Re: M42: Thermostat or what?

[Brian Brown <bpbrown@xxxxxxxxxxxx>]

> Date: Tue, 30 Nov 1999 17:25:14 -0600
> From: "Steve Ballard" <stballard@domain.elided>
> Subject: M42: Thermostat or what?
>
> I finally decided to replace the vacuum and coolant hoses on my 1991 318is.  What a nightmare!  I had to remove the intake manifold to get to most of them.  My current dilemma is that some of the replacement water hoses don't match with the ones I purchased as replacements.  This specifically refers to the hoses that connect to the firewall.  On my car, they are routed in a complex fashion to a funny looking device that looks like a miniature version of a 2002 external thermostat.

This is a bypass valve that was installed as part of a factory recall on your car.  In combination with a new radiator cap, its purpose is to limit the coolant pressure at the heater core.  Apparently, in cases of cooling system abuse where the driver also ignored the temperature gauge, the heater core could burst and spray coolant on the drivers feet.

To install it, you will need to cut the two hoses near the firewall (just as when the recall was done).  The valve goes in the hose by the block (hopefully you can still copy its original orientation), and the 'T' fitting goes in the other hose.  A third (non-original) bypass hose goes between the valve and the 'T' fitting.

>  I ordered a replacement thermostat, however, and the one I received looks like an internal thermostat - only I can't find a place to put it.

The thermostat is in the front of the head, underneath the fitting with the large radiator hoses.

>  The replacement water hoses that I have could be made to work with the old "thermostat" but I would need to splice it in.  Exactly what in the hell is this thing?  Is it really the thermostat?  Did the parts guys sell me the wrong thermostat?  What makes this job really difficult and confusing is that I cannot locate a good schematic for vacuum and water hoses in this car.  Neither Chiltons, Bentley, nor Haynes are any help.  Can someone tell me where to find one?

The factory parts fiche or EPC CD probably have the best drawings, although they are blow up diagrams separated into several pages.  Perhaps your dealer could give you a printout.

Regards,
Brian Brown.
'91 318i

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