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1988 Mazda B2200 Engine timing issue

Hi, I have been stumped by this problem. The engine “pings” shortly after I get in and drive it when the car is warming up. I watch the engine temp rise…and when it starts to get warm just before the thermostat opens and the temp drops the car “ping or pre-detonate” when the accelerator is gently pressed. After the engine warms up… no problems. I drove it from Port Angeles Wa to southern Oregon with out it ever happening… but when I drive a short distance to town it consistently happens. I have checked what I know how to but beyond that it seems odd. Its it normal for the engine temp to rise up warmer than the normal operating temp, and then drop back down? The thermostat was recently replaced. It seems something is creating excess vacuum
during the warmup time that makes the engine ping. All the vacuum gizmos and gadgets make me crazy…

There is a problem with “it is normal for the engine temp to rise up warmer than normal temp, then drop down.” That should not be normal. Remove the thermostat and confirm that it is installed with the spring/pellet down and if there is no bleed hole in the outer ring drill one there. Your description is indicative of a seeping head gasket.