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FCP Euro Service Kits

FCP Euro Kits

In last week's article, I discussed a very unfortunate situation in which the shaft bearing of the water pump on my M103 Mercedes engine disintegrated and was ejected through the front of the pump housing. After removing the belt and inspecting the pulley, it was clear that the only course of action was to replace the pump. Replacing the pump is not a complicated job, but it is in a tight space, so we must start by removing the pulleys in our way. The procedure for removing all of the necessary front pulleys is the same as in my previous article "Mercedes 6-Cylinder M103/M104 Belt Tensioner Replacement." If you have already removed your pulleys once before, as in replacing the tensioner, the bolts may not be as tight, and may come away with a little coaxing. My preferred method is to bind one bolt against the other using a screwdriver. (If you have not changed your tensioner, but find yourself replacing your water pump, I very highly recommend changing the tensioner assembly while you have it out).


Removing the circled bolt will allow the power steering pump to tilt out of the way.
Removing the circled bolt will allow the power steering pump to tilt out of the way.

 

Removing the pulleys and the tensioner assembly will give you great access to the water pump, but unfortunately, the power steering pump bracket will not allow you to complete the removal, as the flange for the tensioner bolt will be in the way. This situation can be alleviated by removing the bolt and nut from the power steering bracket which is directly above the bolt that held the tensioner in. With this bolt out of the way, the power steering pump and bracket will tilt several degrees, allowing for the removal of the pump. Carefully remove the coolant hoses if you have not already. Because the water pump is quite high in the cooling system, plenty of coolant will remain in the block if you only drain from the radiator. The block drain is on the passenger side of the engine, but was unusable in my case. I suctioned my coolant out through the water pump opening and took great care to catch any additional drippings after removing the pump.

 

Replace and seat the dipstick tube properly

There are four bolts securing the pump to the block - three of which are 13mm and the fourth is an Allen-type bolt that will require a 7mm Allen wrench. A normal L shaped Allen wrench is suggested, as space is tight. A ratcheting 13mm wrench will certainly come in handy here as well. If you find yourself needing to remove the dipstick tube to access the upper rear bolt, be absolutely sure to replace the dipstick tube and seat it properly before removing the pump, as the coolant will tend to run right over the opening and can cause you great trouble if coolant finds its way into the oil pan.

Pictured here is an assortment of useful tools for removing the stuck heater pipe.

A small bit of wiggling may be necessary to break the pump free, but be aware that there are locating collars on the front lower and rear upper bolt holes. Gently remove the pump, and thoroughly clean the O-ring mating surface. The hole left behind by the water pump is a window into your block, and may show corrosion, scale buildup, deposits, or, if you're lucky, clean cast iron. If your cooling system seems to be having trouble upon inspection of the water pump port, it may be helpful to investigate cleaning or flushing solutions recommended by the manufacturer. Mercedes-Benz offers several cooling system solutions that are quite strong, but very effective in cleaning your block and heads.

Pictured here is the hole in the block that the water pump fits against. The four water pump bolts are visible.
 
Pictured here is the hole in the block that the water pump fits against. The four water pump bolts are visible.
 
The heater pipe and sheet metal flange. The flange is week, but provides a good surface to work against while wiggling the pipe out.
 
The heater pipe and sheet metal flange. The flange is week, but provides a good surface to work against while wiggling the pipe out.

 

If you find yourself in the difficult position of having the heater pipe stuck to your old pump, you may have to resort to extreme tactics to disconnect the two. Since my old pump was going to the recycler anyway, I used the heat from a propane torch and periodic shock loads with a hammer on the pump body. The pipe eventually came free, but not without a struggle. Replace the o-ring, and join the pipe to the new water pump.

 

Operate the engine with the coolant cap off

With a new o-ring and a clean mating surface, place the new pump in the position of the old pump, taking care to replace the stubby rubber hose that goes from the upper pump outlet to the cylinder head. Replace all other pieces as they were removed, and be very sure to put a small amount of RTV or sealing compound on the inboard tensioner bracket bolt, as it seals against the engine timing cover. Refill with Mercedes-Benz approved coolant to the proper ratio, and be sure to evacuate all air from the cooling system before driving (there are several methods for “burping” the cooling system on this vehicle- I have had luck with operating the engine with the coolant reservoir cap off and heater turned on until the thermostat opens). For the first several miles, be extra diligent in keeping track of your engine temperature, as gas pockets may still be present and can cause dangerous temperature spikes if not addressed.

The M103/M104 engine is a tough piece of iron which, with proper maintenance, can last a very long time. Replacing a water pump on this engine is not terribly difficult, but is a bit more involved than on others. With a little patience, the right tools, and the right parts, this is a job that can be tackled by a novice in a few short hours.

 

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Written by :
Dan Bullmore

Dan Bullmore is a physicist and engineer from Houston, TX. Preferring the old to the new, Dan has owned many examples of Mercedes and Volvo vehicles and has devoted much of his time to maintaining and understanding them.


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