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E36 cooling system complete overhaul — every part you need to replace

CCraig

@coolant_craig

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The E36 cooling system is a ticking time bomb if you havent replaced everything. These cars are 25-30 years old now and every rubber and plastic component in the cooling system is on borrowed time. Here is the complete list of what to replace:

  1. Radiator (aluminum aftermarket recommended over OEM plastic)
  2. Expansion tank (the number one failure point — always cracks)
  3. Water pump (metal impeller, not plastic)
  4. Thermostat (Wahler or Behr OEM)
  5. All coolant hoses (upper, lower, heater hoses)
  6. Radiator cap
  7. Temperature sensor
  8. Fan clutch (if mechanical fan)
  9. Auxiliary fan and relay

Total parts cost: 300-500 EUR depending on brand choices. I recommend doing everything at once — if one component fails, the rest are not far behind.

The expansion tank is the most critical. When it cracks (not if, when), you lose all coolant in minutes and the engine overheats. I have seen M52 engines destroyed because of a 30 EUR expansion tank.

Pro tip: carry a spare expansion tank and a jug of coolant in the boot. It has saved me twice on long trips.

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  1. #1
    RRodBearingRick

    @rod_bearing_rick

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    The S52 gets a bad reputation but it is actually a very reliable and tuneable engine. With a set of S50 cams, a tune, and headers, you can get close to 280hp. Not S50B32 territory but still very respectable for a naturally aspirated inline six.

    For anyone buying an E36 M3 — check the subframe mounting points regardless of engine. This is the biggest structural issue on these cars and repair costs can exceed the value of the car if caught late.

  2. #2
    GGreg

    @gasket_greg

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    Cannot stress enough how important the expansion tank replacement is. I have seen three M52 engines killed by expansion tank failures. The OEM plastic tanks become brittle and crack without warning. When they go, you lose all coolant in under a minute.

    Always use a genuine BMW or Behr replacement — the cheap aftermarket ones crack even faster. And yes, carry a spare in the boot. It is the single best insurance policy for any E36 owner.

  3. #3
    TTheo

    @thermostat_theo

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    This is an excellent guide. I would add that the thermostat housing on the M52 and M50 engines is also a common leak point — the plastic housing cracks over time. Replace it with an aluminum aftermarket unit from Mishimoto or similar. About 60 EUR and it will never crack again.

    Also, when doing the cooling system overhaul, flush the heater core. A clogged heater core reduces cabin heating and can mask a coolant flow issue. Use a garden hose to back-flush it until the water runs clear.

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