Coolant temp above normal at higher RPMs

I have an interesting problem with my 04 aveo. The coolant temp gage normally stays just under the half mark. Now it climbs when the engine is under heavy load such as climbing a steep hill or running at or above 2500 rpms. At idle or driving slowly it stays where it should. The car has 202000 miles. I have previously replaced the oil pump (went out a few years ago), water pump (with the oil pump because I was there), oil sending unit, water pump again along with having the head decked (no valve work just resurfaced),and thermostat. The car ran flawlessly after I had the head resurfaced. Had a coolant hose burst. replaced that and the radiator, now I'm having this issue. I'm not sure what could be causing this. I'm thinking maybe the thermostat or the head.
Anyone have a similar problem? Any ideas or thoughts greatly appreciated.

Is it losing coolant? Do the coolant and oil look ok (no mixing)? Unusual to have a coolant hose burst, due to how tough they're built these days. Could there have been a major overheat which caused that hose to burst? Did it ever run without the gauge going over half, after the hose and rad were replaced?

How much higher is it? how much did the head get decked? increased compression will cause higher temperatures.

Did you burp the system with the work you have done? turn the heater on full blast while filling/burping the system?

It doesn't appear to be losing any coolant. The coolant and oil both look good. The temp was normal after I had the head decked, although the guy at the machine shop said he had to take a lot of material off to get it true. It was good for maybe a year or so. I didn't have any cooling problems till after the coolant hose burst and it got hot. I did burp the system after I repaired the hose. I have ordered a new thermostat and seal from RockAuto. The local parts houses here cant get the thermostat seal that gets sandwitched in the 2 part metal housing. All they can get is the O ring.
I'm hoping that maybe the thermostat went kaput when the hose blew. I'm relying on the dash gage for my temp info. Not sure how accurate that is. /sigh When driving slow keeping the rpms around 2k the temp stays just under the half mark which is where it normally stays. when I run it 2500 to 3000 like driving highway speed or when going up a steep incline ( I live in eastern Ky) the temp gage climbs up to 3/4 mark at which point I pull over for a few minutes till it returns to normal. I'll try reburping it. It is possible that I didn't get all the air out.
Thanks for the quick replys.

Hi.. I have 2005 Aveo Hatchback LS and I live in south Texas where the temp here usually 105F and 102F in the shade. My temp gauge maybe goes one line above the middle but never beyond that. If the thermostat gave out it should fault open meaning the thermostat stays open. So on cold winter days the car would take longer for the heater to be warm. Have you checked your fan? I would also check the relays as well and fuses. If fuses checks out then check the relays. You should have 2 of them, one for low speed and another for high speed. One the low speed there is a resister located on the driver side below the battery between the headlight mounted to the vehicle. Resistor is made of ceramic with a red wire on each end. I've heard that these fail or break and fall apart. If it is just replace it. Let me know if you need to find out the part number for that if you need it.

I just went through this issue. you have a bad t-stat. get that guy replaced.

I have one on the way. wanted to try this as a last ditch effort before I shelled out for a remanned head. I'll let y'all know how it works out in a few days when I get my parts.

thanks for the replies y'all.

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Originally Posted by xintersecty

I just went through this issue. you have a bad t-stat. get that guy replaced.

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I too just had this issue. I replaced with a new on from eBay. $9.00; shipping including The OEM plastic one was replaced with a 2-piece cast one about 6 or so years back when it broke suddenly. The replacement was a 2-piece cast one too. I got the new O-ring gasket from Autozone. Additionally and frankly, I don't see anything wrong with the bad one.

I knew it was performing better right off the bat; the temp gauge now stays a little under 1/2 no matter how big the hill is. I took it on the few interstate hills that I have around the house and temp gauge still a little under 1/2. I even made it downshift on the hill ... it still at < 1/2.

chuck