Bubbles in Coolant overflow

I know it could be head gasket, but I'm not seeing any coolant in oil or any mustard in oil cap. There is also no white smoke coming out of the exhaust or moisture in the tailpipe. I noticed it when I turned off the car after sitting in the parking spot for a little bit. When driving around, the temp gauge had stayed around 11 o'clock, but once it sat still for a bit it rose to about 1 o'clock. I just replaced the thermostat the other day. While installing the TS I did, what I thought to be, a thorough bleed of the system, but maybe I missed a bunch of air? Im hoping its a bad hose or something easy

Its also a pretty hot day here in TN – 90s. Any advice is welcome!

p.s. I'm new to this forum and I'm not super experienced with cars, but I am open to new things and I love learning!

Welcome to TRS

With the new designs and new gasket material used coolant in the oil doesn't happen much any more when head gasket blows or head cracks

Just a quick what happens with bad cylinder seal(blown head gasket)
A cylinder has 150psi air pressure inside when cranking, i.e. compression test
900+psi when a cylinder fires, thats what pushes the piston down and adds power to the crank

The cylinders get very hot so they are surrounded with cooling passages, in the block and in the heads.
Head gaskets have a metal ring for each cylinder, when head is torqued down this metal ring is crushed and seals the head part of the cylinder to the block part.

A blown head gasket means that metal ring has failed, part of it has been eaten away, or if engine is EVER overheated, then head metal expands too much and crushes the metal ring making it fail.
After metal ring fails the gasket material can't hold the 900psi pressure back and it starts to eat it away
And it will usually eat it away until it comes to a cooling passage, sometimes an oil passage(which is where you get coolant in the oil).

Cooling system runs at 0 to 16psi pressure
So when 900psi shows up, lol, well "air" from inside the cylinder is pumped into cooling system, this displaces the coolant and causes a hot spot until the "air" is pushed out by water pump circulation
The "air" will make its way to a high spot, top of rad or heater hoses

Rad cap is rated at 14-16psi, as pressure in cooling system builds up cap will open and push coolant out first into overflow tank, cause it to be very full, overflowing sometimes.
When the "air" get there then air will be pushed out and bubble up in the overflow

But here's the thing, this will happen when engine is cold, just started, pressure build up is instant if there is a cylinder leak.
It causes overheating because it pushes out coolant from the system, and air doesn't cool as well as liquid.

Cold engine, remove rad cap, top up coolant, start engine
If coolant start to flow out of rad cap then yes, there is a blown head gasket, it is pushing coolant out
A little will come out by water pump displacement, you will know the difference, it isn't a little with bad head gasket

White smoke on start up is because some coolant will leak into that cylinder after engine cools down, some can also be sucked in on the intake stroke, making the spark plug in that cylinder look "steam cleaned", because it was

I don't think you have a blown head gasket

Bubbling overflow tank, with normal level, could be caused by a leak, loss of coolant replaced with air
Or a hot spot in the engine after shut down
When you shut off an engine you shut off the water pump so no circulation.
Engine gets hotter at that time, if you turn key back on you can often see that, temp gauge rising, totally normal, but......................
If there is a hot spot then coolant at that spot can turn to vapor, steam, this creates higher pressure and "air", which will bubble up in the overflow.

Thank you very much for the informative reply! From searching online, I had kinda come to the same conclusion, but you laid it out in a very easy way to understand! Thank you very much. This may sound silly, but is there any way to prevent this or is it "normal" and I shouldn't really worry about it? How can I find the leak where air is getting in(if thats the problem)? I recently got this truck, and I absolutely love it! I live in an apartment complex, so doing work on it in the parking lot is less than ideal, but I am not above it lol(I did the thermostat in the parking lot haha) As mentioned, I am a bit of a noob, but I think I'm a quick study and if a job is possible with basic tools, I feel comfortable doing it myself

Most auto parts or tool rental places will rent a cooling system pressure tester

It just a Rad cap fitting with a pressure gauge and hand pump

Cold engine
Top up coolant if low
Put on tester and pump it up to 20psi
Watch gauge, it shouldn't drop, should hold pressure, basically forever.
If pressure is dropping there is a leak
Since engine is cold it won't evaporate or "burn off" so you should be able to locate it easily

If pressure is dropping don't forget to check in the passenger side of cab where heater core is, they can leak coolant as well.


One other place that can Suck air in, is the overflow tank hose
Rad caps have TWO valves
Larger valve holds pressure IN the radiator, opens at 14psi and lets hot coolant flow out to overflow tank
Smaller center valve SUCKS coolant back in from overflow tank as engine cools down.
Both use the overflow hose

Air is much easier to "suck" than coolant, if there is even a pin hole leak in overflow hose rad will suck air back in instead of coolant.
So each time you warm up and cool down the engine you get air sucked in instead of coolant

Very interesting! I will swing by the store tomorrow and see if I can get my hands on a pressure tester! Sounds pretty straight forward! Ill let you know the results! Thank you so much for all the help!

RonD, Really like the way you explained that. Already knew what you described, but that's the best I've ever heard it explained.

RonD said:

With the new designs and new gasket material used coolant in the oil doesn't happen much any more when head gasket blows or head cracks

Click to expand...

I can vouch for that, blown head gasket 4-5 times on my 99's 4.0L. Each time failed between cylinder and water jacket. Never once had signs of coolant in the oil. Usually first sign of a head gasket problem on mine is a missfire.

RonD said:

A blown head gasket means that metal ring has failed, part of it has been eaten away, or if engine is EVER overheated, then head metal expands too much and crushes the metal ring making it fail.
After metal ring fails the gasket material can't hold the 900psi pressure back and it starts to eat it away
And it will usually eat it away until it comes to a cooling passage, sometimes an oil passage(which is where you get coolant in the oil).

Click to expand...

Just wish I could figure out what is making that metal ring fail on my truck. Last time I took it down to bare block and had everything inspected by machine shop, they found nothing wrong. 20K miles later it's failed again and I know for a fact it hasn't over heated.

JoshT said:

RonD, Really like the way you explained that. Already knew what you described, but that's the best I've ever heard it explained.



I can vouch for that, blown head gasket 4-5 times on my 99's 4.0L. Each time failed between cylinder and water jacket. Never once had signs of coolant in the oil. Usually first sign of a head gasket problem on mine is a missfire.



Just wish I could figure out what is making that metal ring fail on my truck. Last time I took it down to bare block and had everything inspected by machine shop, they found nothing wrong. 20K miles later it's failed again and I know for a fact it hasn't over heated.

Click to expand...

Thanks

Hopefully there is no "next time" for your 4.0l OHV head gasket, but..........if there is, do the Glove Test to ID which cylinder(or cylinders) is "blown"
Then inspect that metal ring for how it was damaged.
The ring is a softer metal and is easily "eaten away" by pinging, doesn't have to be noticeable pinging, i.e. when accelerating, just a light pinging every now and then.
Pitting in the metal ring is a sign of that.

You can "feel" if the metal ring has been crushed unevenly just by pinching it between your fingers and running them around the ring, you will "feel" where it deforms, should be nice and even all the way around.
If it "feels" thicker at one spot then, if heads were milled, the block has a deformity.

Old head gaskets can tell you alot

Unfortunately, that 20K miles later is whats happening now. I think it was back in June and probably closer to 22K that the misfire started this time. Started getting a noticable missfire and I was pretty sure of the culprit from previous times. Finally threw a cylinder 1 misfire code IIRC, so after being pissed and letting the truck sit for a week + I pulled that spark plug and looked in the cylinder with an inspection camera. Found coolant pooled in the cylinder. Spun the engine over to clear out the coolant, reinstalled the spark plug, and poured in a bottle of Bars head gasket fix (this version). Really hated to use that stuff, but needed the truck running and wasn't interested in doing a head gasket in soon to be 100+ degree weather. Also had to decide if I was going to fix it again or trading it on something else.

Fast forward a couple of months and the misfire has returned. Was driving into town to top top off the tank before hurricane Irma hit when it started, I think the Bar's head gasket fix got scared and decided to evacuate before the storm hit. Can't say I wasn't expecting it, only used it as a temp fix anyway. I haven't pulled the plug and checked again yet, but I'm pretty confident it's the same problem.

Can't find a running/working truck I like in a price range I'm willing to pay for it and will not get back into car payments right now, so fix it is. Also got a punctured tire sidewall last week and tires were due for replacement, so that $600 kinda solidified the fix decision. Now I have to decide if I'm going to pour in another bottle of head gasket fix (one of the better versions), throw more gaskets at it and hope they last, or pay someone else to fix it. Don't have time right now to do proper repair myself, bosses pretty much said we'll be working 10/6 which given driving time means I'll basically be at work 12-13 hours a day Monday through Saturday. If I pay someone to do the work and they do it right it'll likely cost more than I can afford right now, whereas if they just throw gaskets at it (like I expect) I'll be doing it over again in a year or two. Kinda thinking another quick fix in a bottle might be the ticket for now. If it could hold till the beginning of the year I'd have enough saved up for any machine work or a reman engine if necessary.

Thing about Head Gasket Fix is that the seal is temporary, and I mean daily temporary not just temp fix

It is like a liquid glass that hardens at extreme temps, i.e. 1,400+ degsF, like what is found inside a cylinder when it fires.
It seals the breach but as metal expands and contracts it breaks away and then more is needed to reseal it and this goes on daily.
So you need to leave it in the coolant and add more if it gets used up.

It doesn't hurt any thing and will NOT clog up rad or heater cores unless they were already clogged up, because it is made up of small particles they will be stopped in small "ALREADY CLOGGED UP" passages, lol.
It is Common myth about any automotive leak stop product, "it will clog up rad", doesn't work that way