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SEARCHED: positive coolant pressure when car is dead cold-what's wrong?
I've searched for the past couple days and found nothing so I'm starting a new thread.
I have positive pressure in the coolant system when the car is dead cold. The car has been slowly losing coolant since I took it out of storage a couple months ago. I first noticed the positive pressure a couple days ago when I opened the filler cap (on the water pump housing) and coolant blasted out with such pressure that it blew the cap a good 10 feet away. I topped the coolant off, sealed it up, took a shower, went for a short drive and parked it. I opened it again this morning, after letting it sit 3 days since the last drive, and the same thing happened. The water temp the first time was 23c. I didn't check the temp the second time but the car was stone cold. I have checked for air bubbling up, indicating an O-ring problem, and haven't seen any. I did notice that after idling the car for 2 minutes without the filler cap the coolant level rose approximately 1 inch and started overflowing. I know the coolant expands as it heats up but it was well below operating temp. The ast was replaced with another stock unit last summer. All visible coolant hoses (rad and ast) appear to be fine, but I'm not sure about the condition of the lower hose. The AST is mounted upright but slightly below the top of the radiator, which is also mounted upright to make room for my FMIC. Somehow additional air or liquid is getting into the system and is not able to get back out. What's going on here? Is the ast too low? Is air getting sucked into the system when the water pump cavitates? |
it needs a motor soon
mike |
Is it true that coolant taste's sweet?
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Originally posted by j9fd3s it needs a motor soon mike |
Is it true that coolant taste's sweet?
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Since the AST pressure cap is suppose to vent pressure over its' designed value and also allow backwards vacuum flow, then it must be either defective, or a hoses is pluged. This also applies if you got rid of the AST with the FC type system.
Have you modified the stock cooling system? |
I have a PWR radiator mounted upright. The AST is mounted behind the radiator at about the same height, but not above it. I'm not really sure this matters but I thought I'd mention it.
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check your rad caps, or running pressure.
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AST suppose to be higher than any other parts slightly.
I think the correct working order of it is to have it filled with half full coolant. If its lower than radiator, it may cause problem since it will be full of coolant, thus not releasing any air out... Its a kind of pressure relief when the air pressure gets too high... |
hmm.....I'll see what I can do.
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enough pressure in the system to blow off the rad cap 10FT that is not a good thing. any white smoke out the exhaust ?
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I think that cewrx7r1 is on the right track with fautly caps and/or hoses. If it is staying THAT pressurized for 3 days without filling up the combustion chamber with coolant, i wouldn't suspect a blown o-ring.
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Originally posted by ZoomZoom Is it true that coolant taste's sweet? :bigthumb: good luck! |
Tastes sweet for animals. :D
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I'm stumped on this one though. Why would cold coolant have pressure?
I'll help you fix it (go for a joy ride in it). :D |
when i first got my car. i said it can't be coolant seals. its gotta be these stupid rad caps.......... yeah it wasn't the rad caps ;)
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Thanks for the vote of confidence Vosko;) In law there is a saying "plan for the worst hope for the best. Also applies to RX7 ownership.
Couple things to consider though: -If it were the o-rings wouldn't the coolant flow INTO the motor rather than air flowing out when everything is cold? I've never heard of it going the other way around. I can't think of a senerio that would cause this to happen. -no bubbles in the filler kneck when the T stat is closed. -no white smoke on startup. |
Originally posted by CCarlisi Thanks for the vote of confidence Vosko;) In law there is a saying "plan for the worst hope for the best. Also applies to RX7 ownership. Couple things to consider though: -If it were the o-rings wouldn't the coolant flow INTO the motor rather than air flowing out when everything is cold? I've never heard of it going the other way around. I can't think of a senerio that would cause this to happen. -no bubbles in the filler kneck when the T stat is closed. -no white smoke on startup. 2-3. it might not be that bad yet mike |
Originally posted by vosko when i first got my car. i said it can't be coolant seals. its gotta be these stupid rad caps.......... yeah it wasn't the rad caps ;) |
Update: Today I tried to raise the ast by first removing the rubber tab connecting the bottom of it to the frame cross member. As I pulled coolant started squirting out of the line that goes from the bottom of the AST to the radiator. Apparently a sharp seam on the cross member punctured the line. This may have been caused by vibration ect OR I may have done it as I was trying to remove the tank. I'm hoping for the former since the later would rule it out as a possible cause of my problem. That would certainly account for a loss of coolant, but still doesn't explain the high pressure. I'm going to work it through in my mind and hopefully I can come up with something.
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just keep an eye on it and if starts overheating shut it down. i drove my car with blown coolant seals for almost 6 months. i carried atleast 3 gallons of water and a few quarts of oil at all times. oh yeah my oil seals went too. man those were the good ol days :D
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it seems like there are lots of coolant problems..what do you guys to do "fix" or prevent the problems? mod the system
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Replace all coolant hoses. Replace radiator. Replace/remove AST. Replace thermostat. Get better temp reading equipment than stock. Perform some variation of fan mod.
And THEN replace the engine! :) |
I spoke to Dave at KDR. He suspects a coolant seal on the combustion side of the block. He said one way to check is by looking at the spark plugs with a magnifying glass to see if there are "little white hairs." That is apparently what coolant looks like on the plugs. Does anybody have more information on this test? -when should I do it? should I let the car sit, start it then check? That seems like the most logical time since the coolant would have a chance to leak into the chamber(s) but wouldn't be completely burned off.
I redid the Champaign bubble test yesterday using the sprite bottle. There were no bubbles present from cold to 82c. To be thorough I decided to watch it cool since my system seems to be pressurized even when the car is cold. I noticed a couple large bubbles during the first 10 minutes. Not sure if that's relevant. Has anybody done this test with a healthy motor? What other tests can I preform? -standing pressure test: that seems kinda pointless since my system is able to hold + pressure for days at a time. -smog sniffer test: is there is a point to doing this if I don't have any bubbles? -tail pipe test????: is there a precise way to check for coolant in the exhaust besides checking for an odor? I don't trust my nose enough to use it as the basis for writing a $3000 check :p I know a lot of this stuff has been covered in other threads, but there is not much detailed info. I'm looking for specific instructions. |
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What is the coolant to water ratio you are using?
If the sprite bottle test is what I think it is, get someone to modulate the throttle and keep the engine at 2500-2800 rpm after the car warms up, then look for bubbles. Some coolant leaks are very minor and only happens through driving conditions. It sounds like you have a minor leak that only occurs with higher engine output (not idle). |
I use around 70/30 water/antifreeze. I'm not completely sure of the ratio because I've been adding on a regular basis.
After the car warmed up I reved it to 3000+ a couple times. The coolant would suck down the funnel for a sec and then return to normal height. I didn't notice any bubbles. The only time I saw airbubbles was after the car was shut off and it was cooling down. Every now and then a large air bubble/pocket would rise to the top of the funnel. it didn't foam and there weren't many of them. I'll try the test again and hold the throttle at 3000 rather than blipping it a couple times and see if I get a different result.https://www.rx7club.com/forum/attach...postid=1808745 |
Originally posted by Trexthe3rd What is the coolant to water ratio you are using? If the sprite bottle test is what I think it is, get someone to modulate the throttle and keep the engine at 2500-2800 rpm after the car warms up, then look for bubbles. Some coolant leaks are very minor and only happens through driving conditions. It sounds like you have a minor leak that only occurs with higher engine output (not idle). |
How long ago did you put in the PWR rad? I put a PWR rad in my old FD back in december and it took me until January to finish bleeding it. The whole time, the system would hold pressure for days. Then after all that time I finally got the last of the air out of it. The system returned to normal cycling and everything was fine.
I'd like to say now that the car has run fine ever since but the car was t-boned by a prick in a SUV 3 weeks later. Although the motor had stopped taking water and holding pressure, I have to be honest and say that there was some traces of white powder in the filler neck. Since the car was not using any water during this time, nor was it misbehaving in an other way, I have a theory that powder was from the radiator I forgot to flush before installing. In short I think you're ok. Just keep bleeding it. -pete |
I installed the PWR in early August. I went through the same bleeding process then it stopped. My current problem started up a month or two ago. losing coolant is one thing, but what I'm more concerned about is the fact that something is pressurizing the coolant system.
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Almost forgot- Mike (aka zoomzoom) you're an A$$hole :D
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Originally posted by CCarlisi Almost forgot- Mike (aka zoomzoom) you're an A$$hole :D Check the Filler neck nipple going to the AST, and Check the Hoses going to the overflow. The only way this can happen is if you are not venting the pressure, or if your coolant is reacting to something. Change to a 13lb cap also. |
Chris and I have talked about it. I figured he needed some comic relief
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Here's the latest analysis of my problem. If anybody agrees, disagrees or just thinks I'm putting too much thought into this and should write a check and be done with it let me know.
1. There may be an o-ring leak on the compression side of the motor. 2. The leak is big enough for air molecules (O2) to fit but too small for water (H2O). 3. When the motor is running there is a positive pressure gradient between the motor(+) and the coolant tubes(-) passing through the block. 4. This pushes combustion gas into the coolant system, although no bubbles were visible up to 82C using the sprite test. The presense of combustion gas in the cooling system pushes coolant out through the overflow tank. http://members.aol.com/_ht_a/ccarlisi/page/RX-7/cool1 5. When the car is turned off the gradient reverses; the cooling system goes to (+ pressure) relative to the motor. 6. Coolant cannot enter the combustion chamber however because the o-ring leak is not big enough. 7. The leak is big enough for air, but due to the density gradient between air and water the air is located at the top of the cooling system. In order for the air to pass back into the motor through the leak the air would have to move against the air/water gradient-ie down. 8. Because the air will not do this the cooling system retains pressure even after the car has been shut off. http://members.aol.com/_ht_a/ccarlisi/page/RX-7/cool2 WHAT TO DO? I think I can test for the leak by draining all the fluid out of the coolant system and filling it with compressed air. If only air is in the system there will be no density gradient to prevent the air from leaking into the combustion chamber. Where can I find info on how to do this. If anybody has a good place to find info on doing a standard coolant system pressure test please let me know. |
I think you should fill it up with this pink stuff! If the car starts playing Boy George on startup, you know the O-rings are bad!
You're welcome, in advance :) |
Originally posted by JBurer I think you should fill it up with this pink stuff! If the car starts playing Boy George on startup, you know the O-rings are bad! You're welcome, in advance :) |
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L.O.L. Alright fruit loop stop hijacking my wonderful thread.
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Actually, there is a flow in the theory. Regardless of what happens when hot, after cool down, both liquid and gas will contract (even more so with gas). So there shouldn't be any positive pressure in the system.
My o-ring went bad on the last motor, the coolant was being pushed out of the overflow, but after cool down the coolant system would still contract and create a negative pressure. |
Lets take that apart. The coolant system, if completely sealed, can hold positive pressure up to the limit of the radiator pressure cap. Everything above that value will be bled off into the overflow tank. Now assuming nothing entered the cooling system, you're right once the system cooled the pressure would return to zero or negative if fluid was pumped out when the coolant was hot.
However, in my case air is entering the cooling system and pushing out the water. Suppose the coolant heats up and produces .5BAR of pressure in the system. Next, combustion gas/air enters the cooling system upping the pressure to .9+ at which point fluid is pushed out of the system. Next, the car is turned off so the fluid cools and the pressure is reduced. As you said the air would also cool and exert less pressure. However, this does not mean cooling system pressure will be zero. The amount of air that could be transferred from the combustion chamber into the cooling system is determined by the gradient between the two, and not with reference to the starting volume of the coolant system. The motor will pump air through the leak until the pressure inside the cooling system equals that of the motor. Since the cooling system is limited to the release value of the pressure cap we know the max cooling pressure at shut down is .9 BAR. Even after the air cools there may be enough of it in the system to exert sufficient pressure to raise the total system pressure above the original starting value. This is where my goofy diagram comes in. I'm trying to figure out why the air or coolant isn't bleeding out the hole it came in through. If the hole is too small for water to get through and is near the bottom of the system, preventing air from escaping, zero pressure could not be restored. |
It's got to be one of two areas, the overflow line with pressure cap, or the ast line. They are the gates to decompression, and if either are shut, then you will trap pressure.
https://www.rx7club.com/forum/attach...postid=1822999 https://www.rx7club.com/forum/attach...postid=1823005 |
it's not trapped air in system
Originally posted by CCarlisi ..... The motor will pump air through the leak until the pressure inside the cooling system equals that of the motor. Since the cooling system is limited to the release value of the pressure cap we know the max cooling pressure at shut down is .9 BAR. Even after the air cools there may be enough of it in the system to exert sufficient pressure to raise the total system pressure above the original starting value..... Normal operation, I get 1/3Qt coolant expansion into tank, about 210F t0 70F swing. Assume you have 1/3Qt of hot air at .9 bar trapped in system at shut down. That's about the volume of the stock ast, and normally would trip low coolant light. When engine cools aft sd, the coolant in the engine and rad will contract that same 1/3 Qt. The trapped air volume doubles to 1Qt, if no coolant returns from overflow. Just based on this air volume expansion, the air pressure is cut in half (PV=nRT), so absolute pressure goes from 13+14.7 to 13.85 psi absolute, or minus .85 psi on a gage ...vacuum condition. This ignoring contraction of air due to cooling. Now assume u have 2/3Qt of hot gas trapped at .9bar, then shut down and cool. When cooled, the new volume of air is 1Qt. Due to volume change, the new air pressure is 2/3(13+14.7)=18.46 psia, or 3.9 psi on gage (sea level). Now consider the temp change of air, 210F to 70F. Using absolute pressure and temp units, the change in pressure is 3.8 psi due to temp only, so this puts system pressure at zero psi on gage. Bottom line, no way u could run with enough hot air in the system to cause very high residual system pressure when cold. Even with 1/2 gallon of hot air, the cold residual pressure would only be 5 psi. |
Originally posted by spooledUP7 It's got to be one of two areas, the overflow line with pressure cap, or the ast line. They are the gates to decompression, and if either are shut, then you will trap pressure. https://www.rx7club.com/forum/attach...postid=1822999 https://www.rx7club.com/forum/attach...postid=1823005 Anyway, my car had a similar problem but it had to do with the radiator cap and the inside valve of the cap being stuck suck due to cruds in the system. New cap solved it. |
I haven't seen you mention it yet, but have you even replaced your pressure cap yet? If you are not seeing bubbles using the sprite bottle trick, I don't see how if could be a blown o-ring.
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Originally posted by pomanferrari That is some bad ass animatronic graphics. How do you do it? Originally posted by pomanferrari New cap solved it. [/B] Originally posted by paw140I haven't seen you mention it yet, but have you even replaced your pressure cap yet? If you are not seeing bubbles using the sprite bottle trick, I don't see how if could be a blown o-ring.[/B] |
Kevin, Spooled up, Poorman, paw140, great replies guys. Thanks to everyone for taking time to think about this.
1. I have not replaced the pressure cap but am going to do so for the hell of it 2. I have visually checked all lines going to the ast from the top of the car. I¡¦m going to remove the belly pan and check from underneath next week. 3. I¡¦m going to remove the ast and use a 2nd gen setup for the hell of it. 4. Poorman can you describe your symptoms? Did you have high coolant pressure WHEN THE CAR WAS COLD? 5. I removed my plugs and photographed them under a microscope to look for ¡§white hairs/coolant.¡¨ I also did this with a healthy fd to get a bench mark. There is a lot of white stuff on both plugs, which I¡¦m assuming is just combustion soot rather than coolant. I didn¡¦t see any hairs. If anybody notices anything in these pics let me know. MINE: http://www.hometown.aol.com/ccarlisi/page/RX-7/CCplug1 http://www.hometown.aol.com/ccarlisi...X-7/CCplug1x10 HEALTHY FD: http://www.hometown.aol.com/ccarlisi/page/RX-7/bmplug1 6. I have talked to Atkins, Pineapple and KDR about my problem. They have all suggested I do a pressure test and a smog sniffer test. I asked Dave why I should bother doing the pressure test given that my system holds pressure. I thought his response was interesting so I¡¦m posting it below: ¡§Hey Chris.....the emission sniffer is a good way to tell ...also you can put a pressure tester on the system..dont pump it up...but start car and let it run and build pressure..if you start it up and it immediately builds max pressure you know the seals are gone....but if it takes the normal heat cycle to build 13-15 lbs then they are probably ok...hope this helps..dave@KDR KDR Performance Inc.¡¨ 7. I rented a pressure tester yesterday from autozone but it¡¦s too big for my filler neckƒ¼ I¡¦m going to drive back to autozone and see if they have another. |
If you have an aftermarket AST with the normal sized cap, the pressure tester should fit there.
About Dave's comment regarding building up system pressure right away: if this were the case you would see bubbles coming out of your filler neck. You did the sprite bottle thing and didn't see any bubbles. If I were you I would replace the pressure cap and see if that fixes it. You're spending too much time thinking about it and theorizing, and pressure testing, and everything else when your symptoms all point to a faulty pressure cap. You should be able to buy a cap from Autozone. If that doesn't work, then start with your other stuff like removing the AST (which won't fix your problem). Good luck, Paul |
So, have you fixed it yet?
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no:( Here's the latest:
1. pressure tested the system as Dave suggested. The max pressure recorded was 7psi. Most of the time it was around 5psi. When I reved it to 4000 the pressure increased from 5psi to 7psi. The pressure fell back to 5psi after letting it idle for several seconds. This makes me believe the spike is due to heat or pump surge. I rented the tester from autozone. I had to use an "import" adaptor to get it to fit on my car. I'm not too confident in its ability to seal so I may try this again with different equipment. 2. I gave into peer pressure and bought a new pressure cap from Autozone. I will install it today and report back. 3. I drove around for a hour yesterday off boost and am going to check to see if the system built pressure when I replace the cap today. |
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