gxl90rx7

iTrader: (1)

so ill start from beginning.. i have been running straight water and a little bit of kool-it (similar to water-wetter). it has been running really great, recent rebuild, did two 2-day track weekends with no problems running hot.

a few weeks ago, the car was completely cooled down, and I take my radiator cap off to check the level and it sprays me in the face, like somehow it was left pressurized. i checked the cap and the spring still worked fine and didnt feel stuck. so that was strange

fast forward a few drives and it randomly overheats on me.. i hyper-mile it home and change the thermostat (mazmart's 170F deg t-stat) and did the mazmart waterpump upgrade while i was in there. refilled with straight water and a little water-wetter. started it up and burped the coolant a few times. took it for a drive and it slowly overheated again

let it cool down, and again the coolant was still pressurized when i tried to remove the cap a few days later.. i had a towel this time. i released the pressure then put the cap back on.. a few days later, took teh cap off again and sure enough the pressure was back, and some more coolant spilled out, even though it had not been through a heat cycle since last time, and it did it a few more times after that. its like coolant is teleporting into the engine somehow

just now i started it up and let it just idle, and it slowly got up to 205F, fans turn on, temps still climing, they get up to about 208F.. then it suddenly spikes to 230F on my haltech, but factory gauge reads fine. I cut it off for a few minutes, restart, and temp is back down to 215F and slowly dropping, seems to level off at 210F with the fans going full blast, which is not normal. usually fans cool it down to 195F within like 10-20 seconds

soo.. wondering why it is still overheating. the radiator gets really hot, so i know its not clogged. e-fans turn on as they should. im assuming the t-stat is opening since the radiator gets hot.. what i dont know is if it is properly sealing the bypass hole, but other people running this t-stat no problems..

it could be coolant seals, but i get no exhaust smoke, and it starts up perfect, doesnt run like water is in the combustion chambers. a steady stream of bubbles come out of the overflow bottle, but only when it gets hot. no air bubbles at all when warming up. It actually did this every since i rebuilt the engine, i assumed it was due to running pure water and maybe it was boiling in the engine

anybody have problems running pure water? is coolant required to raise the boiling temp to allow cooling?

or maybe am i in coolant seal failure denial and grasping for straws

OG BBF

Hey, sad to hear of this issue bro.

Running water wouldn't cause this issue, to be certain you could flush the coolant system and run a 70 30 mix of coolant just to be sure.

If it is your coolant seals which your hoping it's not, best thing to do is A) take it to a garage and have them put the emissions probe over the coolant fill neck or radiator fill neck (with caps off of course) if it detects a high hydrocarbon prescence then your coolant seals could be gone. B) snap on do a special liquid that can detect hydrocarbons In coolant. You take a sample of coolant and put some drops of this fluid in, it'll change colour to indicate whenther coolant is ok or contaminated.

Also a 1.3bar pressure cap can cause this issue, just a thought. But to be honest could be the seals on the way out.....I hope I'm wrong....but exhaust gases in the coolant system does keep the cooling system pressurised even when cold.

As I said I hope I'm wrong, do the hydrocarbons check to rule that out, if the results are good then you can rest easy and continue trouble shooting.

Gilgamesh

If the coolant seals were going out i would think that the car would not hold coolant pressure for days because it would be leaking into the housings and out the exhaust.

I used a cooling system pressure tester recently and my car held pressure OK, it would loose a few pounds overnight, but i thought it was nothing serious.

Then i took off my wastegate and coolant poured out.... thats when i knew lol.

adam c

iTrader: (2)

The first issue seems to be overheating. If your fans are working properly, the car wont overheat at idle unless you dont have good coolant flow, or coolant level is low. Lack of flow could be a bad water pump, bad t-stat, t-stat installed wrong, or some other blockage. Since the car was running well, my first thought would be bad water pump.

Since the car holds pressure in the coolant system, I think your coolant seals are ok. It shouldnt be pressurized after complete cool down. This makes me think that your overflow system isnt working properly. Make sure you have the proper caps (in the proper places), and that your overflow lines and tank are in good working order.

You need to have some coolant in your system. Just running water will lower the boiling point too much. Probably 30% coolant is the minimum.

IRPerformance

iTrader: (41)

I don't recommend running straight water. Coolant protects the motor against corrosion and lubricates the water pump bearings. Water wetter and similar products have been known to eat coolant seals. I would go 80% distilled water and 20% traditional green coolant. If it gets cold in the winter you will need to add more coolant. What is your setup like? Radiator, intercooler, bumper?

mdp

With just water and a 0.9 bar radiator cap your coolant boils at just 246 F. The stock fan system turns on medium at 226 F. Back in the early days water and water wetter would work, but unless the coolant was religiously replace over the last 22 years (trust me it wasn't) there is probably a good build up of crud on the cooling chamber walls inhibiting heat transfer. One other thing to keep in mind is there are two coolant sensors. There is the one the ecu uses to determine the overall average engine coolant temperature, it is located so the temperature from all the coolant passages is measured. This sensor does not tell you the temperature of the most critical cooling passage. That sensor is located at the end of the coolant passage that passes between the leading and trailing spark plugs. This passage cools the hottest part of both combustion chambers. If this coolant passage over heats bad things will happen. It will give you the earliest sign of overheating long before the ecu temperature sensor indicates a problem. This sensor is connected to the temperature gauge on the dashboard. If you want to know what is going on in that cooling passage you need to either replace stock system with an after market gauge and sensor (in the same location) or use my now 20 year old instructions on "How to Linerize the Third Generation Temperature Gauge"

Sgtblue

iTrader: (16)

Agree on straight water not having enough corrosion protection and lubrication. Interesting what you said about the Water Wetter stuff. I lost a coolant seal about 6 months after adding it. Was always a little suspicious about it and never added it after the rebuild. Never really saw any significant cooling from it anyway. But never heard a experienced builder like yourself recommend against it so I figured it was just me. Car had almost 90k on it anyway.

Not sure this is even possible, but could the OP's symptoms be a result of how and where the failure of the coolant seal occurred? If the seal failed in the manor of a one-way trap door, allowing pressure from the compression cycle to pressurize the system... but then slamming shut to hold that pressure in? Just thinking that would explain air in the system with temp spiking and bubbles in the overflow, but no coolant being burned. I could also see it explaining why the cooling system remains pressurized even when cold.

cewrx7r1

iTrader: (2)

I have been running 25% Dex-Cool, 75% distilled water, and 1 bottle of Red Line Water Wetter
since the 90s without any problems. It is changed out every other year. Works great.

But to really cool the best, one needs a great radiator. The stock one is crap! The "N Pass" Koyo is one of the best!

Also running a stock setup with air filter and battery is another Mazda looser design!

Speed of light

iTrader: (8)

Yes, it is entirely possible and not a stretch to say probable--unfortunately.

Another thing to keep in mind (and bolstering the coolant seal leak theory) is that some of those combustion gasses are readily soluble in water so with even modest pressure can dissolve into and be held in a solution with H2O. When the cap is removed and the slight holding pressure released, gasses will, over time, escape the solution. This effect is analogous to opening a carbonated beverage.

rx7+8=nice

iTrader: (1)

I'm here cus I wanna know what are reg temps suppose to be under?

gxl90rx7

iTrader: (1)

mine normally runs 185-190F

btw i replaced the mazmart 170F t-stat with one tack-welded open (closing the bypass port) and it doesnt overheat at all, runs fine even in boost. pressure build up is gone too. hoping it was a defective t-stat

rx7+8=nice

iTrader: (1)

I'm glad u fixed the heating issue can u post piks of what u did? I've had temps go from 190-210 jus at idle, it is bridge ported and idles at 2000 rpm but I still think temps are high for idle. Once I'm cruising they go down to 190

gxl90rx7

iTrader: (1)

fans work?

rx7+8=nice

iTrader: (1)

Yea they come on.

IRPerformance

iTrader: (41)

All 3 speeds?

rx7+8=nice

iTrader: (1)

Didn't get to check it, it's over at addicted performance now so they'll be checking...

rx7+8=nice

iTrader: (1)

Where did you get the thermostat welded open?

gxl90rx7

iTrader: (1)

i just pulled it open an tacked it with a mig welder haha. its just temporary, i ordered an OEM to try, should be here tuesday

rx7+8=nice

iTrader: (1)

Does removing the thermostat require dumping the coolant?

ItalynStylion

iTrader: (1)

This exact thing happened to me two years ago. I had a seal failure on the combustion side. It was still largely in tact such that coolant wouldn't make its way IN to the combustion chamber and it would hold 18psi on a coolant compression test for days. However, the result of combustion is WAY higher than 18psi and would blow by the seal with ease causing air to get into the cooling system. These bubbles would push coolant into the overflow tank. However, when the system cooled, it wouldn't draw the coolant back into the tank. Whoever suggested a hydrocarbon test in their above post was right to do so.

Seems like the OP posted it was a defective tstat though. Good to hear.

One thing I find VERY strange that no one else seems to have commented on is how his system seems to build pressure AFTER the car has totally cooled and he relieves pressure by opening the cap. That's mind blowing. How it's doing that without a heat cycle is very odd. My only guess is the car isn't totally cool when he opens the radiator cap the first time.

Speed of light

iTrader: (8)

I did speak to this, see post 9 above. When this happens, it's likely the result of dissolved gasses.

ItalynStylion

iTrader: (1)

Oh, I'd missed it. Excellent explanation!

gxl90rx7

iTrader: (1)

i think i do have aslow coolant seal leak. i think air was getting trapped behind the t-stat, causing the overheating.. the open tstat lets the air out the overflow bottle. i just replaced the tstat with a normal stant, but drilled two bypass holes in it to let the air past, seems to run ok no overheating, but do get bubbles out the overflow tank. im going to run like this a while until i feel like rebuilding


btw the mazda tstat is really shitty quality. that mazmart tstat seems to be the same unit but modified. the stant is way better quality and $22 cheaper