Based on field tests carried out between 1991 and 1995, a retrofit
package of modifications was introduced for Sulzer RLB90 engines in
1993 and for RLB66 engines in 1995. The main element is the change
to loop-cooling in the cylinder liners, an improved cooling technique
that reduces the thermal and mechanical stresses in the top collar of
the liner (Figure 12.46). By optimizing the running surface temperature,
the system also reduces corrosive wear and extends the time-between-
overhauls up to two years.