Bad thermostat?

[Mike534x]

Hi everyone, trying to figure out if my thermostat just went bad or the coolant temp sensor is bad.

We bought the TrailBlazer last year. It's sitting at 157K miles and we have no idea what the maintenance history is on this thing was.

To start it off (just a run down of what we did so far)

Did a complete tune up with Delco Iridiums + plugs. The previous owners took it upon themselves to do the tune up....although they botched it up somehow. We pulled out 7 NGK Iridiums and 1 Delco Platinum.....the original plug that was in the truck since it left the factory. We didn't pay attention to where it came from but I believe it may have been in cylinder 3 or 5 that sits behind the control arm in a not so friendly place to reach.

Since it was somewhat nice out, I did the front + rear differentials and transfer case. I also flushed the coolant because whatever was in the coolant reservoir wasn't the orange we all know that is Dex Cool. I jacked up the front end and pulled the radiator cap to see......something neonish....that didn't sit to well with me. I pulled the lower radiator hose and let the coolant drank into the pan and what came out can be described as orange + green in this odd brownish hue.....its hard to describe. It didn't seem like too much that came out but we flushed the system with distilled water and tried to get any air bubbles out, we put about 2 gallons worth in, which seemed more then what came out.

I had Torque open on my phone and it shows the coolant temp fluctuating between 180-195.4 F and it sits about 2 notches to the left of the 210 mark on the dashboard. Is this a normal temperature for the engine to run at? I know the I6 was between 190-210 but I'm not sure if that applies to the V8 or not. If it is the thermostat (no engine lights on) I was thinking of ordering that and the coolant sensor because I have no idea if both are shot because of the mixture of whatever coolant was in there beforehand.

 

[AWD V8]

If you simply dump the coolant and refill it at the rad you will have an air lock, and that will cause the temperature to fluctuate.

On the 5.3, fill the rad and ten loosen this hollow bolt for the steam vents, located behind the thermostat on the head.


If you have a cooling system pressure tester, just gently pump it up to increase the pressure. You will need to pinch the overflow hose to the reservoir. Once the air bubbles stop, tighten the bolt and you are bled. If you don't have a cooling system pressure tester, just start the engine and with the rad cap on it will build pressure as it warms up. When the bubbles stop, tighten the bolt. View: Looking from the top down.

Also, on my 5.3 I installed a Stant thermostat. I've used Stant for years, and only recently had some temperature fluctuations on Hondas. Installed a thermostat from the dealer and that fixed it. Well, my temps on my 5.3 were fluctuating, and I knew it was bled completely, so I installed a GM thermostat, temps are steady now.

Bleed it first, then install a dealer thermostat if the temps are not steady.

 

[Mike534x]

If you simply dump the coolant and refill it at the rad you will have an air lock, and that will cause the temperature to fluctuate.

On the 5.3, fill the rad and ten loosen this hollow bolt for the steam vents, located behind the thermostat on the head.


If you have a cooling system pressure tester, just gently pump it up to increase the pressure. You will need to pinch the overflow hose to the reservoir. Once the air bubbles stop, tighten the bolt and you are bled. If you don't have a cooling system pressure tester, just start the engine and with the rad cap on it will build pressure as it warms up. When the bubbles stop, tighten the bolt.

Also, on my 5.3 I installed a Stant thermostat. I've used Stant for years, and only recently had some temperature fluctuations on Hondas. Installed a thermostat from the dealer and that fixed it. Well, my temps on my 5.3 were fluctuating, and I knew it was bled completely, so I installed a GM thermostat, temps are steady now.

Bleed it first, then install a dealer thermostat if the temps are not steady.

Ah that could explain it. I was just going to put an Delco thermostat back in if this one is actually bad.

I'll have to try this out tomorrow, there must be some air still in the system. Went out and the truck was still a bit warm even though its been a few hours (2-3) and its pretty cool out at the moment. This was where the needle was pointing on the dash, and OBD showed about 158(?). Will report back if I can find the bolt and bleed the system.

 

[Paul Bell]

Mike534x, you're not telling us what year this truck is. Although it probably isn't bled right like AWD V8 said, the radiator fan clutch is different through the years and it could be an issue.

AWD V8, FYI, it's not a hollow bolt for the steam fittings, there's a gasket with a captured rubber o-ring in it.

 

[Mike534x]

Mike534x, you're not telling us what year this truck is. Although it probably isn't bled right like AWD V8 said, the radiator fan clutch is different through the years and it could be an issue.

AWD V8, FYI, it's not a hollow bolt for the steam fittings, there's a gasket with a captured rubber o-ring in it.

Thought I had it in my original post. Its an 05 Ext.

 

[Paul Bell]

Th '05 uses a PCM controlled fan clutch. As I and others have discovered, it's pretty troublesome. It's one more thing you need to check.

 

[Mike534x]

I'm not really having any issues with the fan clutch. Before doing the coolant change the temperature did stay a constant 195-200 F, so its making me wonder if there is still air somewhere in the system after waiting 30 mins for the bubbles to settle down in the radiator while keeping the engine revved to help speed up the process. Just seems odd that the temps seem lower then before but its fluctuating from 180 to 195F and doesn't get any higher. I'm much more familiar with the I6 then the V8 so I'm not exactly sure if this is the right temperature range the engine runs at.

 

[Mike534x]

Update:

Well I replaced the Thermostat (part number 15-11057). We had the radiator cap off and loosened the bolt for the Steam vent as shown in AWD V8's post and I'm not sure if there's a big air pocket or if there is something I missed but essentially the truck started overheating. I had Toque open and the temp climbed to 248-250 deg F and I shut it down to let it cool off, we had the blower speed at max and the temp set to 90 and all that was coming out was cool air the entire time. There was a lot of coolant bubbling out of the radiator and so now we're letting it sit the remainder of the night and try again tomorrow.

Is there a chance the replacement thermostat was bad and its not opening resulting in what happened? We're going to try swapping the old one in and see if that takes care of the issue tomorrow morning.

edit: Just adding in that the lower radiator hose does get hot.

 

[Paul Bell]

Yeah, it is scary, the most difficult vehicle I've ever had to bleed. I'd imagine it's got something to do with the up/down radiator design. My Trans Am LS engine's water pump is the same but the outlets point differently and it has a crossflow radiator and it bleeds easily.

The gauge will get up there, just keep it going and adding coolant. Wen it starts to open, the coolant will boil back out of the radiator neck.

 

[Mike534x]

Yeah, it is scary, the most difficult vehicle I've ever had to bleed. I'd imagine it's got something to do with the up/down radiator design. My Trans Am LS engine's water pump is the same but the outlets point differently and it has a crossflow radiator and it bleeds easily.

The gauge will get up there, just keep it going and adding coolant. Wen it starts to open, the coolant will boil back out of the radiator neck.

Yeah, neither my dad or I ever had trouble with bleeding a system before so this is a first. We'll see how tomorrow goes. It should be getting close to bleeding out...hopefully, we were at it for about an hour. Would jacking up the front end at all help with trying to get it bled?

I'm also assuming once the temps do climb the clutch fan should kick in? Figured it would've been roaring once it hit the 240-250 mark.

 

[Paul Bell]

Yeah, neither my dad or I ever had trouble with bleeding a system before so this is a first. We'll see how tomorrow goes. It should be getting close to bleeding out...hopefully, we were at it for about an hour. Would jacking up the front end at all help with trying to get it bled?

I'm also assuming once the temps do climb the clutch fan should kick in? Figured it would've been roaring once it hit the 240-250 mark.

I imagine nosing the truck up would help. My driveway puts it like that and I've always bleed cooling systems that way. These trucks are still krazy difficult tho.

In theory, the PCM should call for more fan speed when the engine is hotter, kicks in at a lower temp with the AC on but if the thermostat is still closed, the coolant in the radiator is still cool as it hasn't been allowed to pass through the block yet.

Ya just gotta let it get scary hot until the stat opens-then deal with scalding coolant puking out from the radiator until it all stabilizes.

 

[Mike534x]

I imagine nosing the truck up would help. My driveway puts it like that and I've always bleed cooling systems that way. These trucks are still krazy difficult tho.

In theory, the PCM should call for more fan speed when the engine is hotter, kicks in at a lower temp with the AC on but if the thermostat is still closed, the coolant in the radiator is still cool as it hasn't been allowed to pass through the block yet.

Ya just gotta let it get scary hot until the stat opens-then deal with scalding coolant puking out from the radiator until it all stabilizes.

Alright I'll report back if I have success.

Really wish this was as easy as the I6 as far as bleeding goes.

The lower hose does get hot so I'm assuming the t-stat is actually open....or so I think it is. There is steam and the like coming out of the radiator opening while the coolant is bubbling out. Still can't believe this is such a difficult process.

 

[Reprise]

Ouch. This has me worried about changing my coolant. Just got my '03 (w/ 130K on the clock,so it should have a lot of life left), and my temp runs anywhere from 1 notch to the right of the second 'large' notch, to 1 notch under the 210 mark. Actually, it only got to / close to 210 once - on the hottest day of the year (mid 90s) in extended traffic jam - and it dropped down 2 notches when I cut off the A/C and put the heater on. Most of the time, it's closer to the 2nd large notch (but never under it, unless the engine is cold).

It's surprising to me that the needle moves as much as it does - I'm used to a pretty rock solid indicator in the L4 and V6 Hondas that I've been driving (I know - they don't have V8s!)

My coolant *level* looks fine - but the coolant looks *pink* to me - not orange. It's been almost 20 years since I owned a GM (last was a '97 Grand Prix), so I've been out of touch with how GM does things these days. Coolant looks to be fairly new, although I was going to check the protection level with a bulb tester and replace it before winter - but now hearing these bleeding issues, I worry that I'll make this thing run hotter than it is now.

Paul Bell - that '71 Monte brings back memories - I had a '70 in the exact same color (not an SS). Loved that car.

 

[Paul Bell]

yeah.....maybe next year......

 

[AWD V8]

with the rad cap on

Did you have the rad cap on after you filled the rad? With no rad cap the system will not build pressure and the air will stay trapped in the engine and it will overheat.

 

[Paul Bell]

Interesting question. When the thermostat does open, the radiator level drops a good bunch. If the cap is on, how do you add coolant?

I've topped off & bleed coolant systems of millions of cars-but I'm at a loss with these trucks and I'd love to know the better or trick way to do it.

 

[Mike534x]

Did you have the rad cap on after you filled the rad? With no rad cap the system will not build pressure and the air will stay trapped in the engine and it will overheat.

How do I add coolant with the cap on? I've left it off like we usually do when we bleed a system. I did have the vent bolt removed under the throttle body so I'm not sure what else there is to do without getting the engine close to overheating.

 

[Mike534x]

Edit:Can't edit the post on my phone but the truck is jacked up and the lower hose is warm but not hot like it should be? So did I receive a faulty thermostat?

 

[Mooseman]

I'm on my phone. Hope this works. I found that this type of funnel that attaches to the radiator filler neck is awesome.

Video
https://www.youtube.com/watch?v=xYkKW0OyeUc

Makes the job spill free at least. Used it on the I6, not sure if it would help burping the V8.

 

[xavierny25]

I'm on my phone. Hope this works. I found that this type of funnel that attaches to the radiator filler neck is awesome.

Video
https://www.youtube.com/watch?v=xYkKW0OyeUc

Makes the job spill free at least. Used it on the I6, not sure if it would help burping the V8.

That's pretty cool. Going to search on where I can pick one of those up. Gonna be flushing my coolant out this weekend. Which is long over do. 123xxx miles on it.

 

[Mike534x]

That's pretty cool. Going to search on where I can pick one of those up. Gonna be flushing my coolant out this weekend. Which is long over do. 123xxx miles on it.

Since you have the I6, it should be a lot easier to bleed the system....though the t-stat is a more of a pain to get to. NAPA, O'Reily and I think Advanced/Auto Zone sell them from the quick search I did online.

Ouch. This has me worried about changing my coolant. Just got my '03 (w/ 130K on the clock,so it should have a lot of life left), and my temp runs anywhere from 1 notch to the right of the second 'large' notch, to 1 notch under the 210 mark. Actually, it only got to / close to 210 once - on the hottest day of the year (mid 90s) in extended traffic jam - and it dropped down 2 notches when I cut off the A/C and put the heater on. Most of the time, it's closer to the 2nd large notch (but never under it, unless the engine is cold).

It's surprising to me that the needle moves as much as it does - I'm used to a pretty rock solid indicator in the L4 and V6 Hondas that I've been driving (I know - they don't have V8s!)

My coolant *level* looks fine - but the coolant looks *pink* to me - not orange. It's been almost 20 years since I owned a GM (last was a '97 Grand Prix), so I've been out of touch with how GM does things these days. Coolant looks to be fairly new, although I was going to check the protection level with a bulb tester and replace it before winter - but now hearing these bleeding issues, I worry that I'll make this thing run hotter than it is now.

Paul Bell - that '71 Monte brings back memories - I had a '70 in the exact same color (not an SS). Loved that car.

Your temps sound more normal then mine were. Even before I flushed my coolant the guage would always read 2-3 marks to the left of 210, with a max temp reading of 186 F, only time it actually hit 190F was after the flush but even then it didn't seem like the T-stat was opening fully. I know if its directly on the 210 or just a hair to the right of it its fine.....though if its one thing I've learned is to always trust what the the OBD reader picks up since the guages are usually off slightly then the actual reading.

I'm on my phone. Hope this works. I found that this type of funnel that attaches to the radiator filler neck is awesome.

Video
https://www.youtube.com/watch?v=xYkKW0OyeUc

Makes the job spill free at least. Used it on the I6, not sure if it would help burping the V8.

Didn't even know they made something like this!

Definitely going to pick one up. I've got a replacement t-stat coming tomorrow morning I'm going to test out before installing this time, might not help as far as burping the system but if it helps with keeping me/engine bay from being covered in coolant I'll gladly use it.

 

[Mike534x]

Another update.

Received the new t-stat.....tested this one and it opens/closes as it should.

Pulled the first replacement out of the housing and installed the new new t-stat. Filled the radiator up with a gallon of coolant and started her up with the vent bolt off and immediately was greeted with coolant coming out (didn't happen before) and once the temps reached 180ish F I raised the idle to 2,000 RPM, still a steady flow of coolant coming from the vent however the temps climbed to 224 F and stopped there and immediately the air vents started blowing heat compared to the cool air it was before, and slowly the temp gauge came down about 3-4 degrees before tightening the vent bolt and topped off the radiator until the temps settled between a steady 203-206 F with no coolant bubbling out of the rad.

I was curious and tested out the one I originally purchased and it just wouldn't open. It was a bit surprising to see that it was defective but will take it as a lesson to test them out before tearing into everything to get it installed.

At least this is taken care of......now to figure out what's causing my poor gas mileage.