OT: Automotive Cooling System Anomaly, Critique My Diagnosis

dbCooper · April 25

Back home from taking the old 2006 Impala SS on a road trip to Colorado last week. All went smoothly except for a single incident during one of our days in RMNP. Drove to Bear Lake (elev ~9400 ft.) for a day of hiking. Parked and used the restrooms then returned to car for our gear. Hear a gurgling sound from under the hood, bubbling into the radiator expansion tank is occurring. This was a cool morning in low 30's with minimal traffic. This car has experienced way more severe driving at higher altitudes and higher temperatures without showing this behavior. Some particulars:

- Temp gauge (just C to H scale, no numerical values) was reading where normally does, center of scale. Also have temp idiot light, it never illuminated.

- Antifreeze solution is fresh, less than 4000 miles on it. No leaks and level is normal.

- Connected my OBD-II bluetooth scanner and started car. Both electric cooling fans turn on at low speed, gurgling stops after about one min. Scanner shows no ECM codes set and coolant temp at 215-225 F.

The drive back to Estes Park at end of day was uneventful and all normal after several times of parking car and monitoring the expansion tank.

My conclusion (without facts) was the pressure relief spring in the radiator cap has weakened over the years. That combined with the altitude allowed for a lowered boiling point in the cooling fluid. The next day I replaced the cap with one made by Murray from O'Reilly auto parts, only compatible one I could find in Estes. No more issues since, but I am replacing that Murray cap with a AC Delco unit today.

Very weird occurrence in my mind and led to some anxiety until we got home. If anyone has insights for this beyond the radiator cap I'd like to hear them.

GrateEggspectations · April 25

He’s not around much anymore (no shade!), but I’d be tagging @nolaegghead on this.

I am of no help, but will be curious to see the opinions of others.

Canugghead · April 25

No help here either, but found this

Image: https://us.v-cdn.net/5017260/uploads/editor/8k/pc7919rt2zq8.png

MaskedMarvel · April 25

First thing I thought of was too much water in the coolant mix…

alaskanassasin · April 25

I’d guess the tank was doing its job, coolant was warm and expanded into the tank but not necessarily overheated.

ColtsFan · April 25

Your dx sounds accurate to me.

alaskanassasin · April 25

Or the reduced atmospheric pressure allowed the pressure release but that’s purely a guess. If the motor didn’t feel hot I wouldn’t worry about it

fishlessman · April 25

Canugghead said:

No help here either, but found this

fishlessman · April 25

dbCooper said:

Back home from taking the old 2006 Impala SS on a road trip to Colorado last week. All went smoothly except for a single incident during one of our days in RMNP. Drove to Bear Lake (elev ~9400 ft.) for a day of hiking. Parked and used the restrooms then returned to car for our gear. Hear a gurgling sound from under the hood, bubbling into the radiator expansion tank is occurring. This was a cool morning in low 30's with minimal traffic. This car has experienced way more severe driving at higher altitudes and higher temperatures without showing this behavior. Some particulars:
- Temp gauge (just C to H scale, no numerical values) was reading where normally does, center of scale. Also have temp idiot light, it never illuminated.
- Antifreeze solution is fresh, less than 4000 miles on it. No leaks and level is normal.
- Connected my OBD-II bluetooth scanner and started car. Both electric cooling fans turn on at low speed, gurgling stops after about one min. Scanner shows no ECM codes set and coolant temp at 215-225 F.
The drive back to Estes Park at end of day was uneventful and all normal after several times of parking car and monitoring the expansion tank.
My conclusion (without facts) was the pressure relief spring in the radiator cap has weakened over the years. That combined with the altitude allowed for a lowered boiling point in the cooling fluid. The next day I replaced the cap with one made by Murray from O'Reilly auto parts, only compatible one I could find in Estes. No more issues since, but I am replacing that Murray cap with a AC Delco unit today.
Very weird occurrence in my mind and led to some anxiety until we got home. If anyone has insights for this beyond the radiator cap I'd like to hear them.

With my 89 dodge the radiator needed to be filled while hot and while running to get the rest of the air out of the system. The garage had a radiator cap with a tall funnel on top to fill and run the engine. It made a real mess. You may have been airbound between the system and expansion tank for some time. Just a guess because I've never seen the fill technique before

Corv · April 26

Alaskanassassin had it, I think. "Or the reduced atmospheric pressure allowed the pressure release but that’s purely a guess. If the motor didn’t feel hot I wouldn’t worry about it."

Bear Lake is at 9,475 feet. The pressure there is around 10.3 psi, or roughly 4.4 psi (around 30%) less than at sea level.

dbCooper · April 26

I didn't put the new AC Delco cap on until today, 18 psi rated unit. That is correct for the car, same as the temporary Murray product I put on in Estes. Stored the Murray in the trunk for a spare and grabbed the "original" Delco to toss it and notice it is rated 15 psi. WTH?

In my mind this pretty well explains the issue I had. I paid a shop last Summer to do a cooling system flush. Looks like they have some explaining to do. Of note, this time last year we were at higher elevations in CO and had no issues. Seems to be the norm these days to pay craftsman rates and get laborer results, even from previously trusted sources.

lousubcap · April 26

Way to pursue the issue to the point where you are confident in the observed outcome.
Happy Friday-

alaskanassasin · April 27

If they flushed it last summer I’m with @fishlessman there might have been some air in the system that was worked loose on the incline.

OT: Automotive Cooling System Anomaly, Critique My Diagnosis

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