04 trailblazer overheating

Asked by Cbrooks52 Jun 12, 2020 at 02:30 PM about the 2004 Chevrolet Trailblazer LS 4WD

Question type: Maintenance & Repair

Ok a few days ago I notice my trailblazer was
running a little hot. I found a leak around the
water pump and replaced it. I flushed the
radiator and removed any air bubbles, checked
for leaks and bad hoses. I fixed all visible
problems. It still ran hot (not all the way in the
red zone. About 215 degrees). I then removed
the fan just incase and replaced it with a high
performance fan. Went down the road and
again, it ran hot after about 15 minutes. I
removed the thermostat and tried again. And
again't, it ran hot. Next I bypassed the heater
core, removed all air bubbles, checked the
hoses again, checked for a faulty water pump,
put high millage coolant and purple ice in the
radiator. And it ran hot again . I've had the
head gasket checked, oil level checked,
transmission fluid checked. I have no dang
clue what to do next! It cools off when I'm in
motion but as soon as I stop at a red light the
temp creeps back up. It seems to get hotter,
faster when I have the brake pressed at a
stop. It still runs hot in (P) but not as quick as
it does when it's in (D) at a stand still... And Im
sure the Guage isn't faulty because it bubbles
and boils out of the reservoir. I'm lost!
04 trailblazer LS 4WD
200,000 miles

5 Answers


How old is radiator and any check engine lights for coolant temp sensor. Sounds like you need fans coming on earlier which equals coolant temp sensor issue.

The radiator is few years old. We checked it out. We even cleaned all dust and debris off of it. The fan is wired to a switch inside the cab, it gets turned on immediately. It's so hot here in georgia, it just takes about 5 minutes for the truck to heat up to proper temp. The check engine light is on but it's because of a coil pack we recently replaced.


Have you pressure tested cooling system. Hold pressure 1 hour? Read pressure recommendations for your vehicle on radiator cap.


I just caught something in your post...bubbling in the coolant reservoir is a sign of a blown head gasket. Recheck this. There are cheap chemical testers on amazon that will tell you if you have a blown head gasket. Basically combustion gases in coolant.


Have you checked the real temperature with scanner? Should be around what your thermostat rating is. Our gauges are horrible, don't trust them. Good news, in 04, the temp sensor is right above the t-stat, cake job.

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