Rotary4tw

iTrader: (3)

Alright. I am struggling to master the basic physics of my coolant system. I know this coolant system is the same as other cars as well, so I really struggle to understand them all.

This is so simple in theory. I suspect an O-ring Failure. What I am trying to do is watch my watertemp rise in a linear fashion with my coolant temperature. If it does this, then I know combustion is not contributing to the pressure in my system. If the temp reaches a certain point, and the system continues to pressurize, forcing coolant out the clear tube I have attached and into an empty milk jug, then I buy a new engine and take this one out to a field and go "office space" on its ***. Simple in theory ehh?

The main question I have been trying to receive an answer to in the last month is the following: "How does air (or combustion gas) travel through the closed, pressurized coolant system if it becomes trapped inside."

It can do one of two things...

1) Flow in the system as an air pocket that keeps re-circling over and over. It would remain in the system even if coolant expanded as it got hotter. The coolant would be unable to "take over" the space of the air. You could get lucky and have it flow out your AST cap once it hit the systems limit, but the bubble would have to be right under the cap at the time of the pressure build up.

or

2) The air/gas will find the highest point in the system, and sit there like a bitch, blocking coolant from passing through that spot if it has other ways it can go. (Apparently the FD's system has multiple ways for the coolant to go, and it's not just one big circle that can get plugged. Take the back coolant hoses for example)

Now, I have heard that it is 1, and I feel that it is 2.

The reason why is the following.

Tonight I tapped my rear coolant line with a T plumbing and attached an autometer mechanical water temp gauge. I turned the coolant on, the engine heated to 190 (t-stat opened, warm coolant lines, stock gauge 50%) degrees, but the autometer temp gauge did not go past 120. I said "Hmm, perhaps it's broken." I then boiled a pot of water, stuck the gauge in, and it shot to 210 in a few seconds. Hmmm, it works.

This tells me... the only way this gauge was not functioning is if the top hose was not getting coolant. The hose was cold on one side, and a little warm on the other... so it must not have been getting coolant. This temp gauge is also the highest point in the system, above the UIM for testing purposes.



Next, I said hmmm, no coolant up top, okay, I want to move the gauge to a lower spot that I know will be getting coolant. So I tapped the gauge into the line leaving the filler neck, and heading towards the AST.

This point is below the highest point in the system, so it should get constant coolant even if the top hose has air bubbles. The system got to about 190 degree's before it even started to register in this line at all, which is just not right. How could this spot not be receiving coolant? I felt the lower radiator hose when my temp gauge was still reading nothing and the thermostat opened well before this gauge saw any action at all.

So it finally began to register and shot up to about 210 degrees before it started to leak a little bit from my non-tightened down T-plumbing. This forced me to end my test for the evening.



I can think of 2 ways to determine if my o-ring is bad in my engine, please advise me if you agree with these tests, and if you think they will be conclusive.

1) As I already stated... I watch my watertemp rise in a linear fashion with my coolant temperature. If it does this, then I know combustion is not contributing to the pressure in my system. If the temp reaches a certain point, and the system continues to pressurize, forcing coolant out the clear tube I have attached and into an empty milk jug, then I buy a new engine

2) I let my system warm up, run it for 20 mins... let it pump out all the fricking coolant it wants into a milk jug once it exceeds the systems cap limit. Then, I let it sit for x amount of time until it cools. If all of the pressure was created in the system naturally (from expanding coolant) then when it cools, it will suck each and every drop back from the jug and into the system. If I come back after the system has cooled, and I see there is still coolant in the jug, I will know that the pressure was either created by the combustion, and therefore forced out more coolant then the system would naturally draw back, or... the pressure has escaped through the o-ring seal and there is nothing left in the system to retract the coolant. Either way it's time for a new engine.

In my frustration I made a bunch of low quality images to help me understand the system...

I was planning on using them to help explain what was happening, but I don't really have a need for them anymore.

They are just here now for comedic effect, so enjoy!


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Thank you in advance to any comments regarding how air gas flows through a closed system, or how my two options will determine if my o-ring is bad.

Rotary4tw...

chinoflyer

iTrader: (1)

calm down my man don't get all work up! if i understand your question right. you are suspecting that your engine is blown because of your new gauge is giving you some funny reading. Right?
well i just finish installing my temp gauge too. I did it at the TP line, and i was getting the same thing you are. but then i realized there are may be air trap in the t-fitting, since my fitting are setting just like yours with the tip pointing up. so i turned the fitting around and point it down, and it then it works. so try turning the T fitting around and see what your gauge reads. hope this help.

Banis

why don't you just get the cooling system presure tested?

Rotary4tw

iTrader: (3)

I did... very slow leak.

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I replaced the AST cap on my system, and it is rated for 16psi. I tested/replaced all connections from the AST to the overflow tank with clear tubing, and the system expanded, and appeared to retract coolant back into the system when it cooled down.

I finally got a pressure tester kit with the proper adaptor from Damian. Damian is the man, but most of you already know that. (FYI, the ones you get with the "Loan-A-Tool" program at AutoZone will not fit many import cars, and the adaptor is a $50.00 pep boy part)

Not knowing what to expect, I hooked the system up, and pumped 15psi into the system. (The cap is a 16psi cap)

At about 13psi, I could hear bubbling in the overflow tank, which means there was some pressure escaping the brand new ast cap. So either the tester is off a little or the cap is over-rated a few psi, I can deal with that.

When pressurized, the system slowly loses pressure at a rate of about 1psi per 6-8 mins. At first I thought it might hold steady and not slip, but it kept dropping. There are no coolant leaks anywhere, and the pressure kept dropping well below the 13psi mark. (Where I think the caps limit may have been)

This is all with a cold system granted. Next, while cold, I depressurized, and then hooked the tester up again to run the engine, and monitor how pressure would build up.

There are my results.

1 min -- 1psi
2 mins -- 1-2psi
4 mins -- 4psi
7 mins -- 7psi (Thermo opened at this point)
10 mins -- 13psi
12 mins -- 17 psi
14 mins -- 18 psi *System shut off at this point*

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scotty305

iTrader: (2)

When you started your car after your coolant pressure test, did white smoke come out of the tailpipe?

If so, that's a pretty good indication that coolant seals are letting coolant leak into the combustion chamber, and vice-versa.



From what you wrote in your first thread here (overheating multiple times on the long drive home), I think it's safe to say that your coolant seals are now shot, even if they might have been good when you first bought the car (which is somewhat doubtful, due to the lack of undertray).


Sorry to be the bringer of bad news,
-s-

tsmysak1

Great post...I get into these kind of projects myself, so I really appreciated it.

So did you ever get any exhaust indication that there was coolant in the combustion chamber? I would suspect it immediately after the leak down test, because you know you are forcing coolant somewhere if you loosing pressue...Otherwise, there is something else going on...

Rotary4tw

iTrader: (3)

When I start the car, sometimes I have a small .5 second puff of smoke... but it's not something you can see from the drivers seat.

You have to get out of the car and stare at the tip and then it's almost gone before you even see it. Very small ammount.

I'm going to test the car today... run it... let it pump out coolant if it wishes, then let it cool and see if it draws it all back in.

If it can't draw the coolant back in from expansion, I will know the expansion was not heat based, but rather combustion gas based.



I still want to know:

How does gas/air travel through the coolant system... 1 or 2?

DaveW

Quote:

"It can do one of two things...

1) Flow in the system as an air pocket that keeps re-circling over and over. It would remain in the system even if coolant expanded as it got hotter. The coolant would be unable to "take over" the space of the air. You could get lucky and have it flow out your AST cap once it hit the systems limit, but the bubble would have to be right under the cap at the time of the pressure build up.

or

2) The air/gas will find the highest point in the system, and sit there like a bitch, blocking coolant from passing through that spot if it has other ways it can go. (Apparently the FD's system has multiple ways for the coolant to go, and it's not just one big circle that can get plugged. Take the back coolant hoses for example)"

Unquote

The air in the system should flow to the top of the filler neck (one of the highest points in the system) and then flow to the AST through the hose near the top of the filler neck. The AST traps the air (up to its capacity). As the coolant expands, the trapped air is forced out of the AST into the overflow tank. When the coolant contracts, coolant is drawn back to the engine in place of the expelled air. Therefore scenario (1) is correct, except that the air is expelled as I described.

If the quantity of air in the system is too large, or increases too quickly (coolant seal problem), the AST can't cope, and excess air will remain trapped in the system, and (2) will occur.

93Efini

i wouldn't say your seals are "shot" but they are damaged...if they were really bad you'd have alot more than just half a second of white smoke...mine had about 5 mins + of white smoke after alot of coolant got in the combustion chamber..and now im having to rebuild it of course...if you had a really bad coolant seal, their is no way you would of made it back with that car from your trip...you should try some purple power degreaser and CRC Block Weld as mentioned before <<< this would probably work in your case, since your coolant leak isnt too bad

RCCAZ 1

iTrader: (10)

Were your fans running at the 14 minute/18 psi mark? If not, try turning on your AC so the fan motors kick on and see if your pressure drops or continues to build. If it continues to build, it's bad news I'm afraid.


I may be wrong, but I think for the cold test you should attach the tester to your AST position, not the fill neck, and pump it up to 18 to 20 psi. See if it holds pressure in that position. Mine loses about a half psi in the first 20 minutes, but then holds the remaining pressure indefinitely. I'm pretty sure that a healthy motor should see NO pressure loss. Still, every time I drive her now and open up my fill cap the day after I'm needing to add a small amount to keep the system full and my overflow tank to the "F" position on the dipstick, so who knows. Again, like you I have NO smoke on startup and car fires up right away. One thing I do see with the car running and an expansion funnel attached to my fill neck is a minute stream of champagne bubbles, which indicates to me that a rebuild is coming soon. Too bad since my car is running the best it ever has. Wouldn't you know!

nopistons94

when you start your car the OMP injects oil into the combustion chamber for apex seal lube upon initial start up. Every RX7 will smoke a little bit no matter what on startup unless your OMP is not working properly. If is just that little puff and its not sweet smelling then thats all it is

Rotary4tw

iTrader: (3)

DaveW,

I really appreciate the comments. Hmmm, that seems to make perfect sense! So basically if you burp your coolant system properly and don't have any o-ring leaks, the AST is not needed. That would be nice to someday be in a position where I could remove mine!

93Efini...

I'm also thinking the same... I'm going to likely try a liquid weld like CRC block or something, at least while I wait for a new engine to arrive.

I have heard that when you have a seal that's bad it blows white smoke for at least 15 seconds after a night of sitting. Also, I have no coolant in my oil, nothing on my plugs, and little to no air bubbles.

RCCAZ_1

I just retested the system, and actually this now confuses me even more.

Here is what happened.

Instead of measuring the mins and the psi, I measured the temp and the psi to see if they would go up in a linear fashion. For the most part, they did, and the system didn't kick out any coolant. When it got near 16psi, just then the fans would kick on, and it dropped the pressure from 16psi down to 11psi... then the fans would turn off... pressure back to 16psi, then the fans came on... it cycled this 7 times over the course of 15 mins of idle. I couldn't get one drop to overflow past my AST cap.

Temp PSI

180 6psi
185 8psi
190 9psi
195 11psi
200 13psi
205 14psi (fans kicked on here)
210 11psi

from this point the system would bounce back and forth from 11-16psi, each time reaching 15/16psi, the fans would come on and drop the pressure to 11. The temp never moved too much, down five when the fans came on, and then back up a little bit.

After about 20 mins the system seemed to just keep cycling... so I turned the engine off...

The psi dropped to 13-14 and just kept bouncing back and forth between there every 5 seconds or so... the temp stayed right around 200 for about 5 mins...

Then the temp started to drop... and the pressure started to drop as well...

180 11psi
160 8psi

After 45 mins... the autometer reads below 120, and the system still have about 3psi left in it.

Nothing has exited the line and into my overflow bucket. (It's a clear line and a clear bucket, so I'm 100% it didn't lose anything from the system)

I'm on my way now to go purchase one of these to remove all air from my system and do some more testing tonight.



This whole experience leads me to believe that perhaps my leak isn't as big as I once thought, and that it could possibly be temp fixed with a liquid weld.

I'll keep you all posted.

-Rotary4tw

David Beale

Sounds like you don't have a problem. BTW, it's #2. Any excess air in the system tends to collect below the filler cap. If you could mount the AST as the highest point in the system, the air would collect there. Currently, the AST is a secondary system - it doesn't see all the flow nor all the air bubbles. This was done to slow the flow through it down, so the "tiny bubbles" could settle out. So it take a while for it to collect even all the "tiny bubbles" it was meant to deal with.

The AST removes tiny bubbles created at the bottom of the engine by the very high heat of this turbo-charged engine. I replaced mine with an aluminum one, which I recommend. Others have good luck without it. You do need a filler tube with an overflow pipe if you try to go without. Some RX-7s can't be modified this way, as the casting is not separatable.

Here is my "disertation" of how the system works.
Think of the engine as a coolant pump to and from the overflow bottle.
When the engine warms up the coolant expands and forces its' way through the overflow tube into the overflow bottle. When the engine cools down it creates a vacuum, which sucks coolant back from the overflow bottle.

This works fine until one of your coolant caps develops a vacuum leak at the rubber seal. Then all that happens is some percentage of the coolant in the engine is pumped into the overflow bottle and remains there, leaving the engine a little low. This allows the pressure to drop after shutdown (because air is compressible), which in turn allows the coolant to boil after shutdown. The metal in the engine holds a lot of heat when the engine is running, and this is ok as long as there is coolant flow to carry it away. Once the flow stops, the coolant will heat up more than normal, and if the pressure is low enough, it will boil.

The classic event run is you notice the engine coolant level is way down (checking when cold, of course) when you look in the water pump fill tube. You pour in more water. It gets pumped into the overflow bottle (to stay as you have a vacuum leak and can't get it back to the engine). You are now nervous, and check the level in the engine every day (morning when the car is cold), and fill it. Soon (two to three days) the overflow bottle is full to the top and leaks out where the filler tube (removeable) joins the bottle. You see the puddle and panic.

It happened to me. Solution - replace both caps (they were old), replace all small coolant hoses to/from overflow bottle (they are not designed for pressure use as there is no pressure in this part of the system, so they are thin and can be collapsed under suction - topping the coolant from returning to the engine. I replaced them with suitable pressure coolant hose routed so it would not kink (it's
thicker so care must be taken when routing it - it will not bend as well).

You may just need to "burp" your system.

CantGoStraight

These O-ring failures can happen in differt areas of the O-ring it self. This can lead to different symptoms and show up differently depending on where they fail. It's generally near the exhaust port on the motor (due to heat and pressure and thin metal) and in many cases is the same as a blown head gasket to a piston motor. You have to remember if it can't hold pressure then it boils sooner (lower temp) when it cools it will pull air back into the system instead of coolant and create an air pocket to run around the system. It's a mute point which way it happens, once it has happened as there is only one way to really fix it.

Rotary4tw

iTrader: (3)

Does this compression test give any indication of where the failure may be... or would we need to know the starting location of the rotor before the test was given? (This is from 2 days ago... some of the experts said the only way for you to get this pattern is from a failed o-ring)

scotty305

iTrader: (2)

Temp PSI

180 6psi
185 8psi
190 9psi
195 11psi
200 13psi
205 14psi (fans kicked on here)
210 11psi


^^This is a good indication, in my opinion. From physics class, PV = nRT; pressure will rise and fall with temperature, if the volume is held (relatively) constant. If you had a badly blown coolant seal, you would most likely see a dramatic increase in pressure when the thermostat opened at 180 degrees.


-s-

WaLieN

What ever happened with this "project" of your's?

technonovice

Ditto