Yes, just above the sensor. That's why it was weird. The AST was full as well.

 

So I am lost now (again).

Just checked the expansion tank. The coolant level continued to drop to about half way from where it was when I shut it down. Conclusion, coolant is being drawn back into the system???? It went up, it went back down. Just not all the way down, there is more coolant in the tank than when I started out.

Open the water neck/thermo housing. Empty down to the sensor. You can see the top of the sensor. AST is down about an inch from when I left.

Others have mentioned their thermo housing is always full. Mine has never really been full under normal operation, I always have to look down to see the coolant.

As soon as I shut the car down, I hear a gurgling coming from near or under the intake manifold. Like percolating. Another observation is usually when I pull away from a stop I can hear the coolant (and maybe air) being pushed through the heater core. Both of these things have occurred since I have owned the car. (Nov 2014)

I burped the system a number of times. And I figured any residual air would be taken care of by the AST, since that's what the name implies.

What do I do now? Top off the system and repeat the cycle?

 

What kind of AST do you have?

Coolant tends to boil near the exhaust sleeves on shut down. One of the side-effects of mazda putting a 13psi cap on the system after the recall.

 

Aftermarket alum. Bought it new in the FS section. SR motorsports maybe. The cap says 16v with no other markings so it could be a 16lb?

 

That probably is a 16psi cap.

If it's anything like the Pettit AST.... mine would allow antifreeze to flow freely into the overflow tank as I poured it into the filler cap on the engine. Tried a different pressure cap, same problem. Deleted AST...no more problem.

Some of the ASTs with a billet cap flange are much less problem-prone.

 

Personally I'm a big fan of Evans NPG+ with a zero pressure cap..... that's not easily converted to but worth discussing next time we meet up

Consider bringing it by IRP for Mr. Huk to take a look.

Silly question, but have you ensured that all your coolant hose clamps are tight?

 

So here is a pic of the setup. I know if I fill the thermo neck to the top the coolant travels over and fills the AST if the cap is off.

When I bought the car I knew nothing about FDs, it had the AST deleted and the expansion wasn't even plumbed. So I figured I would go back to as close to stock as it could be.

Just drove it about an hour or so. Topped up the thermo housing before I left. It took about 7oz of coolant. Stopped once for about 15 mins for ice cream.

Just pulled it in. The expansion tank now has another inch of coolant in it, so its roughly 3 inches higher than when I started 'logging' it yesterday. Once it cools I assume it will drop, but either way I now have probably close to 16-24oz of fluid in that tank that wasn't there two days ago.

 

Did almost every cooling hose this winter (skipped the TB hose). They are all tight. I have no visible leaks that I can find nor any coolant on the ground. Unless there is some tiny spot where its leaking and evaporating instantly say on an exhaust mani. But I would think I would see steam and/or smell it. Like when my rad almost blew at your shop this winter. LOL

I will be at IRP as soon as we can coordinate our schedules. I need to have him look it over in case its something really obvious I am missing. Also going to have him pressure test the system.

I read a few of the evans threads on here. It didn't seem like an overwhelming amount of people thought it was best for these engines.

Thanks for hanging in with me everyone. Clearly these cars are not for the faint of heart. I am only 7 months into this odyssey.

 

Checked the tank this morning. Coolant was once again drawn back into the system. But just like the last cycle, there is more coolant in the tank than previously. And the thermo housing was empty down to the sensor. Pretty much the exact results from the day before. So I have to assume if I add 8oz per cycle it will keep accumulating in the expansion tank and eventually overflow.

I have the parts to eliminate the AST so that may be my next option.

 

Have you tried replacing the pressure cap? Cheap part that essentially controls flow to and from the reservoir.

 

if it pushes coolant out, but doesn't pull it back in, you probably have a leak somewhere, and it just needs to be big enough to bleed away the vacuum. i'd say pressure testing of the system is in order

 

So Ihor pressure checked the system today. No obvious leaks. A small weep at the the rad from the AST to rad line. We tightened the clamp up. When I started it up after the test there was no smoke from the tailpipe. So he is not 100% convinced its a coolant seal.....yet.

I have the correct FC cap/neck piece to eliminate the AST so I may throw that back on.

My expansion tank is overflowing now and the system is low in the AST and the waterneck.

On a side note, when I bought the AST I had it shipped to a family member where the car was at the time. The fittings were not properly welded so we asked for a second one. Who knows, maybe the AST is the issue.

 

The leak at the bypass hose to the radiator looked enough to be a culprit. Let me know if tightening it makes any difference. As we discussed I would eliminate the AST. I see it as just another failure point (more hoses), clutters up the engine bay, and it really doesn't do anything as long as you know how to get the air out of the system after replacing the coolant. We never really run them on builds unless a customer insists on one. Get a new oem .9 bar radiator cap. I'm not a fan of the higher pressure caps.

 

What the best way to cap/block off the lower center rad fitting? Piece of hose with a plug in it?

 

No just leave that alone. Run the hose from the ast delete filler body to the overflow. The hose right below that on the actual thermostat cover goes to the small nipple on the radiator. If you want to eliminate that it really should be welded. Caps/plugs fail over time.

 

Thanks Ihor. That was my bad, if I had gone out the garage to look first before posting I would have realized I was going to have another line to plumb and not need to plug anything.

 

sounds pretty straightforward to me...

if it holds 13psi and doesn't bypass the cap and push coolant into the overflow(faulty AST or AST cap) then the system is being overpressurized. a faulty coolant seal won't always allow coolant into the engine.

course if you want to verify that, common sense sais to install the tester onto the engine while running and see how high the pressure it builds is. the gurgling should have already given you the hint, it's not super complicated.

 

I guess an update of sorts. Removed the AST and the first short run seemed fine. The next night drove it longer and then things started to go south. Coolant buzzer came on so I headed straight home. Overflow tank was overflowing and there was coolant all along the bottom and side of the car. So a rebuild it is I guess. Sucks. The upside will be starting with a fresh rebuild that can handle future mods.

Hope to pull the motor in the next few weeks while I come up with a plan for the rebuild.