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From: "Pete Read" <pete.read_at_boeing.com>
To: "Mformation" <mformation_at_halcyon.com>
Subject: E28 M5, E24 M6 Cooling System: hoses/clamps, thermostat, radiator,
water pump
Date: Tue, 2 Mar 1999 16:37:55 -0800
Status:
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:
- Remove plastic fan clutch shroud (two phillips screws)
- 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.
- Disconnect wires from the two temperature sensors on the driver's
side of the radiator.
- Remove radiator hoses (hose clamps). Take special care with
the small bleed hose. Too much force can easily break the small
plastic nipple.
- 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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