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Pelican Technical Article:

Cooling Hose Replacement

Tom Morr

Time:

1 hour1 hr

Tab:

$64 to $95

Talent:

*

Tools:

7mm socket/ratchet or nut-driver or flat-blade screwdriver, possibly pliers

Applicable Models:

Mercedes-Benz SLK230 (1998-04)

Parts Required:

Replacement hoses

Hot Tip:

Flush the cooling system when changing hoses

Performance Gain:

Fixes or prevents coolant leaks

Complementary Modification:

Replace thermostat, hose clamps

People often wait until cooling hoses fail to change them. This lack of preventive maintenance can cause harmful engine overheating. A tow truck and other inconveniences often accompany blown-hose incidents.

Like drivebelts, hoses should be visually inspected periodically. Engine heat causes rubber to deteriorate over time. Vacuum lines, fuel hoses, and cooling hoses are all susceptible to degradation. A general rule of thumb is to check all under hood hoses about every six months or 6,000 miles.

Cooling hoses are easy to check and service at home. Some of the hose clamps are accessed from underneath, so raising and securing the car's front end is recommended. Be sure to consult the article on jacking up your vehicle safely before you get it up in the air and on jackstands.

Hose replacement normally requires draining the coolant, which is addressed here, along with cooling-system flushing:

http://www.pelicanparts.com/techarticles/Mercedes-SLK230/32-WATER-Coolant_Flush_and_Replacement/32-WATER-Coolant_Flush_and_Replacement.htm

With the engine cool, look at all hose ends. Check for swelling around the clamps, cracked or frayed edges, and moist or oily ends. Look along the length of the hoses for flat or chafed areas. Verify that the hoses aren't contacting moving parts. Squeeze the radiator hoses every few inches. Soft spots indicate internal deterioration. Hairline cracks can also reveal themselves during squeezing. Leaks are often indicated by white or rusty deposits along the hoses or at their ends.

Check for loose clamps. Stainless-steel worm-gear-style clamps can often be reused: they typically have longer service lives than wire-style clamps. Still, some M-B owners make a practice of replacing clamps with the hoses. Pelican Parts offers OE-spec worm-gear clamps.

If the coolant is fairly fresh, it can be captured and re-used. Coolant is toxic. Many pets like its taste, but coolant can do severe kidney damage. Keep coolant secure and dispose of it properly.

Spending a few extra minutes flushing the cooling system before refilling it can't hurt. Some purists use distilled water for this; most flush the engine with tap water.

M-B offers cooling system flush products to help degrease and descale the engine and radiator: A001-986-21-71, 000-989-10-25. Most enthusiasts flush their coolant every 2-3 years. A thorough flush involves removing the plug in the engine block.

When refilling the expansion tank, consider using official MB coolant. It costs more than popular parts-store brands but is formulated for maximum compatibility with the engine's alloys. Potential extended head-gasket life more than compensates for the additional coolant expense.

If time and/or budget are constraints, Zerex G-05 anti-freeze is factory-approved by M-B. Zerex is M-B's factory fill in some countries. We couldn't verify that Zerex is chemically identical to M-B-branded coolant, but it does meet M-B's specifications.

A 50/50 mix of coolant and water is recommended -- mineral content in tap water varies widely. Coolant capacity of the MB 2.3L engine is approximately 10 quarts, about two of which live in the heater core. Air will need to be "burped" from the system after the coolant is refilled.

Preliminaries include raising the car's front end and removing the lower engine cover.
Figure 1

Preliminaries include raising the car's front end and removing the lower engine cover. With the engine cold, remove the expansion tank's cap to de-pressurize the cooling system.

The radiator drain plug is red and located on its lower left corner.
Figure 2

The radiator drain plug is red and located on its lower left corner. It loosens counter-clockwise with a flat-blade screwdriver.

The petcock system includes a hose-attachment nipple on the radiator's back side for cleaner coolant draining.
Figure 3

The petcock system includes a hose-attachment nipple on the radiator's back side for cleaner coolant draining. We had a wide catch pan, so we went rogue and drained direct.

When mixed with distilled water, the OEM coolant can last as long as 150,000 miles or 15 years.
Figure 4

When mixed with distilled water, the OEM coolant can last as long as 150,000 miles or 15 years. So, clean coolant can often be reused. Always contain coolant to prevent kids and pets from drinking it. Dispose of out-of-service coolant properly -- not on the ground or in the gutter. Some service stations, parts stores, or municipalities will accept it, similar to waste oil.

The factory cooling system hose clamps have 7mm heads.
Figure 5

The factory cooling system hose clamps have 7mm heads. A nut-driver is the preferred tool, although a ratchet or a flat-blade screwdriver will also work. The upper radiator hose's clamps are easily accessible (green arrows). We placed the cap on the expansion tank to keep dirt out.

Hoses will normally twist and slide off their inlet and outlet ports by hand.
Figure 6

Hoses will normally twist and slide off their inlet and outlet ports by hand. Specialized hose-grip pliers are available to expedite the process. If the hoses are stuck and are being replaced anyway, they can be carefully cut away. Residual corrosion should then be cleaned off the nipples, taking care to keep any flakes from getting into the radiator or engine.

The lower radiator hose clamps to the water pump, under the front engine cover.
Figure 7

The lower radiator hose clamps to the water pump, under the front engine cover. Also check the rear hose on the water pump, which leads to the heater valve.

This hose is still serviceable but is beginning to swell around the clamp.
Figure 8

This hose is still serviceable but is beginning to swell around the clamp.

The lower radiator hose is accessible from underneath without having to remove any additional parts.
Figure 9

The lower radiator hose is accessible from underneath without having to remove any additional parts. The expansion tank's main hose also connects to the radiator, just above the main hose. Inspect it while underneath.

The expansion tank's upper clamps and short hose are easy to inspect and access from the top.
Figure 10

The expansion tank's upper clamps and short hose are easy to inspect and access from the top.

Heater hoses are easier to change with the coolant drained.
Figure 11

Heater hoses are easier to change with the coolant drained. Check the condition of the hose leading to the heater core (green arrow).

Also check the heater hoses at the valve, on the right side of the engine compartment on the bumper side of the battery.
Figure 12

Also check the heater hoses at the valve, on the right side of the engine compartment on the bumper side of the battery. Pliers can be used to remove the spring clamps.

Flushing is its own story, but cooling hose changes provide an opportune time to muck out the cooling system.
Figure 13

Flushing is its own story, but cooling hose changes provide an opportune time to muck out the cooling system.

Refill the expansion tank with a 50/50 coolant/distilled water solution.
Figure 14

Refill the expansion tank with a 50/50 coolant/distilled water solution. Topping off the coolant through the upper radiator hose before reconnecting it will help minimize the air in the system. With all hose clamps tight but not over-torqued to the point of bulging the hoses, run the engine with the heater on full-blast. Check the hoses for leaks, particularly around the clamps. After the thermostat opens, squeeze the upper hose a few times to "burb" remaining air out of the system. (Wear gloves--the hoses get hot.) Top off the coolant to the proper level. Check the level again after driving the car and top off as necessary.

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