Heater hose in-line thermostat?

[Joe Gilmore]

Just bought a nice '91 318is after many years of E28.  Saw the excellent thread by ///m42sport on changing coolant hoses and am in the process of replacing all of them and the vacuum hoses.  But on my car, the shorter heater hose that goes to the firewall from the left rear corner of the cylinder head (the one with more kinks in it) has a metal gizmo in the middle of the hose--I had to cut the replacement hose approximately in half to fit it in.  The metal gizmo also has a smaller diameter hose attached that goes back into the same heater line via a T-fitting right before it enters the firewall.

I took the gizmo in to the dealer, they pulled up the picture, it's a thermostat.  Does anyone else have this, or has my car been butchered by some hack before I got it?  What the hell does it do?

[BlackBMWs]

Just bought a nice '91 318is after many years of E28.  Saw the excellent thread by ///m42sport on changing coolant hoses and am in the process of replacing all of them and the vacuum hoses.  But on my car, the shorter heater hose that goes to the firewall from the left rear corner of the cylinder head (the one with more kinks in it) has a metal gizmo in the middle of the hose--I had to cut the replacement hose approximately in half to fit it in.  The metal gizmo also has a smaller diameter hose attached that goes back into the same heater line via a T-fitting right before it enters the firewall.

I took the gizmo in to the dealer, they pulled up the picture, it's a thermostat.  Does anyone else have this, or has my car been butchered by some hack before I got it?  What the hell does it do?

I have the same one.  It's an aux thermostat.  I cut my new hose the same way.

Mine is on the left side of the part diagram on RealOEM.

http://www.realoem.com/bmw/showparts.do?model=BA73&mospid=47325&btnr=64_0135&hg=64&fg=99

There is a great post on removing a majority of the hoses, however, I just chose to replace them all as i did not want to have to figure out in the future if I had a different issue created by altering the motors original build.    

So, my question on the Aux Thermostat is, what does it do differently, if anything and how do you know if it's operating correctly?   :cool:

[Joe Gilmore]

BlackBMWs, I just saw this heater hose thermostat gizmo in teh Phil's "mess under the manifold" photos, so now I know some cars have it, but I don't know how it is supposed to be connected.  I suspect some prior hack connected it wrong, because it would be useless feeding into the same line as I have found it on my car.  Questions:

1.  The long heater hose that goes from the end of the plastic pipe on the side of the block to the firewall--Should it connect to the upper or lower heater fitting on the firewall?

2.  The small-diameter hose that goes from the aux thermostat to the T-fitting--Is the T-fitting in the long heater hose line on your car?

[BlackBMWs]

BlackBMWs, I just saw this heater hose thermostat gizmo in teh Phil's "mess under the manifold" photos, so now I know some cars have it, but I don't know how it is supposed to be connected.  I suspect some prior hack connected it wrong, because it would be useless feeding into the same line as I have found it on my car.  Questions:

1.  The long heater hose that goes from the end of the plastic pipe on the side of the block to the firewall--Should it connect to the upper or lower heater fitting on the firewall?

2.  The small-diameter hose that goes from the aux thermostat to the T-fitting--Is the T-fitting in the long heater hose line on your car?

So, I only have this one picture, as I had to buy the "j" shaped hose.


I did end up cutting the hose in the foreground going into the T fitting by about 3.5"  to become the hose on the other side of the t.

So,
the answer to question #1 is upper heater fitting.  <-----Correction  The lower hose goes from the block/head to the aux thermostat to the lower heater fitting.  Just went outside to check.  
the answer to question #2 the T fitting is on the upper hose.

Hope that helps...

Just for fun, here are most of the fuel, vaccum and coolant hoses and o-rings that were swapped out.  


BTW, I still have my E28.  Too fun to lose...  :cool:

[Joe Gilmore]

Okay, that helps a lot.  Apparently on my car somebody switched the short heater hose and the long heater hose in the past.  Putting the short heater hose on the T-fitting essentially disabled the aux thermostat, since a thermostatically controlled flow that flows back into the same line has no effect.  It makes much more sense that the small-diameter hose carries that flow into the long heater hose line.

But we still don't know why the thermostat is there, what effect it has, and how to verify that it's working correctly!  Anyone?

Mine is a 1984 533i with a '92 535i drivetrain, E32 brakes, and M5 swaybars.  I can't turn loose of it.  When I die, maybe.  Unless I can greymarket it into heaven or (more likely) hell.

[BlackBMWs]

Okay, that helps a lot.  Apparently on my car somebody switched the short heater hose and the long heater hose in the past.  Putting the short heater hose on the T-fitting essentially disabled the aux thermostat, since a thermostatically controlled flow that flows back into the same line has no effect.  It makes much more sense that the small-diameter hose carries that flow into the long heater hose line.

But we still don't know why the thermostat is there, what effect it has, and how to verify that it's working correctly!  Anyone?

Mine is a 1984 533i with a '92 535i drivetrain, E32 brakes, and M5 swaybars.  I can't turn loose of it.  When I die, maybe.  Unless I can greymarket it into heaven or (more likely) hell.

Ha!  Small world...  1984 533i, Bilstien sports, Eibach sport springs, Suspension Techniques Sways F/R, Hartuge Strut bar up front.   Actually, my wife screams around in it now, since I picked up the 540it.   She's hooked...   :cool:

[tmorinbmw]

Okay, that helps a lot.  Apparently on my car somebody switched the short heater hose and the long heater hose in the past.  Putting the short heater hose on the T-fitting essentially disabled the aux thermostat, since a thermostatically controlled flow that flows back into the same line has no effect.  It makes much more sense that the small-diameter hose carries that flow into the long heater hose line.

But we still don't know why the thermostat is there, what effect it has, and how to verify that it's working correctly!  Anyone?

Mine is a 1984 533i with a '92 535i drivetrain, E32 brakes, and M5 swaybars.  I can't turn loose of it.  When I die, maybe.  Unless I can greymarket it into heaven or (more likely) hell.

I'm having problems with the heat in my car aswell... not sure if I have the auxiliary theremostat connected properly. I DO know that they're installed by BMW dealers as a recall due to possible heater core leakage on your leg as your driving.

[ak96ss]

That extra thermostat is part of a campaign that BMW did way back when to address an issue with overpressurization of the coolant system - http://www-odi.nhtsa.dot.gov/cars/problems/recalls/relatedRecallsummary.cfm?INV_ID=EA92017&recallIdlist=93V015000&ModuleType=Vehicles