fuzzy, popping extrusions , but only close to bed

Hello, i think i have a problem with one out of 5 printers i regularly use, but the problem is a bit dodgy. it only manifests when i print slow with big nozzles.
I made a model of a christmass ornament ball, Sliced it for 0,8mm nozzle mostly a vase mode but top part is regular 3 layers cap due to overhangs
It prints fine on 3 printers but on the modyfied ender 3 i own it behaves as if every filement was wet for the first 15 milimeters of height and then clars up.
I have no idea what is going on because it prints the whole rest of the mopdel even better than the other printers especially the top part, but on the bottom, poping noises, stringing very rough finish and ocasional small pinholes or straiht up random holes.
But it always always clears up the longer it prints or faster (130% speed of the same file and up).
i am using the same gcode on my homemade printer, work owned ender 3 s1 and some creality white cube with chaimbor modyfied by x3d, and my ender 3 at home
i even used the same spool of filement, i tryed pla and abs, dry and wet
and even though on freshly dryed pla or abs the artifacting is smaller, it always persists in the same area of the print stacked 0,1mm layers at 45 degree angle but only on the bottom

failing multicolored print was just a straw that broke camel's back

i need to figure out what is going on with the hotend in my printer because i pretty much certain it is something silly like bad thermistor contact
ender 3 is running stock creality hotend it came with, but so is my homemade printer although i regularly swap heat blocks to new ones when i break the threads

... could be "overheating" in combination with a heated bed ...

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

PLA temperature was set to 215 C, ABS 235 C , with some filements at work like white , black or silver pla i need to rise it to 225 or the layers don't stick.
Bed is at 60C for black plastic surfaces, and 75 if i print on pei

Temperature on screen is displayed in a range of 1 degree of the target. but who knows what it really is. I replaced thermistor one day because it was breaking up and run the runaway alarm on 1 out of every 3 prints, when printer lost reading for the nozzle.

It is really puzzeling actually because at work i printed this exact model using pla that was open for 2 years, and just sat in the basement all this time without box. and also with pla that ccame with chinese 3d pensin a ziplog bag with no dehumidifier at all. in both cases i had no issues, but it was printing on a creality hotend i never took apart more than the nozzle.

I think i have solved it, thanks to reading VDX comment along with the stuff i wrote and adding the two together. It was in fact overheating, by consistant amount ~20-25 degree. for the silly reason.

I filled in the thermistor hole with cheap white thermal paste and pop it back in, and the prints become normal, surprisingly identical to the ones at work or my homemade printer.
Silly thing being they are also a little more satin on top and struggle the exact the same way on the top layers as all the other printers, so i raised the temperature of print to see when it would look the same as the one with artifacts on the bottom.
i ended up determining that pla printed above 235 degree C instead of set 215 because that is when poping start and the top clears up

i guess replacing mare metal thermistor to glass bead style is harder than i thought and it was olnly sensing heat by convection or something.

thanks for atention and help

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]