Overheated on track - now what?

[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.