Oil change place indicated car low on coolant. Passed pressure test. Dealer did block test passed then next day they said did hard rev test and said it failed. No leaks, no smoke, does NOT get hot, does it sound like they are duping me or is this an issue

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Took car to oil change place. They indicated that the car was low on coolant. Does not leak or get hot. Went on 700 mile trip in 100 plus degree weather and while idling in line after 10 minutes car got warm for about 1 minute and cooled immediately as soon as I started driving. Took to radiator shop did pressure test/ passed. Took to dealer who stated they did a block test and that it passed (message was on phone). I called back and advisor tells me same story but is interrupted and tells me he will call back which is next day and then says they did hard rev test and car failed test. He did not talk about dye, he talked about bubbles on last test. I feel I am being lied to. Car does NOT get hot or warm, runs great, heater works great, no coolant in oil, no white smoke, no leaks and now I check car everyday and coolant level is staying constant. Does this sound like a problem or does it sound like I'm being tricked into getting work done. Also car had a recalled long block which was replaced 80,000 miles ago. Car has NEVER gotten hot.