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FAQ new

Chapter 21.0 Engine Problems

Subject: early twin cam fours and their coolant leaks
Posted by Jim Newman, neji@domain.elided

According to both an independent BMW repair place and a dealer here in
Monterey (CA), early twin cam 1.8 liter fours, as in 1991-1992 US 318i
and 318is models, have a propensity for losing their coolant
catastrophically from between the head and the block.

As described to me, there is an O-ring that seals a coolant port from
the block into the head, forward end.  Normally would be within the
head gasket, but for some reason they used an O-ring.  Corrosion in
the head's aluminum, under the O-ring seat, can eventually allow
coolant to get by the O-ring, resulting, naturally, in loss of
coolant.  The BMW dealer says to expect it every 50k miles!  It may be
visible as a trickle off the right front side of the engine before
things get too far along, but it sounds like most people find out
about it the hard way.

BMW changed the design in 1993 to fix this, according to the local
dealer.  And apparently BMW NA will pay part of the cost of the
repair.

The cure is to remove the head, fill in the corroded part with epoxy
goop, clean it up and put it back together.  $700 at both the dealer
and the independent shop where I learned most of this.  This should
make recurrence less likely (less metal exposed to rot away), but it's
not a guaranteed permanent fix.

The best prevention is to make sure coolant is changed regularly,
which keeps down the acidity of the coolant, and thus the rate of
corrosion.  I've heard of well maintained examples of this engine
going 100k miles with no trouble.  

Jim Newman
'91 318is