So Im 95% certain its a coolant seal issue but a bit curious if theres something Im Missing.

94FD, 39k miles. Sat for roughly 10 years in climate controlled storage with only periodic starts with no real miles in that time.

It had a nasty leak when I got it, but was weird corrosion on the water pump and housing. I replaced with new housing, thermostat, pump, radiator, AST, and hoses. She starts up great everytime hot or cold, but when bleeding the coolant with a lisle funnel, after it warms it it will push the fluid out and maxes out the funnel. I uses a block tester and that was negative, I was hoping that to be definitive but is what leave me second guessing.

I ran a few miles just to see how it would act, I was expecting it to push coolant into the overflow tank at the same rate but it did not appear to, granted I didn't push it. Temp gauge did end up climbing about 3/4 of the way.

Is it possible this is just a nasty air-lock of sorts? I removed the throttle bottle line and coolant had reached that. The heater is blowing warm air but seems much cooler than I would expect.

Have a rebuild kit coming but figured it wouldn't hurt to check here before I tear into the block.

 

Sounds like you just may need a good bleed since your heat isn't that warm. If you are 3/4 on the temp gauge, assuming it is reading correctly, the air should be pretty hot from the heater core unless you have a blend door issue as well. It will expand quite a bit when bleeding with a lisle funnel and poor over if you keep the level high before it warms up. You may want to jack up just the font end to elevate the front to help get air bubbles out of the heater core etc. while bleeding.

You said you used a block tester and it was negative? Does this mean you pressurized the system and it did not bleed down?

If it sat for that long with coolant in it, there is a chance you have some nasty build up somewhere that is not helping with the bleeding process.

 

it is a brand new temp sensor so I would imagine its accurate. i did a pressure test and it did lose a bit of pressure over time, but from what I read that can be normal, I also used a block a tester that detects for combustion gases in the coolant and that was negative.

I also did try a the funnel with the front end jacked up as well.. hmmmm.

Oh and another weird thing I forgot to mention when I drained the block coolant at first it dribbled out, then after filling I drained again and it drained as normal. The coolant that came out all looked normal as well. Maybe Ill keep running it a bit and see if anything changes. Its a bit odd all around

 

Does AST have the correct cap?

 

Its a brand new unit from Pettit, 13lb cap

 

Try an alternate ast regardless.

 

If you have a coolant seal leak, would there not be evidence of that in the oil or in the exhaust?

Or on the ground?

 

Thats where I'm not sold as Id expect a few more issues. I did speak with Dave over at atkins and he said its possible one of the irons failed and is a mix of blocking passage as well as building up pressure which would make sense, Id expect it to boil over in the overflow if that were the case and it does not appear to be happening. The engine starts and runs fantastic besides a high idle.

I have the OE cap I can toss on and see if it makes any difference.

 

Depending on how fast the pressure dropped, that is not normal. Did it smoke more than usual after the pressure test or smell sweet like coolant. If the pressure drops like that and you can't find the external leak, it usually means it went into the combustion chamber. The fact that you had an issue draining originally points to probably more crud in some areas. Possible some of the cooling jackets in the rotor housings/irons could be blocked partially creating air pockets.

 

Hasn't smoked at all, very faint sweet smell from the exhaust on startup.

 

That, to me, indicates early mild signs of coolant seal issues. But since it's running OK, and not losing much coolant, you can run it as is as long as you monitor the coolant and other symptoms closely. Just be conscious that at some point it could progress quickly, and at that point you will need to correct the issue soon or risk damaging internals too much to reuse.

 

The ecu would usually drop the revs once the engine warms up. I might not be getting a reading from one, or more, of the water temperature sensors.

 

It tries to drop the RPMs but am assuming a vacuum leak keeps it from settling, I have all new lines I am going to repalce, they are currently like glass and broke a couple already even.

 

[Hopefully this post sets you up for a great new year.

^^^Listen to this man right here

I had the same issue as you. Exactly as you describe it and it turned out my brand new AST wasn't sealing properly and was depressurizing. So in turn, the car would dump coolant into the overflow tank when warm (like it's supposed to) but would fail to siphon it back up when cold.

This was my route. Replaced the hose did nothing (I was hoping the hose had leak/pin size hole), replaced the cap several times and it would get better for like a week or so then it would go right back to how it was. Basically proving that my issue was related to the seal between the AST and its cap. What ultimately fixed my issue was when I deleted the AST altogether.

 

I have a Pettit AST and along with some other radiator caps that had similar issues to yours, had just the slightest bit of roughness on either the pressure seal or the cap upper seal metal surface. A little polishing (in a circular fashion) with a fine emery cloth fixed all of those issues, allowing those caps to function correctly.

 

interesting, Ill look closer at it. I have the original AST I can swap out easily enough as well

 

By metal surfaces I should have clarified that I mean the seal seating surfaces on the AST in your case and/or, in general, on the radiator/fill location itself.

 

Do a coolant system pressure test. I've posted about it in the past if you want to search.

Coolant seals are the most commonly misdiagnosed thing with these cars....

 

just did a pressure test and checked out okay. Also took the plugs out and turned it over and that also checked out, not a drop of coolant.

i tested the thermostat as well just for fun and works just fine. Compression test was also good.

i am starting to think it really is a bad air lock. I have a vacuum fill kit coming tomorrow. It will get hot and when i turn shut the car off you can hear loud bubbling in the system, the heater still does not produce any heat.

 

Loud bubbling is an indicator of hot spots, maybe caused by poor coolant circulation. What kind of thermostat do you have? The OE stat is made to let coolant circulate inside the block and through the heater core before it opens. Many aftermarket ones do not, and if you have one w/o the bypass, that could be the cause of your issues.

 

I believe its OEM, I bought the complete housing/pump/thermostat kit through Mazdatrix that had it all assembled already so I did not buy it seperatley.

 

I have a favorite saying: Don't assume anything because it'll come back to bite you in the butt.

 

With the upper filler cap off can you see the coolant moving?

Can you feel if the pipes on the firewall engine bay side leading to the heater core getting hot at all?

 

Have you confirmed that the fans are running? The engine bay is tight and the front bumper opening is small, the cooling fans are doing a lot of work. Does the car have the factory undertray? Without the undertray these cars are known to overheat.

Assuming both those things check out, I would order a new radiator/AST cap. The factory radiator cap for a 2000 Toyota Landcruiser is the same fitment as our RX7 but slightly higher pressure relief spring, which can help raise the boiling point by a little bit. The factory ECU doesn't activate the fans until the engine gets pretty hot, if your radiator cap isn't holding pressure that could explain the boiling coolant. I would also run some Thermocure through the cooling system in case there is rust clogging some of the coolant passages in the engine. They say it works best if you run the engine for a while, but I would do short idling sessions (not long enough to overheat) instead. Then when draining the coolant, be sure to remove the block drain also. Just draining the radiator still leaves plenty of coolant in the engine.
While the radiator is empty, I would remove the thermostat and test it in a pot of boiling water. The thermostat for these cars is a little complex, it has both a regular opening that opens to let coolant go out to the radiator and also a secondary part that extends to block off the bypass passage that would recirculate coolant back through the engine.

I would also drill a very small hole (similar size as the jiggle pin hole) in the thermostat so there is another method for air bubbles to escape before the thermostat opens. Be sure the jiggle pin is near the top of the thermostat housing when installed, that's how it is supposed to work. When refilling coolant, pour slowly to avoid trapping air in the system.


Edit, my car's original engine lost a coolant seal, some of the early symptoms I remember was the low coolant buzzer (from slowly losing coolant) and the sound of air pockets or rushing water through the heater core. I never tested for exhaust gases in the coolant, but if I let it run for a long time it would spit coolant into the overflow tank and then overheat. The spark plugs would get wet and it would idle badly for a few seconds after starting. I don't remember much steam or smoke in the exhaust, though.

 

Saga will be continued at a later date.

Decided to replace the vacuum lines and broke a solenoid while doing so, good times.