Slow bubble in coolant overflow

So I recently got a used 99 Taco (the red one in this post: https://www.tacomaworld.com/threads/new-to-taco-world.488218/#post-14997254 )

It's been running nice, idle is a little rough but aside from that pretty good. This last weekend, I went through and did all the fluids including coolant, new wires, new plugs, fixed a few vacuum leaks on the intake hose, cleaned the MAF sensor, etc. All the usual 3.4 V6 tune ups. Anyways, before I did all this I noticed that I heard a little "leaking" sound from the radiator cap after I shut the truck off. I figured it was a bad cap so as part of the coolant flush I put a new OEM cap on. Coming home from work today, I realize that I have the exact same symptom. I looked in the coolant overflow, and I was getting a bubble coming out of the hose about every 4 seconds (this is with engine off). After a few minutes this all seemed to stop. I will try starting the truck up without the cap on tomorrow and see if I get bubbles after the t-stat opens. Note that truck seems to run at proper temp, no overheating, no visible leaks anywhere.

Giving the symptoms I have described, do I have a small head or head gasket leak? Or am I being too picky? Truck has ~290K miles on it at this point, and if the guys recipets are to be believed the gaskets were replaced around 240K. I'm worried that they didn't check the heads for leaks and we have a crack in them...

Thanks for any tips!

 

It may still be working some air out.

 

You could also look into another cap, I bought a new cap, and it was trash, so I got another one, and my problem was solved

 

Was it OEM? Part store ones are trash.

 

I wouldn't be too concerned, its very common for a big air trap to be at the heater core after draining the radiator. its not a bad idea to add a radiator flush "tee" by the firewall to purge the air out but then how often should you really be draining the coolant system lol.

I suggest you disconnect the hose at the firewall and let the air out then fill the hose up and reconnect it, then turn the heat temp on all the way (fan speed can be on low, it doesn't matter) then rev the engine up or go for a drive at freeway speeds to let the flow push out any remaining air trapped in the heater core.

 

It was a cheap autozone one, and after that I went to my local parts store( they owner is my neighbor) and they got me a nice one made in The USA that's been working great.

 

Yeah them USA ones are not good. Its why we drive Toyota's. JDM (OEM) only.

 

Thanks for the replies so far. The new cap (and it looks like the old as well) are Toyota OEM caps (which appear to be Slater brand?!). I guess my concern is from the fact that every time I turn this truck off I hear the cap "venting". I have not noticed this on my other 2 1st gen's but that doesn't mean they don't do it! It sort of makes sense that the cooling system would be venting right after you turned things off because you are still getting heat from the block but you just lost all your radiator air flow. Unfortunately I currently have a bad head gasket on my other truck so I'm suddenly nervous that the truck I bought to replace it has the same issue.

 

I got that backwards, the Japanese one they ordered worked, not the USA one haha