My '85 reads 85-90 pretty consistantly. Even then the heating was marginal so I replaced the monovalve insert. The rubber diaphram was split. Boy did that make a huge difference! Now I get more than enogh heat.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold