Some details, probably too many but meh.
I have a 2005 lgt, ~138k miles on the original block, og turbo replaced at ~45k miles.
I have had an overheating issue that started back in about 2018 and it is getting worse, mainly cus im driving the car more than ever, an hour commute each way to work/school and back.
My car only overheats when I'm driving slow, like in traffic, through a drive thru line, around a parking lot, stuff like that. Driving at speed or on the highway, no issues. When it goes to overheat, I will watch my temperature gauge slowly rise and it will go up to just around the red but never over, it will sit there for a second or two and then drop down to where it should be, a smidge below the middle. This would happen randomly and infrequently, so i didnt worry too much. Although I did look into it and some research and the community led me to change my thermostat and temp sensor, which I did with oem units. it worked perfectly for a couple of months until I took the car off the road for about 1.5 years and brought it back on last september. She came off because I had bought another car, not because she was overheating.
In April, the problem started again, I talked to my shop and he replaced the T-stat again, problem didnt occur anymore, thought I got a faulty T-stat when I did the replacement. Back in June of this year, on the hottest day of the year, I blew a coolant line, specifically to my turbo. I had it towed home ,replaced it and burped the system. Seemed to be fine again. Then it started happening more and more frequently. Now sometimes it would hover at the high mark for longer than it did before. I realized if the revs were high, it would drop down. Specifically, If it was high, I would drop a gear, do a pull and it would just plummet to below the middle. I had thought that was really weird, but just took it as more evidence and kept monitoring. During all of this up until the last couple of weeks, besides the intermittent overheating, the car has felt fine. Pulled strong, held boost no problems, same gas mileage, nothing else telling me something was wrong.
Some other things ive noticed are that my coolant overflow would boil over and spray coolant all over the underside of my hood. I would top it off so as to not run out, and it would blow it all out so I now keep it low in the overflow tank but still make sure there is some in there. I have checked in the tank, and seen, idk if it is steam from boiling coolant or exhaust gas, but when I smell it, it smells sweet like coolant but a slight hint of something else i cant put my finger on, could be exhaust gas. A couple of weeks ago, making a pass on the highway in 5th from 75-85, there was a stutter in the car and then it went fine, got a code for P0244, wastegate solenoid performance. That has only happened twice, mainly cus I avoided 5th gear passes under boost.
After this week, now I am worried. When I hit boost merging on to the highway, the car stuttered a bit, it overboosted slightly to ~13-14 psi from normal of 11 and the boost would flutter heavily. Then I got a CEL for P0301, cyl 1 misfire, and PFFFF and PFFFE from my accessport. Reset the codes and drove it gingerly. Then this morning, I accidently forgot, hit boost, maybe about 30% throttle at most and the same thing happened.
Some of the testing I have tried include I burped the system after I noticed it had been boiling over everywhere. I did do the coolant exhaust leak test. I did the test 4 times, and the fluid never changed colors, I believe this to be because the problem isn't constant. I even tried doing the test on the coolant overflow to see if the the vapor was steam or exhaust gas. I gave it an oil change, there was no coolant or metal or anything odd whatsoever, matter of fact the oil looked really good. I was advised to run a compression test. I tried to do it myself but didnt have the capabilities, mainly the space and time. Talked to my local shop who does most of the average car stuff for me, he said not to have him do it, have the shop who would do the repair work so I dont pay for the test twice. So the compression test hasnt been done yet.
All of the things I have thought it to be are a bad radiator?, nah coolant flows fine and is clean. I also have no shortage of heat for the aircon. Fans dont work?, nope, I hear them working all of the time, especially when the car is trying to overheat. Since I could get the temperature down with a pull, maybe the waterpump? I was thinking the higher revs would spin the pump faster and move more coolant through the system. Idk still could be a possibility. Timing belt and everything was replaced at 106k. Now that I am getting a cyl 1 misfire at boost, Im thinking there is in fact a hg leak, in cylinder 1 and the its a small one thats getting worse and the boost is causing the leak to expand thus the boost issue, i.e overboosting and fluttering.
Another thing I am worried about is since the car has gotten hot a good amount of times, but never actually overheated, could my heads have been warped? If they are warped and/or there is a hg leak, when does it make more sense to machine and fix the current engine, replace the engine entirely or junk the car?
So yeah, thats my problem, dont know whats going on and I cant get a solid answer as it doesnt seem to follow any standard failure signs. Do you guys have any insight or leads? Anything is appreciated. Thanks