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:
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.
side of the radiator.
the small bleed hose. Too much force can easily break the small plastic nipple.
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
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
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
