There should be a list of engines in the box with the compression tester. If your engine is on the list, then use the attachments indicated.

Google "Lisle 75500". Pretty reliable tester for showing exhaust gases in the coolant. An acquaintance of mine, who supervises a fleet repair shop, swears by this kit. A positive result indicates a problem. A negative result indicates no exhaust gas leak with 90% accuracy.

Normal running temp should be 80-90C. If you get hotter than that just idling, then you are too hot. If you get up to 80 from dead cold in a minute or so, then you just might have a bad head gasket or worse.

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'79 240D