Cleaning Heater Valves
As of:  15 January 2003 

In the latest edition of "Brit Bits", the monthly  newsletter of my local club, the North Alabama British Motoring Society, one of our members - Mark Reavis - wrote a tech tip that's appropriate for this time of year.  It was so neat that I decided to include it in our Weimer-ology section.  Hey, it fits the intent of Weimer-ology!  Thanks, Mark!

by Mark Reavis

        Refuse to let Winterís grasp keep you out of your LBC this year?

        Canít get your heater to, well, heat?

        Flushed your heater and cooling system Ďtil youíre blue in the face?

        Still freezing?

        Big money says your heater problem is the valve on the engine that opens to let water into your heater.  These little valves seem to be common to most BMC/BL cars, but especially on MGBs and MGAs.  And equally troublesome is unbolting the valve from the head.  There just isnít enough room to get a wrench in there and rotate it too.

The easy way to fix it without removing the valve assembly is to: (But first, drain about a gallon of antifreeze out of the radiator.  And always work on a cool engine!)

1.  Locate the pop rivet that holds the two halves of the valve together.

 Reavis1.jpg (46051 bytes) 2.  Drill out the rivet with a 1/8" bit.

3.  Rotate the valve body slightly until it disengages from the part of the valve still bolted onto the block.

4.  Pull back the disengaged half of the valve.

 Reavis2.jpg (46836 bytes) Now you should see the orifice on the block clogged with a white paste.  You can twizzle (is twizzle a word?) this out with a probe or a drill bit. When you're finished, reassemble the valve and put in a fresh pop rivet.

     The whole process should take less than an hour.  I've done it more than once, so it's a common enough problem and easy to fix.  The problem comes when someone who doesn't know about this starts messing around, and flushes or replaces everything in the system but the valve.  Things get expensive then.  Iíve even seen people write in stating that the hole in their head was never drilled out at the factory, when it was just completely clogged!  In the worst case, your head may need to be hot-tanked.

     These valves are always marginal at best.  They are also one of the only aluminum parts on a cast iron engine, and the electrolysis reaction causes the paste to form when 1. the antifreeze mixture is weak, and 2. the chassis ground is marginal. The heater control cable can be a secondary ground if the engine - to - frame ground strap is loose.

        And speaking of the heater control cable, before you even start this procedure, ensure that you are getting full travel between the control knob and the valve.  It has to open properly to work.

     The heater core is usually a nearly bulletproof unit with ample internal passages.  I found the nearly 40-year old core on my MGA to be fine, so unless it is leaking, it's probably not the problem.

        (theAutoist NOTE:  &, if you want to modify your control valve for even more water flow, click here to go to Bob Muenchausen's site.)