2005 Envoy intermittent overheating

[ThaSatelliteGuy]

OK... When I bought this Envoy, it had a destroyed water pump and a bad fan clutch. (bearing was obviously fubar) The person had tried to take it apart, and failed, so they sold it cheap. I bought a water pump from Oreilly and a fan clutch online. Also had to do a couple other things like front wheel bearing and clean the VCT solonoid, but other than that runs good. I noticed that it was running cold, about 150. Then it'd run around 210, then once in a while, it'd overheat. Whenever it did, it'd be low on water. I spent about a month thinking I had a leak I couldn't find, because it'd only do it once in a while. I replaced the thermostat, and now it runs 210 or overheats. I have noticed a pattern of highway driving, then slowdown = overheat. However, yesterday, it started overheating on me when still on the freeway, so it's getting progressively worse. It is also getting progressively warmer here in south Texas too, so...ya. Here's what I know:

1. It runs 210 or overheats. No in between.
2. It IS overheating cuz it's boiling off water into the overflow like crazy.
3. It will go all the way to 260 (Had it go far enough to chime at me once)
4. When it does decide to overheat, the temp shoots up very quickly. 5 minutes tops.
5. Fan appears to be working as designed. I even bypassed the solid state relay once to effectively put it at 100% duty cycle, and it starts the fan roaring as it should.
6. I am fairly positive I have a coolant flow issue, as I pulled in to the drive yesterday with it starting to overheat again, and let it idle and let the temp rise. I put the water hose on the radiator (very cool water too) and it basically didn't even slow it down. Straight cold water flow on the radiator should have arrested an overheat instantly if it was an air-flow issue.
7. Even though the water has always been ridiculously clean, I just removed and disassembled the radiator, and to my dismay, found what I expected... nothing. Clean like new.

The only other thing I can mention is, when it has gotten it hottest, I hear a buzzing sound coming from the left side of the engine for a short time as it cools down. Almost like the thermostat is squeezing water thru. However, the thermostat is brand new, and it did it before on the old thermostat too, the old one just stayed open and ran it at 145-150 most the time. I'm baffled....

 

[Tiggerr]

Only thing I can think of other than something really bad (head gasket or cracked head) would be the impeller on the water pump cavitating and not pumping properly due to bad bearing or faulty impeller/shaft... something..

Remote possibility the radiator cap holding too much pressure...

 

[ThaSatelliteGuy]

Ok... Been doing more reading....lol Could it be clogged cat causing this? I forgot to mention, when I bought this truck, it had a mysteriously blown out doughnut gasket, which I have replaced. I have a laser thermometer, can anyone tell me what temp it should run, and what temp is a problem? Also, it looks as if the cat has been replaced sometime in the past, but I can't tell when. (182k on the clock)

 

[mrrsm]

Not a Clogged Cat... but perhaps a Clogged Heater Core...which essentially shares the same dynamic flow of the Coolant that services the Aluminum Engine Block and Radiator in an endless cycle.... naturally propelled along by the Water Pump. There are quite a few prior posts that will instruct you in how to do this... but cleaning, purging and blowing out the Crap lodged inside of the Heater Core and changing the Coolant for a new batch of the Orange OEM stuff could solve this problem.

Please look closely at the image of this '2002 ONLY' item (Your Profile shows your Birth Year instead of the Year of the Envoy) as you can see that it has a pair of In-OUT Pipes that feed through the Engine Firewall that can be isolated and fitted with "Flush In -Flush Out" hosing clamped in place to accomplish this task without necessarily having to R&R the Heater Core.

DO NOT INTRODUCE ANY CHEMICAL FLUSHES INTO THE ENGINE BLOCK OR RADIATOR AS THEY CAN CAUSE THE ALUMINUM TO DISSOLVE FROM THE INSIDE OUT AND RUIN THE ENGINE:

https://www.amazon.com/dp/B00A3NT0Q4/?tag=gmtnation-20

 

[ThaSatelliteGuy]

Sorry, 2005 was in the post title.. And no, I doubt very much that it's a "clogged" anything in the coolant system, as the radiator had NO trash, and ever since I've had it, there has never been ANY indication of rust or stop-leak or anything of the sort. Since I have the radiator and shroud out, I'm considering pulling the water pump and taking a peek, as well as thinking about pulling the thermostat temporarily to see what happens, since this one can be removed from the housing without damaging anything...

 

[Mooseman]

I'm thinking maybe you got a bad thermostat? What brand did you use? Did you also replace the coolant temp sensor? Although you're obviously overheating, it is a high failure part and the heat probably hasn't helped it and usually recommend that it be replaced at the same time as the thermostat due to its location.

A plugged cat is also a possibility but you would have other issues like low power and bad MPG. You could test that theory by removing the O2 sensor and see if it improves.

 

[ThaSatelliteGuy]

I am fairly certain it's the thermostat now. I gutted it and put the radiator back in with no fan and just filled it with water and waited for it to go past temp. Then at about 230, I put the water hose to it and the temp dropped like a turd in a well. Now I'm going to pull the radiator and redo my extremely poor tank reassembly...lol Then put it all back together and run it for a few days and see what happens. I also noticed that even at 230, both hoses were soft as opposed to hard before, and I could see a LOT of flow in the top of the radiator, which I didn't see before,even while burping... Damn chinese ebay parts....