How to tell if you have “burped” coolant enough? (1 Viewer)

[ace7141]

I replaced my coolant temp sensor just for PM, and I notice when I cut my truck off, my temp gauge spikes. When it is running, everything seems fine, doesn’t overheat, and runs well at a normal operating temp from what I can tell. Only when it’s cut off and parked, with key in ignition, does it spike towards hot. After some research I suspected air bubbles in my coolant, so I began a burping process this AM. But I can’t tell when it’s been burped enough - anyone have any ideas?

It seems that as I let the truck run with the radiator cap off, the coolant would slowly rise to top of radiator and slowly start to pour out. I would squeeze top radiator hose, get some bubbles, then the level of coolant would drop back down into radiator. Then slowly rise to top.

Please don’t tell me I have a head gasket that is about to go...

 

[Infinity00]

Look up heat soak, or thermal soak and see if it fits your situation. After running, getting up to temp and then shutting off, the block and every other solid metal starts thermally absorbing the heat from I assume the coolant that is no longer circulating. So the temp sensor rises...a lot. I have a mechanical secondary sensor that operates without the key on, and yes I was completely excitedly alarmed at the rise in temp after I shut it off. Since then I’ve learned it’s completely normal

 

[ace7141]

Thanks for your response, I appreciate it! That does sound like my situation, somewhat. When I crank the truck back up, the temp drops almost immediately, as the coolant starts flowing.

I took it for a drive, really opened it up while driving, and the temp actually went down.

Any ideas on the burping situation? My thoughts were I didn't burp enough, and there was an air pocket rising up around the coolant temp sensor.

 

[NeverGiveUpYota]

Personally if it was spiking while running then I’d say you have a bubble (I know this from my own experience of it happening) but the spike after being shut down is as Evil said...

 

[OSS]

The good twin is showing you the way.
There's no way any engine can overheat once the ignition is turned off. The coolant could overheat (and conceivably boil) but the metal is actually cooling as the coolant temperature is rising after shut down. The heat is created inside the combustion chamber when the gasoline burns.
What you're seeing is the lag time from the temperature of the heated metal, heating up the now stagnant coolant.
Without attempting dedicated burping exercises trying to get every last bubble out, the engine will eventually purge all the air out on its own. It just takes time. About 2 weeks of daily driving is what my 2F used to take until everything settled down.

 

[klinetime574]

Don’t assume the worst. Get the front end up in the air, like on some of those oil change ramps. Start from bone cold. Maybe leave it parked like that over night. Remove the cap. Top it off. Start the truck. Get up to operating temp while nursing that top radiator hose. Make sure both heaters are open once the thermostat opens. I’ve never had a problem filling with coolant. Just take your time.

 

[Gretsch]

Thanks for your response, I appreciate it! That does sound like my situation, somewhat. When I crank the truck back up, the temp drops almost immediately, as the coolant starts flowing.

Mine does exactly the same thing. Thought I had a cooling system air pocket too and spent days trying to 'burp' it only to discover it was working fine the entire time. Runs cool while running, which is all you are really after. If yours runs the same, then I would let it roll. As others have said, the system can burp itself over time just from a few weeks of daily driving with the overflow tank topped off. System will take what it needs and give back what it doesn't.

If you are really concerned about it, you might think about using one of these no mess cooling system burping kits so you can actually see if there are air bubbles in the cooling system or not. HTH.

 

[Willard]

@ace7141 After redoing my entire cooling system, I had the same issue with the coolant coming up then overflowing.
My initial issues was even after 1-3 weeks my coolant system was pressurized and taking the cap off lead to coolant spraying everywhere.
I noticed my overflow bottle (after clearing blockage) was filling up way to much. New OEM cap did not result in a change

What I did is just let it overflow (into a catch basin) and then kept squeezing the top hose until I was satisfied there were no bubbles.
Eventually it did not overflow anymore. I added coolant as needed and let it run with the cap off for about 15-20 minutes after the coolant was at the correct level and not overflowing anymore. I then put the cap on and checked for any pressure leaks and kept an eye on the temperature for the next hour at idle in my Garage (it was 90* out so a solid test). No issues and off for a drive.
Still no issues. Let it cool and checked the coolant level, All good.
What I believe is the system was overfilled and had bubbles in it. The back pressure (even after the T-Stat was open) was pushing the coolant out of the system in the only place there it could. Keep squeezing the upper hose until you see zero bubbles and the coolant is stable.

As an FYI, this is how I actually learned how to bleed a coolant system many years ago. I am sure there are better ways but this has always worked for me.

 

[ace7141]

You all are the best, I appreciate the input!

I am resting a little more easy now. After a good burping session, I have less pressure in the coolant system. I too, think that I over filled it after performing some work on my truck. This was causing a bit of a small leak in a few loose hoses (but helped me identify what hoses were loose, and those clamps got tightened right up). I haven't had any overflow issues, and have been keeping it about 1/3 full, as needed.

After learning about thermal soak, I am certain this is the cause of the temp gauge spike after shut down, and feel much better about that as well.

I do jump to the worst conclusions sometimes But I just love and appreciate this truck! It's taught me so much. Before I got this truck, I didn't even change my own oil.. I've since replaced the manifold gasket, fully desmogged, performed a valve lash adjustment, learned how to tune a Weber carb, and do in fact change my own oil now, LOL.

Thanks again! Until the next time, when I have a problem/question and come calling to the cruiserhead hive mind.

Best Regards