How bad is having the temperature going above 210 and staying at 3/4 of the gauge (250?)? Any recommendations?

 

not good.
something is bad...
are you getting any check engine lights?

 

Sounds like the thermostat is sticking partially closed or not opening when it should.

 

Trailblazer thermostats are known for failing in the OPEN position--- where it over cools- and sets P0128.

It is possible that its failing in the closed position-
Have you checked your coolant?
is it clear and red?
or has it started to form muddy looking stuff?

did you mix green and red coolant?

is your water pump ok?

 

Thanks for your response. Before answering your questions I'll give you a bit more info about what is happening and since when...I think it will give you a better idea.
I have had this TB since Dec 08, it was 48Kmiles at that time. Now it has 54Kmiles. Last thing I had done on it was engine oil and filter change, added some brake fuild and some green coolant (less than 1/4). Temperature was going high before this and that was the reason I had this things done. Actually temp started to go high when I was in south TX at 105-110 degrees. I tought it was normal, but now back to north TX with lower temps it keeps going at 3/4s.
I've had check engine lights only once. Last thing it did was getting stuck and not moving forward or in reverse when temp reading is 3/4. When I let it cool down everything works fine.
Please read the above info and see if anything makes sense.
Thkx.

 

well, the bad news is--- that the DEXCOOL- the pink stuff... DOES NOT mix with the regular green stuff.
These 2 dont get along and I believe it begins to form clumps of goo.
This is bad- as it can cause clogging.
Also- if you added coolant--- was it leaking?

 

I see. Actually before and after I added the green coolant there hasn't been any leaking, it was added to the refill tank and it was no more than half a quater. However, the tempature started to raise before (with only pink coolant). What would you do and in what order to try to address / fix the following issues?
1. Temperature high and almost between 1/2 - 3/4 of the gage.
2. Possible issues by mixing coolants.
3. Gear stucking after temperature gets to 3/4 and working fine before it gets hot (trasmission being affected? or needing maintenance?).
4. Recommended maintenance or diagnostics from now on.

Thanks again.

 

If you mix DexCool with teh standard green coolant, it will gum up on you and become like gel. NEVER mix the two. You can put the yellow extended life into it, but nothing green.

You need to flush out your entire coolant system really good. I don't mean just a drain and fill on the radiator, you need to take it to a shop and have them throw it on a coolant machine that is ran by air pressure. This will flush out all of the gunky coolant thats been cloging up your system.

Your orignal problem was probably cause by a bad thermostat. Change it out with a low temp thermostat. I've found that low temp t-stats tend to work a little better, plus you will get heat quicker when you first start your truck during winter with a low temp t-stat