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Air bubble in my coolant system?

drum

drum

Diamond Member
I've got a 94 Ford Ranger 4.0 V6.

Recently after I changed the oil I popped the radiator cap to check the fluid level and topped it off. Now I don't know if it was a coincidence, but afterward anytime I drive the temp gauge goes nuts. You can tell when the thermostat initially opens, but shortly thereafter the gauge goes all the way up to hot and then immediately back down to cold.
Its pretty consistent. Could I have an air bubble in the system or is my thermostat toast?
 
Well.. If it was an air bubble i'd think that as it got circulated round the system, it would get to the resevoir and stay there. I'm not sure what it could be, maybe you have a blockage somewhere?

When you say the temperature returns back to cold do you mean normal temperature or cold as in off the gauge? If it was the thermostat i couldn't see the coolant getting cold after shooting up high, since the fluid was warm anough to open the thermostat anyway.

Try thoroughly draining the system and see if that fixes it.
 
The gauge just goes from low to high with a 'normal' stretch in the middle. When it immediately cools off after being high on the gauge, it returns to the position it would usually be at when operating correctly.
I should mention that when it first started doing this I wasn't getting any heat when I would turn the heater on, but the last few times i've driven i've had heat 😕
 
Not sure I fully understand your problem but a sticking thermostat could cause the wild temperature swings.
 
I had a very similar problem that persisted for a while after I had flushed my system. Someone told me to park the car on an incline (with front end up) and run the engine a bit (suggesting the air bubble problem). I also replaced the thermostat at the same time. Problem went away. I don't know which of the two solutions achieved carvana.
 
My old car did that. Found the connection to the temp sensor was loose. Tightened it down and it behaved normally again. It happened randomly too.
 
Is that the radiator cap that says Do Not Remove, and that you should add coolant to the reservoir only? 😀

Just kidding.

You could always run the car for a little while with the cap off when it's cold. That should allow an air bubble to escape when the thermostat opens. The only way an air bubble could get in, I believe, is if you have a leak somewhere.

The fact that you had no heat worries me. Makes me think "head gasket". One thing that can make your temp gauge go to full hot is a steam bubble from a leaky head gasket.

The last time I had a screwy temperature gauge on a Ford, it was the sensor. I had eliminated the possibility of the car actually overheating, since it showed no signs of it at all, other than the intermittent hot indication on the gauge, so I was left with the sensor or the gauge. I pulled the wire off the sensor and grounded it, and the gauge went to full hot, which meant the gauge was okay to me. So I changed the sensor and the problem was solved.

Overall, it does sound like a sticking thermostat, though.


 
Thanks for the suggestions. I already have another thermostat, just need to put it in. If that doesn't help i'll try the sensor. Hopefully the head isn't cracked 🙁
 
Like a poster above said, take the radiator cap off and run it up to norm operating temp. Watch for bubbles coming out of the fluid. Switch your heater on so any air is flushed out of your heater core. If your fluid drops during this, be sure to top it back off.
 
its air in the system. i changed the thermostat in my grand prix and got air in there. i have a bleeder valve on the thermostat neck. i got the car up to operating temp and then cracked the bleeder and let it trickle out. initially it spit until the air got out then trickled. took several drives around the block and bleeding to get it all out before the temp gauge finally stopped fluctuating. check for a bleeder on yours.
 
I have a Jetta with a sealed radiator. I recently had to replace the housing for the thermostat; it had a tiny cracking in it. It was ran at critical temperature. Not longer than ten minutes though. Before I was able to replace it I used bars leak. I drove it, but I had an emergency and wasn't able to let it property cool to harden. So I used another one. I finally replaced the housing. Ever ever since then, I've been experiencing issues with overheating. The temperature gauge is showing its at normal temperature, however under the hood it is smoking and much hotter than normal. It is also telling me that the oil is low, but it's not. I've changed the thermostat, the water pump. When I add coolant to the reservoir it instantly bubbles back up in an eruption. Could I still have an air pocket or could I have blown the head?
 
iandylan2330 said:
I have a Jetta with a sealed radiator. I recently had to replace the housing for the thermostat; it had a tiny cracking in it. It was ran at critical temperature. Not longer than ten minutes though. Before I was able to replace it I used bars leak. I drove it, but I had an emergency and wasn't able to let it property cool to harden. So I used another one. I finally replaced the housing. Ever ever since then, I've been experiencing issues with overheating. The temperature gauge is showing its at normal temperature, however under the hood it is smoking and much hotter than normal. It is also telling me that the oil is low, but it's not. I've changed the thermostat, the water pump. When I add coolant to the reservoir it instantly bubbles back up in an eruption. Could I still have an air pocket or could I have blown the head?
Click to expand...


Best to start a new thread.

hard to say but a trick I do on cars hard to bleed is jack the front end up, or where ever the coolant is added. Air will rise so jack that point up and run the car. It will usually burp itself and then you top off as needed.
 
It seems like your system already had air in it's system prior. I would start by properly burping your cooling system. That usually involves opening the radiator cap, topping off, leave the cap off, run the engine until warm. After it's warm, leave engine running, turn your heater to max, make sure you get heat. All the while, make sure your radiator is always full. While you're at it, you might as well buy a new radiator cap. If it's the original then it's twenty years old. Best of luck.
 
iandylan2330 said:
I have a Jetta with a sealed radiator. I recently had to replace the housing for the thermostat; it had a tiny cracking in it. It was ran at critical temperature. Not longer than ten minutes though. Before I was able to replace it I used bars leak. I drove it, but I had an emergency and wasn't able to let it property cool to harden. So I used another one. I finally replaced the housing. Ever ever since then, I've been experiencing issues with overheating. The temperature gauge is showing its at normal temperature, however under the hood it is smoking and much hotter than normal. It is also telling me that the oil is low, but it's not. I've changed the thermostat, the water pump. When I add coolant to the reservoir it instantly bubbles back up in an eruption. Could I still have an air pocket or could I have blown the head?
Click to expand...

Either the stop leak clogged your system and the coolant is boiling from lack of flow, you blew the head gasket, or both and you blew the head gasket because of the stop leak.

Outside of a seal sweller in engine oil, stop leak of any kind is BS and self sabotage. If it stops a leak then it also stops the flow of a fluid. Try and flush the block and radiator out with a hose, pray for the best.
 
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