Hello, I have a 2004 Mazda RX8, I have a overheating problem which just recently started. For the last week, I noticed that I had to fill the overflow tank everyday. The car is not overheating, but the overflow tank ligh has been coming on. The temp gauge is reading normal while I am driving. whenever I reach my distanation the overflow tank starts boiling over and spilling hot water. The fans are on and working. I let it cool down and fill it up water again only for it do the same thing when I drive the car somewhere else. I am driving my car about 10 or 15 miles. If I'm driving it down the road to store I have no probem. Does anyone have any ideas what might be causing this problem? I am thinkling waterpump.

 

Let your car cool overnight and then check your coolant level. If it is below the Full mark add coolant to the full mark or just above it. If your coolant level is fine then is sounds like youe coolant sensor is going bad. And the only way to fix the problem is to replace the oem coolant tank since the sensor is built into it.

 

I reach my distanation the overflow tank starts boiling over and spilling hot water. The fans are on and working. I let it cool down and fill it up water again only for it do the same thing when I drive the car somewhere else.

Sounds like your coolant sensor went bad and you thought you needed to add more coolant. Now there is too much coolant and it is overflowing. And you keep adding more so it keeps on overflowing.

 

Learn how to search, there are many threads on this problem.
https://www.rx8club.com/search.php?searchid=5301254

 

I just replaced the tank with sensor about two months ago. what I don't understand is where is all the water going. I don't have a leak and why would the water tank be boiling over.

 

when the light is on, the tank is empty, I don't think its the sensor. Everytime I fill the tank, I fill it to the to proper level and after reaching my distanation, it;s still boiling over

 

Besides during start up do you have white exhaust smoke?

 

I've had white smoke a few times, not all the time. most of the time it starts up ok no smoke

 

The coolant light only comes on when the coolant level is low i would bring the car back to the dealer and tell them this wasnt happening before you put the new coolant overlfow tank in

 

I replace the tank, myself, do u think the motor cylinder might have a crack or could it be the water pump

 

wat he saoid

 

First off, what a motor cylinder? You should fill it up and let run until it warms up and check to see if you have an obvious leak anywhere.

 

I was thinking it was called a motor cylinder instead of an engine block, regular engines have a block and heads, If the heads are crack it could cause the vehile to overheat, but this vehilce has no heads. no leaks anywhere

 

This engine has rotor housings and coolant seals, if a coolant seal is blown then you would leak coolant. Problem is there are inner and outer coolant seals, if an inner seal failed you leak coolant into the engine if an outer seal went you would leak coolant outside the engine.

 

any power loss?
exhaust fumes smell sweet?

 

no the car runs fine, no sweet smell, its not overheating while I am driving, but once I turn off the vehile, the overflow tank well be boiling over with hot water

 

bad radiator cap?
thermostat failing?

water pump isn't leaking? check any signs of leakage from coolant lines.

 

replaced thermostate and cap a few months ago. I have no leaks. I am thinking water pump what do u think

 

I'm with this idea .

 

wait. wait...

Is your car overheating??? Just because coolant is boiling out of your overflow/coolant tank doesn't mean it is over heating. Has your stock temp gauge moved at all during these trips?

If not, than you just don't have the proper level of coolant in your system and some will boil off, and upon start up, it'll suck more into the system emptying the tank.

It took my car about 5 days to get all the air out of the system and to get the right amount of coolant in the system after I swapped my water pump and thermostat and flushed the system. It would boil over a bit, and then cold it would be low again...

It doesn't sound like you're over heating; it sounds like when you replaced the coolant bottle, air got into the system and now its trying to purge the air and get the coolant levels right.

 

I think the engine is bad. Remove the over flow cap and fill coolant to proper level. Start car with cap off and let the car warm up to operating temp. Watch the water in the coolant tank. Please use safety glasses when doing this. If you see small bubbles and foam in the overflow tank then the coolant seals are bad and it's time for a new engine. Have someone raise the engine rpms a couple of thousand and you watch the coolant in the tank.

 

Silly question.. you've said water a few times, rather than coolant. You're using 50/50 coolant/water mixture, right? Not just straight water...?

 

Not necessarily.... You have to know the difference between burping bubbles and a leak.

Burp it by putting it on an rear incline and running it with the cap off.

 

Just because the bottle was changed two months ago, doesn't mean it's not the sensor again. Where did you get the collant bottle and do you know what revision it is? They are up to "M" and maybe you got sold an earlier one?

Also..............this is going to be silly, but where do you see the water/coolant boiling over? Is it from the coolant overflow hose?
Do you know where the full line is on the bottle?

I'm still with some others thinking you are over filling it constantly. If it was a seal, you'd think you would see or smell something and/or have other issues.

I'm also with the person that asked if you are just running water and not coolant?

 

Could be. My 2nd engine would leak coolant into #2 rotor. After setting overnight, coolant would collect and cause the engine to sputter for a minute or two. After that it would be fine. Other than a small coolant loss, those were the only symptoms.