rests on the car’s frame, and two rubber mounts that fit into slots at the top. Be sure to save them so you can transfer them to the new radiator!
Two plastic clips secure the radiator to the front frame. Work a flat-blade screwdriver into the slot in its top to release the clip. It can then be slid out of the way.
Before you throw away the old radiator, be sure to save these rubber mounts. You’ll need to transfer them to the new one.
The thermostat housing is held in place with four bolts. One of the three is larger and passes through a bracket. The bracket is held in place by a second bolt. Loosen that bolt to move the bracket out of the way to make removal of the thermostat housing easier. With the thermostat housing removed, a flat-blade screwdriver can be used to pop the thermostat out. I stuffed some shop rags in the inlets, then used a razor blade to carefully scrape the surface smooth. Before installing the new thermostat, wet the O-ring with coolant. Then also wet the new thermostat housing seal with coolant and reassemble the thermostat housing. Don’t put the hoses back on yet, though!
Remove this bolt (A) to get bracket out of the way to make it easier to extract the thermostat hous ing. (B) Water pump pulley. (C) Thermostat Housing. (D) AC compressor belt tensioner. (E) Serpentine belt tensioner. If you stuffed rags in the thermostat inlet openings, remember to remove them!
The water pump pulley is held in place with four 10mm bolts. It’s better to loosen them with the serpentine belt still in place – it keeps the pulley from turning! With the bolts loosened, but not removed, pop the plastic cap out of the centers of the two belt tensioners. Even if you don’t plan to replace the AC compressor belt, you still have to remove it to get the serpentine belt out. If you don’t plan to replace the serpentine belt either, just slip it off the water pump pulley and leave the AC compressor belt in place. Note: BEFORE removing the serpentine belt, take a photo or draw a sketch of how it’s routed – It can go back on several ways, but only one is correct! To release the belt tension, use an 8MM allen wrench or a socket wrench with an 8MM hex adapter. Using firm pressure, push the wrench clockwise to move the tensioners. They are spring-loaded and will return to their original position when pressure is released. With the belt off the pulley, remove the four bolts and pulley. The water pump itself is held to the engine block by four 10MM nuts. There are also two threaded holes on either side of the pump housing. With the 10MM nuts removed, thread an M6 bolt into each hole – I found a 3-pack of M6 bolts at Autozone for about $2. Tighten each bolt evenly to push the pump out of the block. When it comes out, coolant with gush out of the opening – so be ready!
The belts must be de-tensioned to remove and reinstall them. The tensioners are spring-loaded and release by inserting an 8MM hex key (allen wrench) and turning clockwise. Inset: An 8MM hex adapt er fits a socket wrench, giving better leverage than an allen wrench and makes de-tensioning the belts easy.
What’s wrong with this picture? There are two threaded holes in the water pump housing to help remove it. An M6 bolt (yeah, I know – M6!) is threaded into each and tightened to force the pump out of the engine block. It works better if you remove the four bolts attaching the pump to the block! It took me a minute to figure out why the pump wasn’t moving as the M6 bolts got tight.
Wet the new water pump O-ring with coolant and put it on the new pump. Push the pump into the engine block (it’s a tight fit and will take some effort), then reinstall the four retaining nuts. Replace the pulley and snug down the four nuts. Either install the new serpentine belt, or slip the original one back on the water pump pulley – remember to release the tensioner first! I replaced the AC compressor belt because it had some cracks and I had to take it off anyway. If you removed it, put it back on now. Once the serpentine belt is in place, tighten the four bolts securing the water pump pulley to the water pump. The new water pump may have a plastic cap covering the threads for the cooling fan. If it does, be sure to remove that now.
Transfer the temperature sensor, rubber “feet”, and slotted rubber mounts from the old radiator to the new one. Be very careful when handling the new radiator. It is very easy to damage the cooling fins!