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From: "Pete Read" <>
To: "Mformation" <> Subject: E28 M5, E24 M6 Cooling System: hoses/clamps, thermostat, radiator,
water pump
Date: Tue, 2 Mar 1999 16:37:55 -0800

While I'm thinking about cooling systems, I've included some information that I put together for the M-Register newsletter last year (see below).

Since my write-up, my thermostat failed and I got to take some of my own advice. I ordered the $25 "OEM factory replacement" from Bekkers, but it wasn't the correct Wahler 4231.80. It looked like it would fit, but didn't seem to be nearly the same quality as a typical BMW Wahler or Behr thermostat. By that time, a driving school was fast approaching, so to reduce risk, I just ordered the standard M5 parts from a local dealer.

I knew the older big six thermostat would fit, but there was still some question in my mind about the square cross-section o-ring versus the round cross-section o-ring from the M5. The o-ring groove turned out to be square, so there's no reason why the cheap square-section o-ring won't work fine ($1 versus $14).

So to recap my cheap thermostat advice, just buy the old big six thermostat and o-ring (like Paul Hahn did), plus the tiny o-ring that only fits the M5/M6.

Quan Part Number      Description                    Price
---- ---------------  ---------------               -------
 1   11 53 1 254 065  Thermostat 80 C               $14.31
 1   11 53 1 250 399  Thermostat o-ring               1.03
 1   07 11 9 906 328  Thermostat small o-ring         0.30

...Cooling System write-up, M-Register Newsletter January 1998...

I changed my radiator and hoses several years ago, so some of the details are forgotten. Hopefully the basics I remember plus a list of parts and prices from the fiche, and some tips from Paul Hahn, John Hartge and Carl Nelson will be enough to get you through the job.

Thanks especially to Carl Nelson for all his advice including researching the older big six thermostat compatibility with the E28 M5. Keith Wollenberg highly recommended Carl for technical advice and parts and I've certainly been impressed. Carl is in San Diego, CA at CNPR/La Jolla Independent, 800.466-8184.

Draining Coolant

The only coolant drain found on every M5 is the engine block plug. It is located under the exhaust manifold near the number six cylinder, just like the standard 535i.

The parts fiche shows a radiator drain bolt, but most M5 radiators do not have one. Carl Nelson says the drain bolts on early radiators often froze in place and could not be removed, so they were omitted on later radiators. The lower radiator hose is not very low, so the only way to drain the radiator is by removal or siphoning.

Paul Hahn found that a good partial drain can be done with a 1/4 inch siphon hose inserted down through the radiator hose opening. He also was able to siphon much of the block by inserting the same size small hose through the hose attached to the underside of the overflow tank.

Siphoning saves time, but the most thorough drain is with the block plug and radiator removal. It is a messier job, but the block plug (19mm wrench) and radiator aren't very hard to remove. Radiator removal also makes it easier to change some hoses.

Only the seal ring for the block drain plug needs replacement when draining the system. A tip from Steve Morey is that the drain plugs are perfect for plugging the rear load leveling accumulators when eliminating the load leveling system.

Quan Part Number      Description                    Price
---- ---------------  ---------------               -------
 1   07 11 9 963 200  Plug seal ring A14x18          $ 0.30
 1   07 11 9 919 228  Block drain plug AM14x1.5        0.75

To remove the radiator:

  1. Remove plastic fan clutch shroud (two phillips screws)
  2. Remove fan clutch (32mm wrench)

    My $20 32mm Craftsman combination wrench just barely fits. Width of the wrench is 0.48 inch. A 1 1/4 inch SAE wrench will also fit if it is thin enough. Remember that the fan clutch has left hand threads -- turn wrench clockwise when facing the engine while standing in front of the car.

  3. Disconnect wires from the two temperature sensors on the driver's

    side of the radiator.

  4. Remove radiator hoses (hose clamps). Take special care with

    the small bleed hose. Too much force can easily break the small plastic nipple.

  5. Remove two bolts (10mm wrench) and lift radiator straight up.

Cooling System Hoses and Clamps

Heater hose access requires intake plenum removal (see instructions above). John Hartge suggests attaching the short water pump hose to the thermostat housing first as it makes alignment easier. My "-827 bypass pipe inlet elbow hose" failed first. It's just in front of the #1 exhaust pipe, so I imagine the extra heat helped its demise.

Note that M5 and M6 hoses are the same except for the hose from the plastic tee to the expansion tank. The five series parts fiche incorrectly shows the part number from the M6. You can make it work by twisting it a little -- that's what I did. Stan Simm noted this problem in the July '94 MPower. Both the M6 and the correct M5 part number are included below.

Quan Part Number      Description                    Price
---- ---------------  ---------------               -------
 1   11 53 1 306 828  Water pump to t'stat hose     $10.13
 1   11 53 1 306 829  Bypass pipe to t'stat hose     11.57
 1   11 53 1 306 832  Radiator to t'stat hose        32.77
 1   11 53 1 306 850  Heater return to t'stat        21.67
 1   11 53 1 306 851  Expansion tank to T hose       30.80 (M6 only)
 1   11 53 1 284 598  Expansion tank to T hose        8.53 (M5 only)
 1   11 53 1 310 625  Radiator hose, pass side       44.53
 1   11 53 1 306 827  Bypass pipe inlet elbow hose   22.72
 1   64 21 1 374 635  Heater outlet hose             14.25
 1   64 21 1 374 636  Heater inlet 1 hose            15.33
 1   64 21 1 374 637  Heater inlet 2 hose            11.85
 1   17 12 1 712 736  8x13mm vent hose (per meter)   12.03
 8   16 12 1 180 237  L10-16mm hose clamp             0.35
 4   07 12 9 952 111  L23-29mm hose clamp             0.40
 6   07 12 9 952 113  L26-33mm hose clamp             0.45
 3   07 12 9 952 115  L32-38mm hose clamp             2.00
 7   07 12 9 952 121  L47-54mm hose clamp             2.00

Thermostat Operation

The thermostat housing has four main hoses plus a small bleed hose which makes the system self-bleeding. Three hoses return coolant to the housing, while the short lower hose pulls coolant from the housing back into the water pump. The water pump then forces coolant back into the block.

On the passenger side of the thermostat housing is a bypass tube which crosses the front of the engine. Coolant bypasses the radiator this way, traveling from the passenger side towards the driver side, when the thermostat is closed. Entering from the back is the heater/expansion tank return. Finally, on the driver side is a large radiator hose.

As the thermostat opens, the "button" on the end closes off the bypass tube. Coolant then travels through the radiator, hot fluid entering on the passenger side and relatively cool fluid returning to the thermostat housing from the driver's side where it's pulled back into the pump again.

Looking at the M5 thermostat and o-rings listed below (don't forget the small $0.30 o-ring), you'll notice that they are priced like real M-parts -- $50 for the thermostat alone.

Paul Hahn replaced his M6 thermostat with an older big six thermostat p/n 11 53 1 254 065, list price $14.31. This interested me so I borrowed John Hartge's old broken M5 thermostat and compared it with a new -065 thermostat at the local BMW dealer (they don't stock the M5 thermostat). The only obvious difference is the "button" size with the M5 being a smaller 30mm versus 35mm.

Next I checked with Carl Nelson. At first he was concerned about thermal shock at warm-up from the different sized buttons. Then he measured an M5 housing and convinced himself that the larger button on the -065 thermostat will work fine.

I also checked with long time M-Register member Mark Luttrell at Bekkers Import in Albany, GA 800.624-5410 x11. Bekkers has a direct OEM source for M5 thermostats as they are able to sell both the thermostat and o-rings together for less than $25 (versus $65 list price).

Quan Part Number      Description                    Price
---- ---------------  ---------------               -------
 1   11 53 1 307 737  Thermostat 80 C               $49.34
 1   11 53 1 304 202  Thermostat o-ring              13.88
 1   07 11 9 906 328  Thermostat small o-ring         0.30

Radiator, Water Pump

Like the rest of the cooling system, the radiator and water pump are specific to the M5/M6. The cap is also higher pressure, 1.4 bar versus the 1.0 bar of the normal big six engine. After checking the radiator price, be sure to read David Hutton's radiator repair article (see below).
Quan Part Number      Description                    Price
---- ---------------  ---------------               -------
 1   17 11 2 226 018  Radiator                     $850.45
 1   17 11 2 227 683  Radiator cap, 1.4 bar           9.69
 1   11 51 1 312 539  Water pump                    131.95
 1   11 51 1 265 654  Gasket, water pump              0.73

Pete Read
'88 M5
Arlington, VA

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