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Trying to find out if coolant is leaking from an internal seal into the spark plug wells. Do I need to turn the engine over by hand after the system has been pressurized at 20 psi for a while? If so, how is this done? Clockwise or counter-clockwise? Any info appreciated.
A little more background: my car is mechanically stock, it has 19k miles and I bought it last year. Ever since I got it, it has had an issue with coolant overflowing out of the overflow reservoir onto the ground after shutting the engine off. This happens maybe once every 5-10 drives. It seems that coolant is not being sucked back into the engine from the overflow reservoir.
I have inspected for external leaks and didn't find any, also tested the filler neck cap (good) replaced the AST cap with the updated .9 bar version (which it already had). I have burped the cooling system many times with a Lisle funnel, heat on, throttle body coolant hose disconnected, front of car elevated, etc. I do not think there is air in the system. The car will be fine for many drives and then I will look after parking and it will be puking coolant from the overflow.
Recently, the problem seems to have gotten worse where the coolant light will turn on despite the coolant being apparently full, and the car will start overheating. I'm thinking the cooling system is not getting pressurized due to a leak somewhere, which is causing the coolant to boil and also not return from the overflow reservoir. I'm really hoping to find out something with the pressure tester.
I would say with 80% confidence you have a bad coolant seal in between your rotor housing and iron. I have dealt with this many times on my car. I had the same symptoms that you are having at around 68k miles on my original engine. The problem starts off really small and then like you are saying it gets more and more frequent until the car is undriveable.
I had replaced every coolant component on my car aside from the heater core and I mean everything, all hoses, caps, water pump housing, water pump, and radiator. I pulled the engine and sure enough I had a bad coolant seal. I had it rebuilt and only replaced the hard and soft seals in the engine. That engine lasted for one year and ~3k miles. At first it was great, kept coolant pressure, was cool in traffic, started easy every time. Then I started getting the low coolant buzzer, but wasn't overheating. Then the car was having a harder time starting and idling. I was on occasion getting a white puff of smoke on startup, but always attributed it to oil burn left over from the OMP. I bled the system using a Lisle funnel and was getting tiny bubbles. I did a coolant test and pumped it up to 20 PSI (BTW the updated 1995 shop manual in foreign markets calls only for 15 PSI). Well that 20 PSI did it in, the car would not start. I pulled the plugs on the rear housing and they were SOAKED in coolant. I pulled the engine, the new coolant seal was busted in the same place as the old one and there was a crack in the iron around the coolant jacket.
I not only would I do a pressure test, but I would also do the champagne bubble test. The bubble test can be a bit miss leading, but if you cannot hold pressure and you are getting bubbles it is a bad coolant seal.
Check your radiator fill and AST caps. If they are worn out or they are the wrong caps you will have the similar problems.
I keep hoping to find some external leak, but it being an internal seal is the direction I'm leaning as well. I just refilled the system with the Lisle funnel for what seems like the 100th time, and this is what it looked like while idling:
Anyone know the best way to check the spark plug wells for coolant? I would like to find something more definitive. Is there is a bolt at the front of the engine that is easy to turn the engine over with?
Anyone know the best way to check the spark plug wells for coolant? I would like to find something more definitive. Is there is a bolt at the front of the engine that is easy to turn the engine over with?
I would think the easiest method would be to either pull the EGI fuse and turn the starter over or jacket up the rear axel and spin the wheels while in gear. The bolt on the front of the engine you are referring to is in the center of the front crank pulley and is a pain to get to on a stock car if I recall right.
Radiator and AST are stock, everything else in the engine bay is stock as well.
I went for a drive after using the Lisle funnel this evening and got coolant spilling out of overflow reservoir a few minutes after shutting the engine off. It has done that before, but it seems to be getting more frequent. Almost every drive now...
Perhaps you have air leaking into the system somewhere? I have heard of it happening with certain radiator caps. I cannot speak to the age of the part and whether it was OEM or not.
My car did the same thing shortly after I got it at 51k miles on the original engine. Tested the coolant system for remnants of combustion with a few coolant test strips and did not find anything. Ended up pulling the old block and replacing it with a new one since I bought it to convert it.
A friend had the same thing happen with a car he bought at 45k miles on the original engine. started losing coolant through the overflow. Pulled it and replaced it to later find out that the coolant seal retaining wall on the original shortblock had failed from coolant sitting there for much too long.
This happend to me at 46k miles, it was the AST cap. Hasn't leaked since and not loosing coolant. I got the cap from Mazda. May be worth getting another OE cap just in case. Small chance but defective parts from the OE happens, I'd still get it from Mazda.
Check the hose that runs from the AST neck to the overflow tank. If that hose won't hold a vacuum, the AST can't draw coolant back from the tank when the engine cools down. That hose consists of a few sections and connectors.
They might be good enough to hold hot coolant flowing to the tank from the AST, but they might suck air instead of drawing coolant out of the overflow tank when things cool down. The result of a vacuum leak in that hose is an accumulation of overflowing coolant in the tank and low coolant in the engine. It can act just like a bad AST pressure relief cap.
Since the hose is unpressurized and is downstream of the AST cap, it is not tested when you do a system pressure test.
You also might want to inspect the overflow tank itself to make sure the the pick-up tube (that the hose connects to) is OK and runs to the bottom of the tank as it should.
Alright, little update, I did a cooling system pressure test today, pressurized the system to 15 psi (thanks @suzukisteve for the info on the updated pressure), waited 30 minutes, and it was at 13 psi. That would suggest a leak somewhere, but maybe the air was just escaping out the overflow breather hole?
Also pulled the spark plugs with the system pressurized after cranking over with the EGI fuse pulled and they were dry:
Coolant started coming out of the top of the overflow reservoir again when I cranked the engine for a few seconds with the spark plugs pulled...
Thank you Retserof, I need to check the AST to reservoir hose, it is a bit hard to access to haven't gotten the chance to yet. AST cap should be good as it is brand new OEM Mazda, also had the same symptoms with previous OEM AST cap.
No, I did it on the filler neck and it leaked down to 12 psi or so (originally I said 13, but it was actually lower). Maybe I should put it on the AST to eliminate the AST cap... since that vents at 13 psi. Thank you all for all the help.
I'm assuming the test needs to be done with the car cold, since if the coolant is warm the system will depressurize as the coolant contracts, giving a false reading.
Test needs to be done at the AST, filler neck if AST is deleted. Since the OEM cap is 13psi it will release pressure to the overflow above 13psi. I would redo the test and see.
Alright, making a bit more progress with what seems like an actual accurate pressure reading. I put the tester on the AST this time (thanks @ZE Power MX6 ), and it held 15 psi for an hour before I removed the tester. I think the pressure drop from last time was just from the engine cooling.
I'm thinking this makes the hose from the AST to the reservoir more likely as a culprit, since I believe it is the only part of the cooling system that is not tested in the pressure test (?), and could cause the overflow symptoms. That and the AST cap. As I mentioned, my AST cap is brand new OEM, so I think it is probably not that, though I suppose it could be defective.
Just to be sure, I read you're using the 13psi cap on the AST, you don't happen to be using a pressure cap on the filler neck as well by accident? It should be an un-pressurised cap (No spring, just a sealing cap)
And as you mentioned in your recent post, checking the AST to overflow hose for leaks is a good idea, if there's a small split or pin hole, it won't be able to produce suction.
Your system seems ok then, the problem is likely between AST and the overflow, whatever is introducing air during cool down. The hose is a good place to start, it has 3 sections so each joint is a potential candidate. I would also remove the fender liner to inspect the tank, make sure every connection is air tight.
I had the same issue with my Camry recently, I was losing a few oz of coolant daily after a motor swap, and they use those dumb red coolant too. Turns out the overflow tank cap was wrapped from overheating, it would suck in air instead of coolant from the tanks. It would leave a few drops at the top of the tank too, but not enough to drip to the floor and they dry pretty quick. This might also explain why you have a little air in the system when you did the champaign test.
FYI since you're new to the FD.
Various things happen to the cooling system as these cars age:
1. the rubber hoses get hard and brittle from both age and heat cycling. this causes:
- poor fitment between the hose and the barb it is attached to
- splits, ruptures, holes in the hose themselves
2. hose clamps wear out
- stock spring tension hose clamps lose tension allowing air to be sucked in under vacuum and/or coolant to be leaked out during pressure. Either or both can occur.
- non-stock worm gear hose clamps loosen up from heat cycles. highly recommend replacing them for new stock clamps.
3. plastic cooling parts (like the ast, thermostat neck and radiator) get hard and brittle. this causes them to warp, crack, break etc
Probably a good idea to switch out the most suspect hoses and clamps as mentioned in previous posts and re-test.
Just to be sure, I read you're using the 13psi cap on the AST, you don't happen to be using a pressure cap on the filler neck as well by accident? It should be an un-pressurised cap (No spring, just a sealing cap)
Yep, stock setup of normal cap on filler neck, OEM sprung cap (13 psi) on AST.
Originally Posted by ZE Power MX6
Your system seems ok then, the problem is likely between AST and the overflow, whatever is introducing air during cool down. The hose is a good place to start, it has 3 sections so each joint is a potential candidate. I would also remove the fender liner to inspect the tank, make sure every connection is air tight.
That's what I'm thinking as well. Checking and replacing the AST to reservoir hose/connections is the plan right now.
If that doesn't work, I'm going to replace the thermostat. It's easy enough to replace, and I think a sticky thermostat could cause weird cooling system issues like this.
@gracer7-rx7 I agree that having all new hoses/connections/radiator/AST would probably be a good idea. However, wouldn't the fact that the cooling system held pressure rule out leaks at the radiator, hoses, AST, etc.? I'm trying to avoid wholesale replacement of the entire cooling system if possible.
In rare cases, a cap, fitting, seal, or hose can hold pressure, but leak under vacuum. So while I agree with your assessment, anything that experiences vacuum (most of the system is under a slight vacuum while it cools down) can be the cause of air in the system.
@gracer7-rx7 I agree that having all new hoses/connections/radiator/AST would probably be a good idea. However, wouldn't the fact that the cooling system held pressure rule out leaks at the radiator, hoses, AST, etc.? I'm trying to avoid wholesale replacement of the entire cooling system if possible.
Yep. Which is why I added this at the end.
Originally Posted by gracer7-rx7
Probably a good idea to switch out the most suspect hoses and clamps as mentioned in previous posts and re-test.
When I first got my car 20 years ago, I replaced a couple of hoses as they started leaking. I eventually got tired of waiting for another issue to pop up whack a mole style and ordered the full hose kit and clamps from Ray Crowe and did them. Was leak free for years after.
The caveat to my experience is that my car had lots more mileage and heat cycles than yours so the bulk of your hoses are probably in better condition than what I started with. Right now, you seem to have identified a problem area. I'd focus on that and then re-evaluate if the problem persists.
In rare cases, a cap, fitting, seal, or hose can hold pressure, but leak under vacuum. So while I agree with your assessment, anything that experiences vacuum (most of the system is under a slight vacuum while it cools down) can be the cause of air in the system.
I have experienced this too once upon a time...
The cooling system is under pressure due to the engine running. Metal, rubber, liquid all expand when hot and contract as they cool. In the heat / expansion cycle, the metal hose barb, coolant, rubber hose will all expand. Expansion of the rubber hose will cause the spring clamp to exert more clamping pressure decreasing capability of a leak.
When you shut the car off, everything starts to cool and contract. A weak spring clamp coupled with a hard rubber hose that no longer fits as tightly as it used to can allow air to be sucked in under vacuum at that point.
10-21-22, 03:32 PM
