thermostat housing

[forcenine]

Members and DOn,
To solve an overheating problem on my long-sitting A4, I opened up my thermostat housing to evaluate/replace the thermostat and discovered, to my horror, no thermostat and an interior resembling the aftermath of a lava flow. See picture. My question is, does the inside serve as a cup to hold the water and therefore not have any passage holes in the bottom? (other than the two hoses leading raw water in and out.) I'd like to pour in oxalic acid and leave it there for a while before trying to break up the deposits but want to know if somehow it will leak out into the block.

I've never seen a normal housing--top and cup. If anyone has a pic of such, it would be very useful. Thank.
Lisa (forcenine)

[Allen Kamfonik]

thermostat housing

Lisa,
I have just finished rebuilding my A4 and may be able to shed some light on your motor issues. The cup you are referring to is the motor head. The head has passages to allow water to flow and cool the engine. This water flow works with the thermostat and the upper housing. The thermostat is part of a valve system so when the engine comes up to temperature it opens and seals off the input line to the housing allowing cooling water to flow through the block head and out through the manifold. Without the thermostat you don't have the correct flow. When I removed the head from my motor half of the holes that allow the cooling water to flow had been blocked by rust and deposits. You may have the same issues. Good luck, Allen

[Don Moyer]

Hi Lisa,

I'm attaching a photo comparison of the underside of an old and new thermostat housing.

Only time will tell, but I suspect that when you start chipping away inside the housing at the port where the bypassing water enters, you'll find that there will not be a functional shape remaining there for the thermostat to close off when it fully opens at around 180 degrees. If that turns out to be the case, you would probably better served to consider our aftermarket thermostat kit, since you will at that time have neither a thermostat nor a functional thermostat housing.

On a positive note, it looks like the top of the head (where the thermostat housing seats) will clean up nicely by simply scraping with an old wood chisel or putty knife. I wouldn't worry too much over the apparent "lava flow" inside the head for now, although when you get everything put back together, your engine would probably benefit from an acid flush (I'm attaching the instructions for that process as well).

Don

[Dave Goldsmith]

Thermostat housing

Don:
Regarding your procedure for "acid flushing", what is the "downside" of doing the muriatic acid flush WITHOUT removing the thermostat, but just clamping off
the hose?
Does the muriatic acid attack and destroy the thermostat??
I installed your "oil checking" tube, love it, but the downside is I have to
remove it to take off the thermostat housing, a "non-loveable" job.

Dave Goldsmith

[Don Moyer]

Dave,

It shouldn't hurt the thermostat, but it will take a lot longer to draw the acid solution in through the engine.

Don

[williamg]

great new thermostat

I installed the new MMI thermostat with spacer as well as returned the hoses to the proper configuration. Now the engine comes up to 160 on the gauge and stays there. Wonderful feeling.
Bill