Maxcusick

Ok so my car has new radiator new cap no thermostat because it was over heating. Owner prior to me put some bs in radiator to try fix it's leak didn't work got new one. Now car over heats after and only after I get on highway for at least 15 mins above 3k rpm then it starts to over heat I get off high turn heater on still the same turn car completely off then back on then temp starts to drop goes to normal and all is fine until I get back on highway and keep above 3k rpm. I put coolant system pump and held 20 psi no drops no leaks on system and both fans work fine. Things I haven't check is psi in each piston and haven't changed water pump. I flushed coolant system ran full bottle of flush for 2 days and hooked garden hose up to heater core through the block and radiator no problems at either place. Im lost it's a d16y8

TomCat39

The likely fix is to pull the head off the car, check it for flatness and clean any goop on the cylinder wall side of the water jacket.

If the previous owner had a leak, chances are they overheated it and warped the head.

Also, there is a chance the water jacket has mineral deposits if anything other than distilled water was used. I believe that stop leak goop can and does attach itself to those deposits creating potential hotspots on the cylinders due to no coolant contact.

No fun for you.

Maxcusick

Well I looked at radiator again cuz it can't be head I did exhaust gas test on coolant and it's fine it help 20 psi on pressure test so I took my infared thermometer and when it over heated the top was 210-220 on the black tank and down on bottom between fan blades I got 140 so that's big difference im going hope the 100 just spent on radiator will fix it I don't see it having a 60 degree difference and it not being the problem and if it's not it then yea head comes off