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...The Pettit AST's are kind of crap. I've never been pleased with them. Either look at AST elimination or get a better one. I think that's going to be the root of a lot of those problems, even if you half way fix it now it's going to bite you again down the road.
Dale
I've had my Pettit AST since 2004. Works as it should and except for the cap issue I mentioned above, it's been fine. I do have it mounted on rubber grommets to prevent any possible cracking at the brackets - learned to do that on my racecar.
The problem with Pettit AST's is their quality has been inconsistent over the years. There are some good ones out there and some bad ones.
The biggest problems are the Lev-R-Vent caps they come with are hot garbage. Even past that, the stamped neck isn't well designed, better AST's have that part cast or CNC'd.
Also the nipples on the AST are too small (probably inch sizes in a metric car) and you have to clamp the hell out of the 2 hoses to the AST for them to seal.
Again, some are better than others, but I can't recommend them.
Fits great, uses OEM radiator caps, quality product. Also the Figher's Garage AST if you can find them, that was my design, they haven't been made in 10+ years.
The RE-A part can be obtained through RHD Japan, I'd link it but their site is down for maintenance. I think it's around $200.
All that said, the RP part should do well and it's available in the US with fast shipping.
Small win today, I tested the pressure through the ast, and my system has been holding 16psi no problem for the last hour or so with no pressure drop at all.
this tells me that either my ast is warped or otherwise not sealing, or I have two bad caps.
Can anyone ID this ast just to make sure? I’m holding the cap that was on it when I purchased the car. Please excuse the rust buildup hahaha
Okay, so I apologize for partially wasting some of your time. I realized that I was not fully installing the new cap onto the ast. Because the new spring was so stiff, I realized I needed to push down quite hard in order to achieve full lock. There was still about another quarter turn to go.
Once I installed the new cap correctly, I pressurized the system through the filler neck again. The system held about 12psi for an hour or so before I depressurized it. The cap is rated for 16psi, though. I did also notice the overflow tank bubbling when I pressurized the system above 12psi, and the bubbling slowed to a stop once the system reached about 12psi again. I did not notice this symptom while pressurizing through the ast. My previous test told me that the system will consistently hold 16+ psi for an extended period of time, so I’m assuming there is still some sort of sealing issue with the ast.
After I completed this test, I went ahead and took the car for a short drive. I did not notice any sort of temperature fluctuation. I made sure to get into boost as well as low speed driving and idling. HOWEVER, once I returned home, pulled into my garage and shut the car off, the car began to leak coolant from the overflow tank. My question is, provided the information with the second pressure test only holding 12psi indicating a small sealing issue with the ast, would this cause the system to be unable to draw vacuum to pull coolant back out of the overflow? When it comes to issues regarding my cooling system, it’s difficult to not be paranoid about coolant seals
I was doing some reading in another thread, and found that someone had suggested to pressurize the system to 20psi and let it sit overnight or up to 24hrs to check for any small leaks. I pressurized my system to 20psi through the ast last night, and at that pressure level, I heard air escaping from the cap on the filler neck (no spring). I watched the pressure decrease from 20psi to 17psi in a matter of minutes, but I decided to leave it overnight and see what happened. went and checked first thing in the morning, and the pressure had dropped all the way to 5psi. I pumped it back up to about 15psi and let it sit for the rest of the morning before I left for work. Went and checked about an hour later and the system was still at 15psi. Perhaps 20psi was just enough to break the seal in the filler neck cap and allow the air to leak out?
Just to sum up so far:
When pressurizing the system through the ast, it will hold 15psi for an hour or more. When pressurizing to 20psi, air escapes from the filler neck cap and leaks out.
When pressurizing through the filler neck with a 16psi spring cap on the ast, the system will only hold about 12psi. I let it sit in this scenario for about an hour and it didn't seem to lose any additional pressure.
When driving the car after burping the system, the car maintains temperature, but leaks water from the overflow after turning the car off
When I get home from work, I'm going to pull one of the spark plugs and check for coolant, since the cooling system had been pressurized for so long.
...My question is, provided the information with the second pressure test only holding 12psi indicating a small sealing issue with the ast, would this cause the system to be unable to draw vacuum to pull coolant back out of the overflow? When it comes to issues regarding my cooling system, it’s difficult to not be paranoid about coolant seals
I think your assessment of the system issues may be correct. Since 2 caps exhibited the same symptoms, I have a question: are they both the lever release type? If they are that could be the issue, similar to what I found with that type of cap.
o So my 1st course of action would be to get another cap of the same dimensions and pressure rating, but plain top w/o the lever and see if that works correctly.
o If that doesn't fix it, then with a magnifying glass, inspect the inner sealing diameter of the AST for any flaws (pitting, scratches, etc.). If you find any, take a piece of fine emery cloth or similar and gently sand that surface going around in a circumferential direction until they are gone.
o IMO, if that doesn't work, then my next step would be to replace or eliminate the AST.
I don't think your symptoms are indicative of a coolant seal issue.
I think your assessment of the system issues may be correct. Since 2 caps exhibited the same symptoms, I have a question: are they both the lever release type? If they are that could be the issue, similar to what I found with that type of cap.
o So my 1st course of action would be to get another cap of the same dimensions and pressure rating, but plain top w/o the lever and see if that works correctly.
o If that doesn't fix it, then with a magnifying glass, inspect the inner sealing diameter of the AST for any flaws (pitting, scratches, etc.). If you find any, take a piece of fine emery cloth or similar and gently sand that surface going around in a circumferential direction until they are gone.
o IMO, if that doesn't work, then my next step would be to replace or eliminate the AST.
The cap that originally came on the car was a lever type cap, as pictured above. This one did not hold any pressure. The replacement cap that I got from the parts store was not a lever type cap. This was the cap that held 12psi, even though it is rated for 16. I'm going to order a new unsprung cap for the filler neck since I seem to have found a small leak there as well. I'll check both surfaces for any flaws and gently run some emery cloth over both surfaces for good measure and pressurize again.
I was doing some reading in another thread, and found that someone had suggested to pressurize the system to 20psi and let it sit overnight or up to 24hrs to check for any small leaks.... Just to sum up so far:
...When pressurizing through the filler neck with a 16psi spring cap on the ast, the system will only hold about 12psi. I let it sit in this scenario for about an hour and it didn't seem to lose any additional pressure.
When driving the car after burping the system, the car maintains temperature, but leaks water from the overflow after turning the car off...
The fill cap, although not technically a "spring-type" cap, does rely on flex of the Belleville-type spring behind the rubber seal to seal properly. As such, that spring also will release pressure when its limit is exceeded, and 20 psi might just have been over its capability. It is still a good idea to replace it to eliminate any worries about it.
The fill cap, although not technically a "spring-type" cap, does rely on flex of the Belleville-type spring behind the rubber seal to seal properly. As such, that spring also will release pressure when its limit is exceeded, and 20 psi might just have been over its capability. It is still a good idea to replace it to eliminate any worries about it.
I appreciate all of your information and advice. I will update accordingly
Of course that is possible...not my 1st suspect, but possible.
Also another thought - it's possible that the rim of the filler neck may have a small flaw, so check that area along with the others.
Sorry for the delay, I was out of town for the holiday weekend. Last night I cleaned up the inner sealing surface of the ast, and pressure tested it through the filler neck. The system held 15psi this time as opposed to the 12psi experienced before the cleaning, so I think that definitely helped.
The only thing I still need to figure out is why the car leaks coolant from the overflow tank after I shut it off. I'm not sure if perhaps, the previous owner just overfilled the tank? It is significantly above the full level, and has been since I got the car. The coolant in the overflow is also bright green as opposed to the rust-colored distilled water in the system. I figured with the ast leak fixed, the system should be able to draw coolant back into the system from the overflow.
...The only thing I still need to figure out is why the car leaks coolant from the overflow tank after I shut it off. I'm not sure if perhaps, the previous owner just overfilled the tank? It is significantly above the full level, and has been since I got the car. The coolant in the overflow is also bright green as opposed to the rust-colored distilled water in the system. I figured with the ast leak fixed, the system should be able to draw coolant back into the system from the overflow.
If the system is full, then there won't be much, if any, coolant drawn back in from the OF tank when it cools. So your guess may be correct, that the tank was too full from the start.
If the system is full, then there won't be much, if any, coolant drawn back in from the OF tank when it cools. So your guess may be correct, that the tank was too full from the start.
I'm assuming that the tank was either overfilled by the previous owner, or it was having trouble evacuating coolant back out of the overflow due to the leaky ast, which caused it to fill. I'm just going to pull the overflow out, clean it, and refill it to the proper level this week when I flush the system one last time and change the thermostat. I will update after I do that and drive it. Thanks again for the help and promptness of responses.
So I have been driving the car quite a bit for the last few days. I have not noticed any overheating issues. However, I did remove the overflow tank, cleaned it, and filled it to the proper level. I’ve since driven the car a couple of times, and I’m still getting coolant leaking out of the overflow tank after shutoff after every couple drives. I fill and burp the system and I can drive it a couple times, then the issue repeats. I also checked the overflow level and it was significantly above the level that I had filled it to. It still seems to me like the system isn’t able to evacuate coolant out of the overflow after shutoff. Next I’m going to thoroughly inspect the line from the ast to the overflow for leaks. That is my next suspect. Any additional input is appreciated
The hose going from the AST to the overflow tank has to be air tight - if it has even a pinhole leak the system can't pull coolant back from the overflow tank.
Coolant heats up, expands, pushes against radiator cap and pushes into overflow tank. Coolant cools down, it contracts, and sucks the coolant from the overflow tank back into the engine. If there's a small pinhole leak or anything in that hose the engine just sucks air in through the hole and the coolant stays in the tank.
You can also have a similar situation with a bad radiator cap.
Thanks, Dale. Both radiator caps have been replaced as well as the sealing surfaces of the filler neck and the AST cleaned. The system holds pressure now, so I'm betting there's a leak in that line.
