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Overheating - cracked coolant reservoir?

Old 02-04-2019, 10:16 PM
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Overheating - cracked coolant reservoir?

so today I noticed my fans were running a bit longer than they should have and then my temp gauge going up. I turned it off soon after and saw that my coolant bottle was 1. Leaking from the seam around the middle and 2. Spitting it out from the overflow. Is the issue the bottle or something else like a water pump or the thermostat??

additionally, just replaced the thermostat to a mishimoto one and then just replaced the coolant at the same time.
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Old 02-05-2019, 01:30 AM
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If it's leaking from the bottle, well then it's the bottle.

Check the cap as well. These also wear with time and can't hold pressure like it used to.

If you aren't sure if there are other leaks, you can rent a coolant system tester to make sure the system isn't leaking anywhere else.
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Old 02-05-2019, 02:49 AM
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You may have also had a huge air bubble in the system that worked its way out and you couldve caused some engine damage so i would compression check your motor and then pressure check your cooling system like Jin said. Did you make sure to burp the cooling system properly?
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Old 02-05-2019, 08:23 AM
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Originally Posted by UnknownJinX View Post
If it's leaking from the bottle, well then it's the bottle.

Check the cap as well. These also wear with time and can't hold pressure like it used to.

If you aren't sure if there are other leaks, you can rent a coolant system tester to make sure the system isn't leaking anywhere else.
I may have to do that. I saw one online for pretty cheap. I ordered an aluminum one just in case. As far as I could tell none of it leaked from the cap unless I opened it and it shot out like crazy :P do you think it could be something in addition to that or possibly just the bottle?
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Old 02-05-2019, 08:26 AM
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Originally Posted by Xero Ryuu View Post
You may have also had a huge air bubble in the system that worked its way out and you couldve caused some engine damage so i would compression check your motor and then pressure check your cooling system like Jin said. Did you make sure to burp the cooling system properly?
could be! I know when I first added the coolant I didnít know I had to burp it and it smoked for a second or two. (Horrible I know. This is my first car that Iíve been under the hood a ton. Trying to DIY as much as possible to appease the wife on costs)

with the compression test, I did the unthinkable and bought the car without one, however it did not show any signs of low compression and had a fresh rebuild at ~70k. I know when I called my local Mazda theirs has been broken :í( May just have to take it over to Angel Motorsports in Chesapeake. Itís a 3.5hr drive though XP
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Old 02-05-2019, 09:33 AM
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If your coolant tank is leaking, then yes, you must, at the very least, replace the tank - regardless of whether or not you have other coolant issues.

Theyíre not that expensive. And plastic parts like coolant tanks can degrade over years of use.
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Old 02-05-2019, 10:36 AM
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Depending on what they are charging you for compression test, it might be worth just buying your own rotary compression tester and then you could check your compression as needed or every 6 months.

Also this car is not a Toyota it is not very forgiving for user error screw-ups, I highly advise before doing anything yourself to do a lot of research and have printed out procedures of what to do as well as use videos for reference in the process of doing anything you are not routinely familiar with. If you overheated the engine because it was not burped properly 1 overheat could ruin the motor
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Old 02-05-2019, 10:51 AM
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Originally Posted by Xero Ryuu View Post
Depending on what they are charging you for compression test, it might be worth just buying your own rotary compression tester and then you could check your compression as needed or every 6 months.

Also this car is not a Toyota it is not very forgiving for user error screw-ups, I highly advise before doing anything yourself to do a lot of research and have printed out procedures of what to do as well as use videos for reference in the process of doing anything you are not routinely familiar with. If you overheated the engine because it was not burped properly 1 overheat could ruin the motor
may have to get one then! From what I remember, my local Mazda dealer said that if they had one, itíd about ~200-250. I know I could get that compression tester for 300.

It was something I was unaware that needed to be done. Iím crossing my fingers and praying that there isnít any leakage into the housings. I guess I wonít know unless I get the oil tested.

Last edited by HappyTriangles; 02-05-2019 at 05:19 PM. Reason: Typo
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Old 02-06-2019, 06:58 PM
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So I changed the coolant tank to an aluminum one. Seemed to heat up a lot slower but I did notice the fans kicked in. Itís about 60 degrees and I shut it off once I saw the temp gauge wiggle past middle. I did fill with water just until I can sort out all the issues.

Is there a possibility it could be I bought a bad thermostat or it is more likely the water pump??
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Old 02-06-2019, 07:06 PM
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Testing the oil won't get you far, if coolant is entering the chamber and burning up. It's not like a head gasket.

Pull the plugs, see what the deposits tell you.

When the car was warmed up was the upper rad hose hot? If not, it's the thermostat. Check that both fans are turning.
Was this tested with car standing still or were you driving? If driving, do you still have the engine under tray?
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Old 02-06-2019, 07:13 PM
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Originally Posted by Loki View Post
Testing the oil won't get you far, if coolant is entering the chamber and burning up. It's not like a head gasket.

Pull the plugs, see what the deposits tell you.

When the car was warmed up was the upper rad hose hot? If not, it's the thermostat. Check that both fans are turning.
Was this tested with car standing still or were you driving? If driving, do you still have the engine under tray?
so dumb question, which one is the upper radiator hose? Is it the one going to the bottom of the housing for the thermostat?? If so, it was hot.

it was tested sitting still in my driveway. I know i kinda have an undertray. A little bit of it is missing

Last edited by HappyTriangles; 02-06-2019 at 09:05 PM.
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Old 02-07-2019, 07:46 AM
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I may bring it back to temp after work today to check the temp of all the hoses and turn it off once fans come on. I just figured out the upper rad house is at the top of the housing.
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Old 02-07-2019, 09:09 AM
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Spitting a little coolant out the overflow hose is normal, if you don't get the coolant level just right. Just make sure it doesn't end up on your power steering connector.

I will never understand why people put Mishimoto thermostats in their cars. It's overpriced junk that does nothing beneficial. You have lowered the FLOOR temperature of the car, when it is at operating temp. That is your cruising down the highway temp. RX-8 heat issues do not occur when cruising down the highway. The ONLY thing it may do for you is delay overheating by a minute or two, if you have other cooling system problems. Meanwhile, the floor temp is now below design spec, which probably is not beneficial.

My bets on your problem are:
1. Thermostat installed backwards. Not sure if it is possible with the 8, as it has been a few years since I replaced one, but it is possible with a lot of cars. If it is backwards, it will never open. Top hose will not get hot.
2. Thermostat installed upside-down. The bleed hole / jiggler should be at the top to allow air to bleed through the thermostat. It will not bleed if installed with the hole / jiggler pointed down.
3. System improperly burped. The proper way to burp the RX-8 is to elevate the front end and run the car through several fan cycles with the heater on and radiator cap off. Massaging the top radiator hose can help, if it isn't too hot. Keep adding coolant to keep the bottle at the full-hot level until the level stops going down. This might take an hour or more. You can elevate it by parking it on a sloped driveway or placing the front on jackstands. Elevating the front end causes any air to move toward the top hoes and coolant bottle, which is where it escapes.
4. Thermostat not opening. Top hose will not get hot. BTW, there is a difference between warm and hot. The top hose will always eventually get warm, because a trickle of hot water is running through it at all times. When the thermostat starts to open, it will get hot, as in 180F.

Do you have an OBDII scanner? This inexpensive device works with an app on your phone to show you true coolant temp, among many other parameters from the ECU. It is perfectly normal for the RX-8's coolant temp to reach upwards of 210F during the burping procedure.

Last edited by Steve Dallas; 02-08-2019 at 09:46 AM.
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Old 02-07-2019, 10:30 AM
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Originally Posted by Steve Dallas View Post
Spitting a little coolant out the overflow hose is normal, if you don't get the coolant level just right. Just make sure it doesn't end up on your power steering connector.

I will never understand why people put Mishimoto thermostats in their cars. It's overpriced junk that does nothing beneficial. You have lowered the FLOOR temperature of the car, when it is at operating temp. That is your cruising down the highway temp. RX-8 heat issues do not occur when cruising down the highway. The ONLY thing it may do for you is delay overheating by a minute or two, if you have other cooling system problems. Meanwhile, the floor temp is now below design spec, which probably is not beneficial.

My bets on your problem are:
1. Thermostat installed backwards. Not sure if it is possible with the 8, as it has been a few years since I replaced one, but it is possible with a lot of cars. If it is backwards, it will never open. Top hose will not get hot.
2. Thermostat installed upside-down. The bleed hole / jiggler should be at the top to allow air to bleed through the thermostat. It will not bleed if installed with the hole / jiggler pointed down.
3. System improperly burped. The proper way to burp the RX-8 is to elevate the front end and run the car through several fan cycles with the radiator cap off. Massaging the top radiator hose can help, if it isn't too hot. Keep adding coolant to keep the bottle at the full-hot level until the level stops going down. This might take an hour or more. You can elevate it by parking it on a sloped driveway or placing the front on jackstands. Elevating the front end causes any air to move toward the top hoes and coolant bottle, which is where it escapes.
4. Thermostat not opening. Top hose will not get hot. BTW, there is a difference between warm and hot. The top hose will always eventually get warm, because a trickle of hot water is running through it at all times. When the thermostat starts to open, it will get hot, as in 180F.

Do you have an OBDII scanner? This inexpensive device works with an app on your phone to show you true coolant temp, among many other parameters from the ECU. It is perfectly normal for the RX-8's coolant temp to reach upwards of 210F during the burping procedure.
this is very helpful!! Iím sure I installed it correctly but there is a small chance I did not. It was running for about a week without any overheating issues whatsoever which makes me scratch my head a lot. Now, it has been up to the mid 60ís and low 70ís here in VA, but I know I was pushing it to redline normally with no issues whatsoever.

I do have an OBDII but itís only a plug in that reads and resets. Pretty cheapo device. I do have a tablet I can mount in there for monitoring, which was my plan for spring when I can take it to learn drifting (may be a dumb idea, but I like an adventure).

When I burped the system I did a different way and opened up the throttle body coolant hose and one of the guys said once itís spitting coolant, itís been duly burped. Would you recommend massaging it over that way??

When I checked it, the bottom one was hot and the top part was cool. Again, Iíll check it again tonight but is it possibly something got into the coolant system and then messed but the spring in the thermostat??
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Old 02-07-2019, 07:50 PM
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So I was finally able to open the hood while reading This forum. At a certain time it looked like coolant was pushing through and both hoses to the thermostat were getting nice and hot. Also both fans turned on when I put on the AC and at temp as well

I assume at this point it’s safe to say it’s a radiator problem??

I also just read this: https://www.rx8club.com/series-i-tec...stions-259459/

A couple weeks ago i did have a p0420. could it be my cat is causing issues??

Last edited by HappyTriangles; 02-07-2019 at 10:01 PM.
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Old 02-08-2019, 01:50 AM
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The orientation of the thermostat is important to it functioning properly in our cooling systems.

You must ensure to properly burp the system. This means jacking up the front of the car by at least a foot, have your heater going full blast, and have all coolant hoses connected appropriately.

You MUST use Mazda FL22 coolant if you arent keen on alternative coolant options and mixes for your car.

You MUST closely monitor the cooling system for leaks. My advice? Get yourself a blacklight and burp the system after dark. Use flashlights if you need to see things, and the blacklight when turning the car on to check for leaks. Like most coolants, Mazda FL22 coolant glows pretty brightly under UV light, so it should be pretty easy to spot leaks when everything else is pretty dimly lit.

Also wouldnt hurt to remove and check your catalytic converter for damage so you do not risk potentially damaging your engine any further that it already might have if indeed it is bad.
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Old 02-08-2019, 07:53 AM
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Is coolant bubbling in the tank while the car is running? Since your tank had cracked, is it possible the engine overheated? If it did and a water seal failed, you would have exhaust gas going into the coolant and causing bubbles in the tank. The coolant in the tank should be still on a happy car.

Also that p0420 is bad news. Not sure it would cause the heat issue, but something to inspect for sure.

I don't think it's a rad issue, rads don't up and fail like that. But have a look at the fans. Are both turning? Are they turning fast?

​​​​​
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Old 02-08-2019, 08:27 AM
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Originally Posted by Loki View Post
Is coolant bubbling in the tank while the car is running? Since your tank had cracked, is it possible the engine overheated? If it did and a water seal failed, you would have exhaust gas going into the coolant and causing bubbles in the tank. The coolant in the tank should be still on a happy car.

Also that p0420 is bad news. Not sure it would cause the heat issue, but something to inspect for sure.

I don't think it's a rad issue, rads don't up and fail like that. But have a look at the fans. Are both turning? Are they turning fast?

​​​​​
since I installed the new aluminum tank, no bubbling that I could see. Just a nice swirl around the tank. I assume thatís what you want to see if overheating does occur. I know when it first happened on Monday, it almost pegged ( probably 7/8th of the gauge). I let it cool down and then had it towed to the house. Havenít driven it since.

When I turned it on yesterday to do a light checking over, both fans were spinning nicely without any issues I could see. There is a bit of coolant in the plastic slots (from the coolant bubbling all over), but still running and turns on at temp and when I turn on AC.

The p0420 only occurred once and so I didnít think anything of it. Only a thought of ďmaybe I could gut my cat or ask the wife to allow a nice mid pipe.Ē To me, that seems like the probable issue since I do pre-mix and the car has close to 93k miles. One forum that I posted above seemed to suggest that it can happen, but then again, I have no real idea until I open it up.

Last edited by HappyTriangles; 02-08-2019 at 08:29 AM.
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Old 02-08-2019, 09:57 AM
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You replaced the radiator too? Did you seal around it with foam like the factory radiator? If not, you REDUCED the cooling capacity of the system, as there is now less positive pressure in front of the radiator, because air is flowing around it. You need to seal the top, bottom, and cold side (driver's side in the LHD versions) to bring the new radiator's performance back up to at least the same level as the stock radiator.

Xero brought up a good point that I forgot to include in my burping procedure. The heater has to be turned on get all the air out of the heater core and hoses.

Seal around the radiator and burp it properly and see how it does. Watch it with an OBDII scanner to make sure you do not overheat it again.

Definitely inspect the cat and make sure it isn't clogging. A clogged cat WILL kill your engine.

BTW, there are very few aftermarket radiators that outperform the factory radiator, and they are very expensive.

More generally:

There are very few aftermarket _______ that outperform factory _______. Don't replace OE stuff with bling. It is rarely worth the money.
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Old 02-08-2019, 12:12 PM
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Originally Posted by Steve Dallas View Post
You replaced the radiator too? Did you seal around it with foam like the factory radiator? If not, you REDUCED the cooling capacity of the system, as there is now less positive pressure in front of the radiator, because air is flowing around it. You need to seal the top, bottom, and cold side (driver's side in the LHD versions) to bring the new radiator's performance back up to at least the same level as the stock radiator.

Xero brought up a good point that I forgot to include in my burping procedure. The heater has to be turned on get all the air out of the heater core and hoses.

Seal around the radiator and burp it properly and see how it does. Watch it with an OBDII scanner to make sure you do not overheat it again.

Definitely inspect the cat and make sure it isn't clogging. A clogged cat WILL kill your engine.

BTW, there are very few aftermarket radiators that outperform the factory radiator, and they are very expensive.

More generally:

There are very few aftermarket _______ that outperform factory _______. Don't replace OE stuff with bling. It is rarely worth the money.
havenít done the radiator quite yet. Thatís next on the list with better fans. The previous owner replaced the radiator maybe a year ago and I havenít had any issues with temps until now. I plan to go with either a Koyo or a CSF from BHR.

Iíll get pictures of my plugs this weekend and post them. Iím assuming they should be clean though since I replaced them 2k ago
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Old 02-09-2019, 10:37 AM
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Originally Posted by HappyTriangles View Post

havenít done the radiator quite yet. Thatís next on the list with better fans. The previous owner replaced the radiator maybe a year ago and I havenít had any issues with temps until now. I plan to go with either a Koyo or a CSF from BHR.

Iíll get pictures of my plugs this weekend and post them. Iím assuming they should be clean though since I replaced them 2k ago
OK. Those are the only 2 radiators you should be considering, and even with those, cooling improvements are slight. The known good fan shrouds are 2 models from Flex-a-Lite.
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Old 02-09-2019, 04:34 PM
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Originally Posted by Steve Dallas View Post
OK. Those are the only 2 radiators you should be considering, and even with those, cooling improvements are slight. The known good fan shrouds are 2 models from Flex-a-Lite.
I will have to look at those closer to summer time. I definitely want to have one if I decide to drift/race it at a track. Out of the two, is the Koyo better or are they about the same?

Turned out it just wasnít properly burped. I think I didnít have it elevated enough to get the air bubbles out. I also made sure the heat was blasting too.
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Old 02-10-2019, 10:03 PM
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So I lied to myself. Got an OBD2 with Bluetooth to get some accurate temps. It wasnít fixed. When I had opened up and cleaned the SSV, I changed the thermostat to the mishimoto one. It wasnít installed correctly and thatís why I was overheating XP

got a 180F one and dropped it in correctly this time. Monitored it and stayed between 180 and 190F the whole time!
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