I'm at my Wit's end with coolant problem, need some advice...

I didnt do a leak down with the cap off, everythinge else I did. Check for bubbles while running, pressure test, exhuast gas in the coolant, bore scope the cylinders, check the spark plug color. My truck would only burp coolant when going through the mountains or going 4 wheeling.

I skipped over the part where the OP said his hose was collapsing. Mine never did that but usually if it collapses when cooling its because of a loss of coolant, that spring is mainly there for keeping the hose from collapsing under higher RPM.

edit: what can be happening is that hose is collapsing while youre driving, then engine overheats from lack of coolant flow and burps coolant. Then when you stop and the engine is just at idle the hose pops back into shape. As it cools down with the lower volume of coolant it will collapse that hose back.

 

OP stated he runs about 2700 rpm on the highway.

 

Yeah that would be enough, usually on older cars it was just highway cruising speeds that would do it. Around town it would be fine.

 

Now these 2 just came up. I'm running it without a thermostat at the moment

 

There's no spring in the lower hose on modern engines. That's a throwback to old cast iron American engines

Is the hose collapsing while driving or collapsing after it sits and cools down? If it's collapsing after it sits that means there is a blockage in the expansion tank hose or a faulty radiator cap

 

You sure you got all your intake plumbing and vacuum lines connected properly?

 

And if that radiator drain keeps dripping just pull the petcock out and replace the o-ring. They get square after years of sitting in there

 

I've got the original hoses from 1GR-FE's from a couple of Tacoma's and an FJ, I don't see a spring?

 

I've flushed out the expansion tank several times, is there a way to actually get it out of the shroud and take it aprt to make sure there is no blockage?

 

today, with just normal driving, I have not seen any leakage from the radiator drain plug or that area.

The leak was really evident last night when I had pumped the coolant system pressure up to 17psi

I want to maybe try to recreate the leak again. To me going up to 17psi was a little high. Anyone know how much pressure you can put into the coolant system before you start to risk damage?

 

Look at the radiator cap for the rated pressure, you can go a couple psi above that but I wouldn't go much higher.
Leaks by seals and O-rings typically tend to be cold leaks that seal up as things heat up and expand.

 

We’re getting close but still haven’t done this. If the tank had pressure, as op stated, there has to be a blockage.

 

Take the hose off and blow some air through there. Do you have a air compressor?

 

how can I test the expansion tank to see if there is something blocking the flow of coolant back into the radiator?

a little while ago I noticed the coolant temp was rising. It was at about 192 or so and I turned the truck off. the expansion tank was about 80% full. I carefully unscrewed the radiator cap, expecting that at that temp, coolant would spray out. All that happened is I heard a little air pressure release. I was able to add about a quart maybe a little bit more coolant.

im just getting off of work so I'll be digging into some more in a little while.

 

I see you've done X and X test to check for blown head gaskets, but never did I once see you mention that you did an actual cylinder leakage test on all 6 cylinders (at least I'm pretty sure you didn't). You could chemical test and inspect the inside of the cylinders all day until you are blue in the face, but you'll never get the full story nor an accurate one unless you do an actual cylinder leakage test. Anything over 25% leakage is considered not normal and will likely require cylinder head teardown at that point.

Just because a blown head gasket is not acting in the traditionally known way of them failing by either blowing white smoke out of the exhaust or washing out the cylinders does not exempt it from potentially being blown none of the less.

Now the collapsing of your lower... That's one I haven't seen in a while and usually that issue is remedied by replacing the faulty radiator cap that is causing it. I couldn't tell if you replaced it or not, but just bear in mind that it is not uncommon to pick up a faulty part straight out of the box even if it is from the dealer.

Additionally, a thermostat is never off the table, but testing it is a different story entirely. I see people suggesting all the time to throw it in a pot of boiling water and that's fine and dandy. What people don't think about though is that just because it opens, that is by no means any indicator of whether or not it's opening properly, it only tests as to whether or not the part is capable of opening.

 

192 is not outside of normal temps. Im leaning toward to you got a failing headgasket, see what the oil sample test says.

 

I don't know what ELSE may have happened to it but that collapsed hose means a blocked radiator.

 

Ok, I got leak at the lower end of the radiator fixed. I pressured it up to 17psi no leaking anymore. I filled the system with water for now.

Still running with no thermostat. I put plastic wrap around the fill funnel and zip tied it pretty snug. It's been idling for a good 45 mins.

How can I test is I captured any exhaust gas in the funnel?

 

I keep leaning towards head gasket also but I can't find any confirmed signs.

I'm going to try to find or borrow one of those adapters to hook the shop air compressor to the spark plug holes

 

I held it at 3500 RPMS, after 5-10 secs , I Got a few bubbles. Going to try to replicate