Not much point in checking the engine when it is warm if you are concerned with cold starts. It is a handy comparison aid when you are checking the over-all health of the engine regarding wear.

At 300+ PSI your problem isn't with compression. 275 is considered "minimal". I suggest you borrow another compression gauge to verify the results. I've had gauges lie to me before.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
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