Overheated on track - now what?

[infernosg]

Originally Posted by Pete_89T2

Definitely replace the cap with a new Mazda cap then. If it's not sealing properly, it won't hold its rated pressure, and this in turn will make it more likely to boil over.

If it's not a Mazda T-stat, I'd just replace it. The Mazda T-stat & gasket for it is pretty cheap, like under $15

I'll take a picture of the tear and post, but you're right, might as well replace it as they're only like $10. It looks like regardless of the condition of the engine I'll be needing a new thermostat so might as well pick up one of those as well.

Originally Posted by Pete_89T2

Not that I can find in the FSM. What I do whenever I flush & fill the system is make sure the heater is set to full heat before starting, and after I do the initial filling of the radiator with coolant, I'll let it idle with the rad cap off. When the engine reaches operating temp and the upper hose is hot to the touch, I'll run the engine in neutral at a constant 2~3K RPMs for a couple of minutes, then I'll quickly rev the engine up past 5K & back down to idle a few times, still with the cap off. When the level in the radiator drops (it will as trapped air pockets escape), add more coolant till its full. While you're doing this drill, the coolant level buzzer will sound off from time to time - it's normal. I keep repeating this process until I can't add any more coolant to the radiator. Then I top off the overflow tank with coolant to the full line, put the radiator cap back on, and take it for a drive. Let it cool down fully, check the level in the overflow tank, add coolant if needed to get it back to the full mark.

That all makes sense, but the problem I'm having is with the car on and the radiator cap off I get a lot of coolant coming up and spilling out. Maybe there was just a large air bubble pushing it all out but the pessimist in me says this is the pressure from the combustion chamber. Maybe another picture will suffice...

[Pete_89T2]

Originally Posted by infernosg

That all makes sense, but the problem I'm having is with the car on and the radiator cap off I get a lot of coolant coming up and spilling out. Maybe there was just a large air bubble pushing it all out but the pessimist in me says this is the pressure from the combustion chamber. Maybe another picture will suffice...

I forgot to mention that I remove the radiator cap after the coolant is at operating temp and circulating thru the engine - this helps avoid most of the spilling, since once it's all circulating, the level in the rad should drop a bit. But yeah, if you remove the cap while its still cold and run the engine with the cap off after just filling the radiator, lots of coolant will barf out. Just use a thick rag to keep from burning yourself, crack open the cap to the first stop to release the pressure, let any excess coolant bleed out then remove it all the way.

[infernosg]

Originally Posted by Pete_89T2

I forgot to mention that I remove the radiator cap after the coolant is at operating temp and circulating thru the engine - this helps avoid most of the spilling, since once it's all circulating, the level in the rad should drop a bit. But yeah, if you remove the cap while its still cold and run the engine with the cap off after just filling the radiator, lots of coolant will barf out. Just use a thick rag to keep from burning yourself, crack open the cap to the first stop to release the pressure, let any excess coolant bleed out then remove it all the way.

I did this at the track before heading home and a good amount of coolant came spilling out. Kind of like a slow geyser. I didn't leave the cap off long enough to see if it was going to stop though so maybe that's normal?

So more updates. First a picture of the radiator cap. The tear is hard to see but it's "inside" the "ear" of the cap toward the bottom:





I managed to rent a cooling system pressure tester from the local Autozone as well. First the good news. I checked the radiator cap - it opened at the appropriate 0.9 bar (about 13 psi) but it would not hold any pressure above ~9 psi and even then it still fell slowly. Outright, this makes me believe the radiator cap is dead so there's at least one thing.

Next, the not-so-good news. I attached the pressure tester to the radiator and pressurized the system up to 15 psi. Within 10-20 minutes the pressure had dropped to 14 psi or so. I brought the pressure up to 20 psi next to see if it fell off any faster but it dropped ~1 psi in about the same amount of time. I did not see any external leaks, so something's got to be off internally. Then again, perhaps the seal on the tester wasn't perfect and the engine's fine as I'm not detecting any gas or exhaust fumes in the overflow bottle or radiator

[RETed]

I see the tear - it's trash; replace it.
The system has to be airtight - a tiny leak like that will compromise it's effectiveness.

15psi is about as high as I would go.
20psi is way too much pressure - in fact, most cooling system will start to leak all over the place.
Remember, the stock radiator cap is only rated to 0.9 bar(?), which is like 13psi.

15psi drops to 14psi is okay in my book.
This pretty much eliminate a major water jacket o-ring failure.

Replace the cap...
Burp all the air out of the system...
I think your engine should be okay...
Cross fingers!


-Ted

[infernosg]

Originally Posted by RETed

I see the tear - it's trash; replace it.
The system has to be airtight - a tiny leak like that will compromise it's effectiveness.

New cap already ordered!

Originally Posted by RETed

15psi is about as high as I would go.
20psi is way too much pressure - in fact, most cooling system will start to leak all over the place.
Remember, the stock radiator cap is only rated to 0.9 bar(?), which is like 13psi.

Yeah, I was a little nervous about the 20 psi. My hope was I'd expose any small leaks by really forcing the pressure. I did not start the ar yesterday, but I will tonight and I'll be sure to look for any white smoke from the exhaust indicating I managed to force water into the combustion chamber.

Originally Posted by RETed

15psi drops to 14psi is okay in my book.
This pretty much eliminate a major water jacket o-ring failure.

Yep, it was a VERY slow, seemingly unsteady leak. Not ideal, but like you said, certainly not a major o-ring failure. It probably would have continued to drop some, but I was running out of daylight...

Originally Posted by RETed

Replace the cap...
Burp all the air out of the system...
I think your engine should be okay...
Cross fingers!

This is the plan, along with a new thermostat. I'm considering a new water pump and belts as well because I'm pretty sure they're the original parts.

-Ted[/QUOTE]

[infernosg]

Well, the new radiator cap didn't seem to do anything. Somehow there is still a constant stream of air/gas going into the overflow bottle. Every now and then some water comes with it so pressure is being built up somewhere. Additionally, when I remove the radiator cap with the car running and warmed up it just keeps bubbling like the system never seems to be fully bled. If I add more water while it's running it seems to just want to push that and more out.

I have a new radiator, coolant hoses and water pump on the way (they are probably do to be replaced anyway) but I'm not thinking any of those are failed. Time to start pulling things apart now?

[vex]

Come to the car show...
Borrow tools...
?????????
Profit!

[infernosg]

Originally Posted by vex

Come to the car show...
Borrow tools...
?????????
Profit!

Something tells me a rebuild will take more than a weekend and besides, The Mitty > CCVT car show.

I'm going to try one more bleeding technique as suggested by the Haynes manual, which involves running without the radiator cap with the car cold. If that doesn't do anything then I guess it's time for a rebuild. I can't think of any other reason why I'm getting a constant stream of gases, occasionally accompanied with coolant, flowing into the overflow bottle other than a water jacket o-ring or housing failure.

Bottom line: is there any way this could be attributed to a bad thermostat or leaking radiator/water hoses? If not, like mentioned above, it looks like rebuild time.

[Pete_89T2]

Originally Posted by infernosg

Bottom line: is there any way this could be attributed to a bad thermostat or leaking radiator/water hoses? If not, like mentioned above, it looks like rebuild time.

Not the thermostat, since it's an internal part. But in theory, if water can leak out of an extrenal part exposed to air such as a hose or radiator, then air can get in too. But you tested the system with the pressure tester and it passed, most likely you would have found a leak. Only exception to that I can think of is since the pressure test is done under static conditions (engine not running, at whatever temperature it was at when you tested it), the test could miss a leak that only occurs under some combinations of dynamic conditions (i.e. temperature cycling, vibration, etc.).

[vex]

The only other possibility that I could think of would be that the water pump housing is starting to leak. Whether it's from the impeller or from mating surface would be difficult to say. It wouldn't have to be a large leak. When I did my rebuild that was an issue I had to overcome.

Other possibilities might be cracked coolant lines that run into the heater housing (let alone the heater might be leaking as well). Basically you'll need to track down to see if there's a pin hole leak anywhere in the car.

Or you could just shove a borescope (or a mirror) into the exhaust ports and see if there's any coolant pooling.

[infernosg]

Both valid points. What seems to be missing though is any sign of an external leak. I'm not seeing anything from any of the lines; nothing from the radiator and nothing coming out of the "weep hole" on the water pump housing. By "signs" I mean no leaking fluid, no evidence of dried fluid, no steam while running, no coolant smell, etc. Also, if there were a small leak allowing air into the system wouldn't that air just bleed off and stop at some point? The system is pressurized when the car is running so wouldn't that prevent additional air from entering?

I'm not sure if I'd say the pressure test "passed". I brought the system up to 15 psi and within 10-20 minutes it had dropped to 14 psi. You would think a perfect system would hold pressure indefinitely.

I still think I'm missing something about the bubbling in the overflow bottle. Something is causing a pressure build-up in excess of 0.9 bar but it's not a constant stream of fluid that's coming out like what would happen with an over-filled system. It's a mostly steady stream of gas, whether it be escaping air pockets (but they never stop), boiled fluid (possibly a result of a stuck thermostat) or exhaust gases I'm not sure. I suppose the only way to tell is to have the system checked for the presence of exhaust hydrocarbons but I don't know where I'd go for that.

I have a new thermostat that is not yet installed and a new radiator, water pump and full set of hoses on the way. Is there any hope that installing all those would rectify the issue? If not, I guess I'm just going to have to tear the engine apart.

[RETed]

Sorry to hear it's not going too well...

Have you tried to smell the coolant (bubbling)?
If it's combustion gases getting into the cooling system, the smell will give it away.
Normal coolant smell is a lot diffferent from combustion gases in the coolant.

There is a chance that you have a very tiny break in the water jacket o-ring on the combustion / exhaust cycle of the rotor housing.
The combustion pressures can hit around 1,000psi with the exhaust cycle pressures several times higher than the typical 15psi, and this would explain what you're experiencing.


-Ted

[vex]

Originally Posted by infernosg

Both valid points. What seems to be missing though is any sign of an external leak. I'm not seeing anything from any of the lines; nothing from the radiator and nothing coming out of the "weep hole" on the water pump housing. By "signs" I mean no leaking fluid, no evidence of dried fluid, no steam while running, no coolant smell, etc. Also, if there were a small leak allowing air into the system wouldn't that air just bleed off and stop at some point? The system is pressurized when the car is running so wouldn't that prevent additional air from entering?

No. There is no check valve in a pinhole leak if it's present. If water gets out when at pressure, air will come in when there isn't. It's basic buoyancy and pressure differentials. The system will suck in air wherever possible as it's less dense and requires less energy to reach equilibrium pressure.

I'm not sure if I'd say the pressure test "passed". I brought the system up to 15 psi and within 10-20 minutes it had dropped to 14 psi. You would think a perfect system would hold pressure indefinitely.

I still think I'm missing something about the bubbling in the overflow bottle. Something is causing a pressure build-up in excess of 0.9 bar but it's not a constant stream of fluid that's coming out like what would happen with an over-filled system. It's a mostly steady stream of gas, whether it be escaping air pockets (but they never stop), boiled fluid (possibly a result of a stuck thermostat) or exhaust gases I'm not sure. I suppose the only way to tell is to have the system checked for the presence of exhaust hydrocarbons but I don't know where I'd go for that.

Coolant rarely ever is a constant stream coming out. You'll have some gas, but this is usually just gaseous coolant vapor. If however the system has air when it's coming back in from the reserve tank you have issues.

I have a new thermostat that is not yet installed and a new radiator, water pump and full set of hoses on the way. Is there any hope that installing all those would rectify the issue? If not, I guess I'm just going to have to tear the engine apart.

No. What you might be able to do to confirm where your issue is; would be to break the coolant system into sections. Separate the radiator from the engine section and test each section. For instance you can block off one outlet on the water pump and pressurize the other. Check pressure after a few hours. Do the same for the radiator and you'll know which one's holding pressure and which one is not.

If your radiator isn't holding pressure because the brazing is falling apart that might be your issue, but if you haven't noticed leaks with it.... then well... That's what I'd do at least.

[infernosg]

Originally Posted by vex

No. There is no check valve in a pinhole leak if it's present. If water gets out when at pressure, air will come in when there isn't. It's basic buoyancy and pressure differentials. The system will suck in air wherever possible as it's less dense and requires less energy to reach equilibrium pressure.

You forget you're talking to another engineer here (and a VT AOE graduate to boot), but that is what I was getting at. If air entered through some small tear with the car off (under vacuum) it would be pushed out with the car on. The air would be pushed through the path of least resistance - the open radiator cap. However, because the car is on no additional air can enter so at some point the bubbling would stop. What I have is a constant stream (continues for more than 10 minutes) so this leads me to believe it is not the issue.

Originally Posted by vex

No. What you might be able to do to confirm where your issue is; would be to break the coolant system into sections. Separate the radiator from the engine section and test each section. For instance you can block off one outlet on the water pump and pressurize the other. Check pressure after a few hours. Do the same for the radiator and you'll know which one's holding pressure and which one is not.

If your radiator isn't holding pressure because the brazing is falling apart that might be your issue, but if you haven't noticed leaks with it.... then well... That's what I'd do at least.

I'd love to pressure test every component but I just don't have the means.

I'm inclined to believe ReTed that there is a small failure point likely on the compression side of the rotor housing. This would explain why I don't have a continuous cloud of white smoke because the pressure is keeping the coolant out, but would explain the little bit I get after starting the car after it's sat for a while. It's always done that but I just assumed it was condensation. I can think of nothing else that would cause the continuous build up of pressure. I guess the HPDE just pushed it over the edge. I was really hoping the stock engine would last more than 105k miles...

[vex]

Originally Posted by infernosg

You forget you're talking to another engineer here (and a VT AOE graduate to boot), but that is what I was getting at. If air entered through some small tear with the car off (under vacuum) it would be pushed out with the car on. The air would be pushed through the path of least resistance - the open radiator cap. However, because the car is on no additional air can enter so at some point the bubbling would stop. What I have is a constant stream (continues for more than 10 minutes) so this leads me to believe it is not the issue.

It was more for other individuals reading than for you . Do the bubbles correlate to the heat increase? Or is it independent? IE if you run the engine; reach operating temperature; bubbles stop or bubbles continue but operating temperature is maintained.

I'd love to pressure test every component but I just don't have the means.

And you call yourself an engineer . Hit up Lowes/Home Depot and build your own for less than $50.00.

I'm inclined to believe ReTed that there is a small failure point likely on the compression side of the rotor housing. This would explain why I don't have a continuous cloud of white smoke because the pressure is keeping the coolant out, but would explain the little bit I get after starting the car after it's sat for a while. It's always done that but I just assumed it was condensation. I can think of nothing else that would cause the continuous build up of pressure. I guess the HPDE just pushed it over the edge. I was really hoping the stock engine would last more than 105k miles...

If it's how I imagine it is working than that small failure point is an indication of the casting failing... which 'shouldn't' happen on an S5.