Just wondering how potentially catastrophic can not getting the dipstick fully reseated after measuring the oil level be? Or the overflow cap fully tightened after checking the coolant level? My bro was telling me the oil system needs vacuum pressure to operate properly which would fail if the dipstick wasn’t fully reseated, is this true?.. and it seems pretty obvious you’d lose some coolant if the overflow cap wasn’t fully retightened, anything else to worry about?
If the oil dip stick can’t be fully seated in its tube, crankcase pressure will blow oil vapors out the tube.
It depends if the cap on the reservoir is the pressure cap.
Tester
If you aren’t having troubles with these things you might as well think about the interest rate. These things are small problems. If a dipstick has trouble going back in, most people will turn it the other way and try again. If an overflow cap has problems, they get it to work. It’s not complicated. Maybe talk to your bro about something he has experience with. You wouldn’t take jewelry advice from the vending machine guy unless he was a jeweler.
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Is this a problem for you ? I guess it must be because you had a thread in 2020 about this same seating of the dipstick .
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Simple answer, not catastrophic, just messy.
Could be catastrophic if you do not check oil or coolant level after discovering your error.
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Thanks guys, I am enlightened 
@VOLVO-V70 I apologize I checked my topic list yesterday to see if I already posted re this and missed that guy.
Not having the coolant cap tight could cause the engine to overheat, if the coolant overflow tank is pressurized. What make/model/year is this car?
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That’s a puzzler. The crankcase has a vacuum on it from the PCV system. But it’s hard to understand how a reduction of that vacuum could affect the oil pump. There’s a spring-loaded valve in the oil delivery system that causes some of the oil from the pump to return to the crankcase if the oil pressure is too high, maybe something to do with that.
I expect you already know that while driving it is a good idea to monitor the oil pressure and the coolant temperature. If you do that, then neither of those problems would be catastrophic
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@George_San_Jose1 Thx how does one check the oil pressure and temperature while driving? I’m not piloting a Ferrari here just an old bimmer (riverofwind Palo Alto)
My 50 year old Ford truck is my daily driver (best to not ask why … lol). It has both oil pressure and coolant temp gauges. As for how I do it, I just glance at them from time to time. My Corolla has a big coolant temp gauge, but no oil pressure displayed, just an oil pressure warning light. Should I ever be allowed to return to using it as my daily driver, I’ll just look at the dashboard.
@George_San_Jose1 I’ve got a coolant warning light and oil light as well … Is the engine thermometer pulling it’s value from the coolant temp?
If all you’ve got is warning light, well, accept that’s all you’ve got. Monitor both parameters by occasionally glancing at the warning lights.
If you are asking if the engine thermometer dashboard warning display is controlled by the engine coolant temperature, and it lights when coolant temp exceeds a certain temperature, seems like a pretty good chance it is.
When the driving public forgot how to read gauges, they put in warning lights instead. When I ordered my 86 Buick, to get gauges I would have had to add the $2000 digital dash. Instead I just added after market gauges for volt, temp, and oil pressure for $20. Always an option but not for $20 anymore.
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Not your exact instrument cluster but similar.
Top center: red battery light—battery or charging system problem.
red oil light— low or no oil pressure,
Bottom right gauge—coolant (engine) temperature.
Get, even if you have to buy it, an owners manual and read it.
You have a car that is very expensive to repair, performing preventative maintenance is more economical.
When I ordered my '81 Citation, I was surprised that the “full gauge package” was as cheap as it was. I don’t recall exactly, but I think that the combination of full gauges and upgraded suspension was something on the order of only $200. The only downside was that the full gauge package didn’t include a clock so I had to buy a little digital clock, which I attached to the instrument panel with velcro.
If it makes any difference my 08 650i has no coolant temp. Or oil pressure gauge, this things will show as a warning 
on the driver info display. But it does have an oil temp gauge.
My Honda had a blue light for cold motor. When it went off, motor was not cold.
Trying to remember now but the neighbor bought a new 64 bel air… it had a cold light that would go out after a few blocks. I think it was yellow. Only saw it in the winter so not sure how cold it had to be.