Freeze plug...and a bit more?

[karlw]

Was happily driving my '85 Westfalia late Thursday night when I noticed the blinking red overheat light kicking in for the first time ever.

My brother (original owner) took excellent care of the vehicle but the engine does have >120k miles on it. Guess I'm due for more surprises in the upcoming miles.

I pulled right off into a supermarket parking lot a few moments later to the sound of volumes of hissing steam & coolant draining...and decided to call it a night. (not quite the camping expedition I had in mind!) As I found out in the morning, a freeze plug had blown, shedding the contents of my radiator.

I acquired a 12mm freeze plug that closed up the hole, however I am now a bit puzzled...where the temperature guage was previously very stable (even in summer & mountain driving) at quite a few notches below the midpoint, on the 40 mile drive back home I noticed it was varying widely.

It seemed to be OK at speeds of 45-55mph, though still hotter then before (right at midpoint), and going up too much for comfort at stop lights or hills. When finally pulling into my apartment lot, with a small hill and 5mph/idle, it started climbing all the way to 75% before I could park.

Something else I noticed on the drive was that when I switched on both the front & back heater fans (on the hope that any heat drawn off the engine would be a good thing) the resulting air would cycle from very hot....to very cool air. I would turn them off for awhile and the non-fan driven airflow out the vents would return to hot again.

It *never* exhibited that behavior in its pre-freeze-plug episode days, so I know something else besides the freeze plug is now kaput.

I'm afraid I'm pretty non-mechanical, but is it possible/likely that either a thermostat and/or water pump is also blown? The coolant that I flushed out before refilling w/straight water was all very clean looking....doesn't seem like there would be any buildup/blockages from gunk.

I'm new to Seattle and haven't gotten a feel for good local VW mechanics yet, but I'll be doing that very soon....just wanted to get some ideas on some of the possible problems I might need to have checked....

Thanks to any who have time to give their thoughts!

-->Karl

[Capt. Mike]

Actually, it's probably the other way around. Something started misbehaving and caused the overheat condition that popped the freeze plug. What you're not going to like is that freeze plugs are so bullet-proof that they usually only fail if there's some corrosion or other weakness. I'd sure consider flushing the system and checking the others.

Water pumps are notoriously weak in Vanagons. So much so I stock one and it's about the only spare part I take on trips. Thermostats are normally pretty reliable, but at their cheap price, a change won't hurt.

However, your symptoms are also identical to an inoperative auxilliary cooling fan. The fan is supposed to come on with high temps and kick back out when not needed. A steady speed of 45-50 would give the radiator enough cool air, but stop & go or the slow climb up your hill would not be enough natural flow and call for the fan. Check it out first. Bentley section 19.12. (If fan is gone, see upgrade note 19.19.)

What you are experiencing may be nothing more than the usual air in the system. Dumping the coolant via freeze plug put air everywhere and the '85 isn't self-bleeding. See my thread on Coolants, clearing the muddy waters in the archives section of the TIPS forum. It has some bleeding tips.

I use Seattle as a jump-off point for our AK & NW Canada trips. University VW in Seattle (Roosevelt Way NE) has done several services and minor repairs with good results.