RIWWP

iTrader: (2)

2005, 106,000 miles on the chassis, 13,000 on the motor (mazda reman), OEM cooling system until recently.

About a month ago, I had my 8 on a trip for a week, and it regularly spent time driving in traffic at ambient temps >95F, with a peak of 105F. The following week upon returning from work and popping the hood to facilitate cooling as I usually do, I found that the return drive from work had dumped coolant out the overflow. The next day I pulled my thermostat, and stuck it in a pot of water along with a Mazmart 170F thermostat, and brought it up to a boil, watching the movement and measuring temps with an IR thermometer. I confirmed that the OEM thermostat did start opening at 183F as it is supposed to, but never got more than ~50% open, even at the 212F water boiling point. The Mazmart thermostat worked correctly, 170F start and 190F full, so I put that one in and put everything back together.

Ever since, I have a cooling system pressure issue apparently. Starting up the car and letting it idle up to temp, watching the overflow and the coolant temp, starting at about 135F, coolant starts dripping out of the overflow, increasing in flow rate as the temp increases, though not drastically. When it gets to the thermostat temp, it holds at 172F easily, but there is a tiny but steady stream of coolant from the overflow. I even grabbed 10ft of clear tubing to replace the overflow hose and ran that out of the engine bay to the driver's mirror so I could see the flow rate while driving. And I can empty the bottle to the point of getting the coolant level light triggering (validly) in about 10 miles of casual driving without hard throttle or high revs. Temp sensor is showing normal acceptable temps of 170-190 the entire time.

I did a full flush of the coolant system with a hose (>20 minutes of flush time) including full bleeding it, which failed to correct the problem. I just had the system pressure tested and coolant tested for combustion gasses, and the mechanic claims that it held pressure up to 20psi. The combustion gas test came back negative.

Side note:
The mechanic said that my "exhaust doesn't sound or smell right, so there is something obviously wrong with my engine, and the coolant overflow confirms that, so I must have lost an apex seal."


So wait, my BHR midpipe is sucking coolant out of my coolant bottle overflow, which means I lost an apex seal....?





Ok.


Not going back there again.




So about the only thing I can trust from the test is that the coolant is free of combustion gasses, so it's unlikely to be a coolant seal problem? I have sent a sample of oil off to Blackstone for testing, which should confirm it.

I guess I will take a day or two and disassemble everything I touched during the thermostat replacement, and inspect/replace. Any suggestions, tips, places to check?

Mazmart

iTrader: (12)

Radiator cap should be checked since it controls that aspect.

Paul.

RIWWP

iTrader: (2)

New cap from Advance Auto. The mechanic said it holds pressure to 20psi. Though I am not certain I can really trust him completely.

Part of me has been thinking I just have a coolant bottle and cap failure, and that I need to order the brand new set from you, but I'd rather make sure of that before I just toss you an order


(though I did JUST email you on a different topic regarding my Miata.... )

dannobre

iTrader: (3)

You sure the cap seals properly to the bottle...OEM cap would likely be better

RIWWP

iTrader: (2)

No, I am not sure

Yeah, probably need to get an OEM cap to test with. Just shipping usually doubles the price... or the dealer doubles the price without shipping, so I just grabbed one locally. Though if it's the bottle itself that isn't allowing the cap to seal, then an OEM cap won't solve the problem (though I'd just order an entirely new bottle and cap from Mazmart at that point).


I wonder if my Miata's cap is the same size and rating.... hmmmm

RIWWP

iTrader: (2)

It's 13psi too, and fits right on. Idling it warm now to see if I still have overflow.

Javii

iTrader: (1)

Goddamn that's bold.

Isn't the RX8 is 15psi?

RIWWP

iTrader: (2)

13 that I was aware of?

Got a video. There was coolant left in the long tubing, so I looped it up through the hood latch, letting the coolant in the tube sit against the overflow spout. Idling warm there was a stream of air bubbles out of the overflow for about 5 minutes.

Then the bubble flow stopped, coolant level in the tube remained steady, so once the air was done escaping, coolant wasn't.

I hopped in the car and increased the revs. The coolant level in the tube dropped as soon as I picked up the revs, and dropped again at each rev increment increase. Coolant getting sucked back into the coolant bottle. I dropped the revs back to idle and the coolant level in the tube remained at the low point that it had dropped to, but then I started to get a stream of bubbles again.

I would guess that this means that if the air in the system got squeezed out during the initial idling, increasing the revs introduced more air back into the system. Possibly a coolant hose failure that is letting air in?


Video upload to youtube seems to have stalled.

RIWWP

iTrader: (2)

And yes, it's not really 'coolant' at the moment, almost entirely water until I can get this solved. Maybe a pint of 50/50 in the system to give the green tint so I can see it more clearly. Once I have it solved, I'll reflush and increase the actual coolant %. In diagnosis it helps being able to ignore having to catch draining coolant.

Mazmart

iTrader: (12)

Chris (My Miata man) will respond to that email shortly. He will need to know things like how recently the swap was done, what coil type is being used etc.

Paul.

Javii

iTrader: (1)

Yeah you're right... 13psi I just checked mine.

dannobre

iTrader: (3)

The fish in your local creeks will thank you

RIWWP

iTrader: (2)

And my neighbors won't get upset about me dumping coolant on the ground.

RIWWP

iTrader: (2)

Update:

I left the radiator cap swap as is, and drove the 74 miles to work in the Miata using the radiator cap that was on the 8. Zero coolant loss, temps remained steady, even in stop and go traffic that extended my usual commute by an hour. So it's not the cap.

I also kept testing the 8 into last night periodically, including disconnecting all the hoses involved in a thermostat removal and reconnecting them, refilling and re-bleeding the coolant again, and the problem remains.

HiFlite999

iTrader: (2)

You might try twisting the oil fill cap open to make sure the crankcase isn't pressurizing, thus potentially forcing gas (not necessarily combustion gas) past a coolant seal. Another test would be to measure the pressure in the coolant overflow bottle. Is there any water in the oil?

RIWWP

iTrader: (2)

Hmm. I was about to say "I did that", but then I realized that it's slightly different. You are saying "determine what the pressure is in the coolant bottle", not "find out what pressure it can hold" ?

Will test the oil cap off to see when I get home.

HiFlite999

iTrader: (2)

I'm guessing the pressure is really climbing to 13 psi and the cap is opening properly. In the absence of boiling, it seems that blowby would be the only cause of that. You might also take your IR thermometer and "Survey" the inlet, outlet, heater hoses and radiator to see if the temp distribution makes sense, in case the water circulation is messed up somehow. I'd still bet on blowbuy though and a 50/50 change the bubbling stops or slows when the oil fill cap is slightly opened.

RIWWP

iTrader: (2)

Hmm, yeah, making sense. The air getting pushed out during warm up as it comes up to pressure, then getting re-introduced with climbing revs, and then getting pushed out again once it returns to a stable idle has been making me thing that this isn't a bottle/cap issue.

Sigh. I really hope it's not a coolant seal. Although if it is you all might get to see a 13,000 mile reman tear-down....

ASH8

Just so you are aware, the OE Coolant Radiator Cap N3H1-15-205 is specific ONLY to the RX-8, Mazda does not use it on any other car, I know it is not the same PN as my NC Miata, could be label, have not compared...Just throwing this one out there.

And Yes, I have seen this with incorrect 'style' of radiator cap, is the non genuine one 100% identical to OEM N3H1-15-205?

The only other thing I can think of and have seen it before even though system pressure test is OK, and that is Coolant Entry (Coolant Seal) into Engine when engine is hot at it's 'very early' stages of deterioration...sorry.

Can you remove cap (hot engine) and see IF you are getting a very fine 'string/strand' of bubbles?

ASH8

BTW, You need someone else on the Throttle while You observe coolant bubbles, hold revs at around 2500-3200 RPM for a short while and look...Good luck...I don't like the sound of this though Pearl..

Idle only, usually won't work, unless you have REALLY bad Coolant Entry...but then you would have start issues.

RIWWP

iTrader: (2)

Agreed that the caps aren't the same part number. The top part with the "handles" is a different size of gripping surface. The have the same gripping diameter and depth, and the pressure part appears to be the same. I don't think that it's a cap issue, even if I had the OEM one, since if it was a cap issue then I'd expect I'd get a failure on the Miata (NB '99).

Most of my observations right now are with the impact on coolant in the vertical tube, which I can see from the driver's seat. There IS air getting into the system when I increase the revs, though it only gets out into the tube via the overflow spout once I let off the gas.

I tried with the cap off, and I literally just get overflow out the top filler hole at idle. And most of the contents of the coolant bottle disappear into the coolant system, triggering my low coolant level light, when the revs increase. Not sure how to figure out how to watch a stream of bubbles like this.



On the other hand, I was answering a question in the Dumb Question thread, and realized that I am at 106,452 miles (wife checked for me), and I had my engine replaced at 95,935, which puts my 12,000 mile service warranty good until 107,935, so I'm still under that service warranty for another 1,483 miles

If I have indeed lost a coolant seal, I need to prove it to myself first, and then figure out how to prove it to the dealer. I seriously doubt I'd have sufficient compression loss this early in a coolant seal failure.

ASH8

You need to remove water in CB to half full, otherwise it will overflow out of top of CB.

Obviously you have to be careful when removing hot cap.

You need 2 people, one on throttle the other looking (inside CB) once cap is off for 'a' bubble string...
You have to do all this relatively fast or pressure builds up and overflows, idle is no good, keeping revs up 3200 keeps water down.

RIWWP

iTrader: (2)

The level varies even more than that Ash. Not something that I've seen an 8 do before, and I think it another indicator of the issue.

I can top off the system completely cool, and it will push enough water out by the time that it's warm that when reving in neutral to 2,500-3,000 rpm the level of water in the CB drops below the low level sensor in the bottle. I suppose I could have my wife hold it there with the cap off and me re-filling it to keep it up high enough to check.

ASH8

Jeez!

RIWWP

iTrader: (2)

The more I'm thinking about this, the more I think it IS a coolant seal failure.

Nothing else makes enough sense. I think the key point is that if all the air in the bottle gets pushed out in idle, where is more air coming from when I increase the revs?

Logically, it would have to either be A) a gas that is under a higher pressure than the coolant system, or B) there is a localized pressure drop in the coolant system to lower than ambient pressure, and it's coming in through a crack or other failure point (and doesn't spew out coolant when under pressure).

I don't see how B could happen, but someone else might. I can see a few ways A could happen, and none of them good.