Yeah I know what you are thinking, head gasket. me too, but I have tested and tested and looked for signs of a blown head gasket....nota. Can anyone think of a reason for never ending air in the cooling system?

I have bled the system over and over. There is a lot of back story to this, but really just looking for an answer to this particular question.


95 ls400​

 

So where are these 'bubbles?' Head gasket failures not he 1UZ are pretty rare from what I've seen. Is the cooling system pressurizing? Does the pressure seem excessive? What sort of head gasket tests did you do?

 

How can you see bubbles? Its very dark inside the cooling system, did you get shrunk up like in that movie years ago when Rachel Welch and others went inside someones body in a submarine?
https://en.wikipedia.org/wiki/Fantastic_Voyage

Air in system? Yeah a pin hole some place, but then it could spray out too. Something in the coolant that's not suppose to be there? Flush and try straight water and see what happens. Just as a test not to run for ever.

 

The bubbles are from the gasket. Other tests might not show it though...try a test for hydrocarbons from the coolant

 

Head gaskets seem to really pressurize the system, I had a plastic coolant reservoir burst from a bad head gasket and yeah I guess the pressure cap was junk. What do you expect on a 99 grand am?

 

There isn't anywhere bubbles can be coming from except the head gasket unless the coolant is boiling and you're seeing that as bubbles rather than what it is.

 

I can see the bubbles because I have clear hoses installed to help figure out wtf is going on. I will make a video, it is kinda cool to see.
I have used the block tester that has fluid that reacts to hydrocarbons. Done that like 10 times..never changes color. also did compression tests, even used a bore scope to look in each cyl. no coolant in oil or oil in coolant. I have pressurized the system and left it set over night, didn't leak down.

over pressurized? what would that look like? it does pressurize normally.

The boiling makes sense and probably had contributed to the over all problem in the past, even more likely because I live in Denver.


Tons of moving parts with this issue, but you all answered my question. only 2 things can put air in the system, blown head gasket and boiling of the coolant.

 

Cavitation can cause bubbles, and trapped air etc. I've never done the clear hose deal but I'd guess most all systems probably do that to some extent, the water pump is a good culprit too I bet theres some cavitation happening there.

 

Have you letting the car idle with the radiator cap off and let it heat up in case you have trapped air somewhere? I had a issue one time where I had to jack up the passenger side of the car and let it run for a while with the cap off. After about 20 minutes we saw a bunch of bubbles and a little overflow and after that the operating temps went down and no more bubbles. I didn't read in depth, are your temps up?

 

how have you tested? Do a pressure test. System shouldn't lose pressure over a period of several hours.


And bleed it properly, either with a vacuum or gravity bleeder.

Edit: To clarify, I would like to see the psi you pressurized the cooling system and for how long. Has the radiator cap been tested/replaced? How did you bleed the system?

 

I guess no one read this. So I'll quote it.

 

I am curious to see the video

 

There are a few things that can cause pinhole leaks and allow air into the system when hot, namely small cracks and slightly loose/improperly seated radiator hoses. Was the system pressure tested with the car hot or cold?

 

Based on what you said, and assuming your HC and pressure leak-down tests results are valid, I would put my money on an air cavity in the head(s). As that area overheats, it boils the coolant just like a coffee percolator, creating bubbles, that get swept through the system. I suspect you don't see the bubbles until the engine has run for a few minutes, and that air cavity starts to overheat. As recommended, a complete system purge must be done.

 

thanks for all the input. since noone is trolling i will share some back story. This is a motor swap into a toyota rv. I bought an LS 400 and drove it for a month to be sure there would be no problems and it performed perfectly . Once I did the swap it has over heated from day one. At first I figured it was a radiator problem not been big enough so I put the biggest possible radiator I could fit in it. Still had an issue, I did a complete drain and bled and bled and bled to no avail. I did play with different expansion tanks, I verified it was indeed overheating with a thermal gun. I have a replaced thermostat with a OEM Lexis. I have put the water wetter stuff in it finally I put a water pump in it drain the system and tried again, no change. I'm using Toyota read coolant.

It will idle in the driveway or drive on flat land all day long and will not overheat, but as soon as I go up the hill or stomp on a little that's when it starts climbing. I can get it to overheat in the driveway holding the RPM above 2000. If you squeeze the upper radiator hose sometimes you can feel the pressure sometimes it doesn't feel like anything's moving. I installed a in-line radiator fluid filter and the clear hoses going to the expansion tank just so I could see what's going on bubbles and more bubbles and more bubbles I suppose there could be trapped air still because of the boiling point that was made earlier. And since I'm in Denver is a lot easier for that to happen.

So I will continue to bleed for a while since now I'm confident the system is set up correctly and that there are no leaks, unless there's one in the heater core.... That's a thought.

here are the videos, it's interesting and it may be helpful for showing somebody what happens when you're bleeding the system,.