Persistent air in cooling system

have browsed on this issue for 2 years now. Have never found a solution. I have an 05 Tacoma with the 4.0 that all was good with until a few years ago when the frame was replaced. While they were in there they did the water pump as well. Since then you can burp the system, purge all air and all is good for a short period of time. The truck will purge out enough coolant to overflow the overflow tank and spill out. Seems to Happen much quicker on freeway and while truck is under load. After 100 miles or less it will end up purging enough out that the overflow will end up being empty. So currently as it sits, the tank is empty and the radiator is low, and there’s air in the system causing lost heat. I’ve replace the t-stat, the rad cap. Had it to two shops multiple times. It’s had a head gasket check and checks ok. There are no leaks, burning smells of coolant to speak of. At my wits end with it. Summer time even with low coolant it will never overheat and is fine. Besides the water gurgling under dash you can here from air.

 

If it’s losing coolant and it’s not an outside leak then it’s a bad head

 

Yep, @Bebop is right. If there are no external leaks and the coolant level keeps going down then it has to be going somewhere..

Headgasket most likely

Its bubbling out of the reservoir because of excessive pressure in the cooling system. The pressure is combustion pressure from the head gasket breach

 

I would make sure all air is out of the system by bleeding it properly, checking / replacing radiator cap. If that’s not it I don’t care what the shops said you may be looking at a head gasket issue. There are ways you can check if you have the tools. Compression check, leak down check or chemical check which you can purchase on Amazon. Good luck.

 

Well, it doesn’t seem to be losing coolant due to burning. It just pushes it out of radiator into the overflow until it’s pouring out of that. The part that has had me so bothered is that it happened right back from Toyota. Coincidence or I always debated something wasn’t quite installed right. I have compression and a leak down tester, however not sure if I have the right thread size for them. Truck never has any running issue and spark plugs are all a nice brown color. I forgot to mention as well that I got the truck warmed up, and did a pressure check through the radiator and it held pressure for the hour I left it last year with a setup I was able to loan from an auto store.

 

Does the temp run hot? Sometimes you cant tell just by looking at the gauge, i like using a little code reader to watch temp while im driving around. If the temp is stable around 190 you could try another rad cap. Maybe the cap is weak and letting coolant escape

 

I do have a scanner tool, never have monitored it while driving. Have tried a few caps. Engine has never ran hot per oem gauge. And after 2 years nothing’s worsened, where as my tundra with the 4.7 as time went on with a bad head gasket it got worse and worse, would overheat etc...

 

On this forum it's not uncommon to read that people with the 4.0L engine will sometimes have code P0305(cylinder 5 misfire) or P0306(cylinder 6 misfire). This sometimes can be indicative of a head gasket issue at either one of those cylinders. You may not have that code at this time, but it might be interesting to pull all of the plugs and see what they look like. If cylinder 5 and/or cylinder 6 look noticeably cleaner than the others, you could be dealing with a head gasket issue.
Pulling and installing spark plugs on the 4.0L is pretty easy.

 

Appreciate the tips, I’ll start checking some of these things this weekend. I’ve debated just doing the headgaskets just to do them to eliminate the mystery of them. Or selling the truck and being done.

 

Sure sounds like a BHG, but the timing is very odd. There should be a tube which runs towards from the cap of the overflow tank towards the bottom of it. It’s purpose is to draw coolant back into the radiator when the truck cools. Make sure that tube is present and there are no cracks/breaks in it or the cap. Don’t be surprised with tiny head gasket breaks if it passes the coolant-exhaust-has test.

 

There is a tube in the overflow. When driving for a distance there will be some fluid that ends up in the overflow from the radiator, once shut off overnight it will suck it back in. I always figured if there was a leak I’d think the system would continually lose antifreeze until gone. It seems like it loses a set amount and then that’s it whether it’s 200 miles or 2k.

 

I'm thinking there's over 90% odds it's a BHG at this point. 05-07's 4.0's were also prone to this.

 

Not the 07s

 

Not sure if I'll get a response to this post seeing as though the original thread was 4 years ago. But I am having the exact same issue as @dkgenerallee Everything hes described in all of the posts is the same thing that's happening with me.
What's weird about it on my end it's been happening now for 8 or 9 months. And 2 and a 1/2 years ago I had my head gaskets and water pump done. Then this past spring I replaced the radiator, the radiator cap, the fan clutch, and the thermostat. To my best knowledge and ability, I have correctly burp the system of air.
Was there a solution ever found as to what was causing your issues?

 

I never did resolve the issue. Multiple shops and head gasket tests resulted in nothing. I ended up trading the truck in in haste because I got tired of getting cold at a stop light idling. Most people may have never noticed it but I sure did. Mine happened after the frame install from Toyota, but at that time an oem water pump was installed too, so maybe something there had a bad seal or defective.

 

As a quick follow up, I then had a 13 Tacoma that the coolant reservoir was always empty. Radiator would always be full no matter how long I let it go, but after 100 miles the tank was drained, and there wasn’t any holes in it… I checked. Apparently I’m just destined to have coolant issues..that issue was never resolved either as it never seemed to cause any grief