Head Gasket leak?

[Dave WM]

while messing with the spare engine on the test stand I noticed some odd behavior of the cooling system. very soon after starting way before the water temps rise, if I leave the rad cap off it will start puking water up, a lot of water (quart or more), then as the temp rises and I presume the thermostat opens (the water getting puked is cold) everything settles down (after adding water back) and the temps stabilize at 180f per the meat gauge, no more puking water running thru the rad. Next I drained off a little water and tried my napa head leak tester. This is the one that pulls air from inside the rad thru a mesh screen bubbling the blue chemical. It had a tinge of yellow, def lighter color than the dark blue it started out with. I am pretty sure this is conclusive testing but for fun I plan to try using the leak down tester with the rad full up, engine warm, and pressurize the cyl one at a time to see if the water level in the rad moves up (like it did when I was running it and it was cold). the 1st test should be enough but I like to try stuff.

anyway it looks like I may be getting a chance to pull the head off. I don't know if you always have to skim them, but will test it with a straight edge when I get there.

[Reptoid Overlords]

I guess if it is out of spec, then it's a reason to have it shaved.

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[Dave WM]

I wonder if its possible for the head gasket to just fail due to age, and not other underlying factor (that would need to be addressed before just replacing). Any will check. I am going to conduct a test with the chemical leak detector on my running 75 just to see if it will pass the test. Will start with the cap off to see if it wants to burp up water when 1st started as well. I did not have any big compression test fails, everything was between 165-170 warm test so was kinda surprised to see the fail. I had assumed if the HG was bad there would be some compression problems.

[Reptoid Overlords]

Could it be that the head(or gasket) is out of spec cold, and when it gets hot closes the gap?  Many a mark III Supra owner has had a bad head gasket on their 7MGE's due to improper bolt torque, or something like that.  We're lucky the L series don't come with that problem. 

[Dave WM]

More testing this time a leak down test. engine was cold (well never cold in Florida, lets say not hot) rad cap off, tested very well, 90/85 (about 6%) psi on each cylinder and not a hit of a bubble from the rad. Sounded like most of the air was escaping past the rings. (could hear it from the dip stick or down the cam chain area). Running the engine has helped in this regard as it was much worse when I 1st got the engine on the stand (and it had not been run in some time).

I am going to pull the thermostat out and test run it again, try the exhaust gas in coolant test. Wil remove the thermostat  in hopes of not making a mess when it burps. Then will follow up with the leak down and look for bubbles with a fully warmed up engine.

I noticed in the power test pulling the #6 injector seemed to have a much smaller effect during running, but that cylinder test fine in both compression and leak down. I can hear the injector clicking, will prob put the color tune plug in there to see what is going on with respect to the combustion.

[Captain Obvious]

About the burping... I suspect it could just be an air pocket somewhere that hadn't worked it's way out.

If you've got a gas bubble anywhere in the system, it will expand a huge amount compared to an equal volume of liquid and can push vurps of liquid out like that. The recovery tank and two way valve built into the radiator cap is intended to eventually work that gas out of the system and replace it with liquid.

The gas is also compressible though, and it will compress first, before the system reaches the cracking pressure of the cap. If you have too much gas in the system, you may never even reach that cracking pressure because the gas will just compress.

So with that in mind... Do you have a recovery tank installed or are have you been running open system?

[Dave WM]

when its left open (like testing water temps or the leak test for gas) it like to burp. If I just leave the cap on all is fine, no recovery tank, but I have one, maybe will hook up just to see what happens. Temps look good, stays right at 185 per meat thermo which is right in the middle of the gauge, does not move once its there.

no milkshake under oil cap, Oil on dip stick looks ok. I need to flush out the rad and start over again, there is something mixed with the water, but could have been there from when I was hooking everything up. lots of brown yuk came out with the burp.

I am prob over worrying about it since I don't have any other sign of a head leak. only the one test, chem blue, that I want to repeat with some fresh water. Rained last night so I have some nice distilled water.

Edited May 7, 2019 by Dave WM

[Captain Obvious]

My point about the gas being compressible means that it might not be fine. Just because it doesn't overpower the spring in the cap and push anything out, doesn't mean it's OK. In fact... When the system is working properly, there is SUPPOSED to be some liquid pushed out of the cap and into the tank. Then when it cools, that liquid is supposed to be pulled back in.

With the cap on, if you aren't getting anything at all pushed out, that is another indication that you might have air in the system.

[Dave WM]

I presume rad height is important so that air has a chance to work out  as well, I think its ok, but will check that again. Easy enough to hook up the overflow tank so will do that as well.

I assume you want the water level at the rad to be slightly above the highest point (thermostat) of the engine?

[Dave WM]

raised up the rad 2" nothing burped this time, started to overflow as soon as the thermostat came on, but nothing explosive. will still test for combustion gas in rad with chem test later.

another interesting find, I mentioned #6 not having much effect on idle right after startup. I put the color tune plug in, and it was a very lean looking blue, I tried the color tune in #5 and it was def richer, verge of yellow and blue. I think #6 is running lean, I may swap in another injector to see if that changes things. after warming up the loss of power when disabling #6 is less noticeable.

I have it setup for a pretty lean run, the engine will stop if I remove the oil cap. I need to verify the TVS switch is on while idling. I may have bumped in while messing around when I could not get it to start early on in the process.

 

Edited May 7, 2019 by Dave WM

[Captain Obvious]

I've got a tiny (tiny) bit of molding experience, and in my miniscule experience, it can be really really hard to fill a cavity and have all the air be properly displaced by the filling liquid. Since the block and head (not to mention the heater system) are rough and complex internal shapes, I would be very very surprised if you can just pour water into the radiator cap hole and have 100% of the air in the system be exchanged with water on the first try. I bet there would be significant pockets of air remaining after the fill. And that's where the overflow system comes into play.

Putting some rough numbers on it... The volume of air in the system will expand closely related to the ideal gas law, while the volume of water in the system will expand at a much smaller rate. Quick search on the web says the volumetric coefficient of expansion for water is .00021 while air is .0036  .

In other words, for the same temperature change, air expands about seventeen times more in volume than water does. That can certainly cause a vurp.

It is my belief that the air will eventually be trapped in the filler neck as bubbles circulate in the system. The filler neck acting as a vertical trap as the bubbles flow by and getting pushed out the overflow when the system pressure increases. Then (assuming an overflow bottle is connected and has liquid in it) when the system cools down and contracts, it will pull liquid back in where the air used to be.

I also do not believe this happens all at once, but can happen over a number of warm-up / cool-down cycles after filling.

So... The bottom line? I think you should connect up the overflow tank, put some coolant in it, top off the radiator, and then heat cycle the system a couple times. If you are watching the tank, you might even see some bubbles burp out. If that's the case, the level in the overflow tank will end up a little lower than when you started because some of that liquid will be pulled into the system.

And after a couple cycles, hopefully you would have all the air worked out.

[Dave WM]

more test, everything works fine with the engine, no oil noticed in coolant, no milk shake under oil cap, dipstick looks fine, engine runs well on test stand. compression looks good (165ish on all).

however, I do seem to have a lot of oil build up on the plugs after short runs. Perhaps the oil control rings are not doing a good job. And I def failed the combustion gas in rad test (it will turn yellow after about 6-8 pumps. I tried it several times, flushed the rad etc... same result.

So do I just put the engine aside and keep it as a spare (it would be fine I think as such) or do I do a partial rebuild (rings/head gasket)...