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Coolant Spilling Mazda3

I have a 2006 Mazda3 that is spilling coolant when the car is turned off. 127k miles

  1. I have changed the radiator cap 3 times
  2. Car does not overheat
    2a. Car does not seem to have the same peppy power it once had
  3. Temperature gauge never moves over half way up dial.
  4. Thermostat had been replaced.
  5. Car did overheat badly one time about 8 months ago. That is when repairs were done.
  6. Automatic transmission
  7. When car is running at a high RPM @5000 for 5-10 seconds car will hesitate and blow black smoke.
  8. Leak down test had been done twice on cylinders
  9. Catalytic convertor does not seem to be clogged

Thanks for your help.

When it sits the engine is heat soaked and temps and pressure goes up. You will need to get a flashlight and get under the car and follow the leak up. Feel around every hose. Check the radiator fins where the meet the end caps. It’s cone to take a little patience, but you’re lucky it’s an external leak and it should be easy to find.

It does sound like there may be some more serious engine mechanical problem awaiting you down the line, but I don’t think this coolant leak is due to that. As mentioned above, you need to determine where the leak is originating. A good bright flashlight and some visual sleuthing should be enough to find the source of the leak. It wouldn’t be at all unusual for a radiator to spring a leak at this age and mileage. Usually they leak where the plastic part on top (which contains the fill-hole where the radiator cap screws on) meets the metal part of the radiator.

Thanks for the help, but the coolant is co,ing out of the reservoir overflow. I have changed the cap 3 times to no avail. The only thing I haven’t tried is replacing the reservoir.
The car is not overheating and no head gasket or leaks have been found in the cylinders.
This problem has completely bamboozled 3 highly recommended mechanics. My last step is the mazda dealer, but I fear they will just want to throw money at it.

Hey guys, sorry for bumping this very old topic but I’m having this very exact issue. Podnick, did you ever fix this issue? Why did you think it’s the cap? Would really appreciate the help even though I know it’s been a while.

You need to click on Podnick’s avatar

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If you don’t do that, it’s very likely he won’t have any idea you’d like to talk to him

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It could be a head gasket leak. You can borrow a pressure test kit at some parts places (you pay for it, and they refund when you bring it back.) With it you can pump air pressure onto the radiator cap and see if it holds the pressure it is spec’d for. Then pump pressure into the radiator and see if the cooling system holds pressure. If it does not, there’s an external leak (likely visible) or an internal leak (likely a head gasket leak into a cylinder, and not visible.) If you get evidence of a head gasket leak, it can be confirmed by a hydrocarbon sniffer held over the open radiator cap while the engine is running (detecting unburned exhaust gasses bubbling out) or by chemical test strips that detect unburned hydrocarbons in the coolant.

Thanks for the advice! Tried that at first, but didn’t realize I had to hit trust level 1 first, so ima get to that. Thanks!

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5000 rpm? Showing my ignorance, to cars really go that many RPM? I think 3000 rpm is pushing the limit in the cars I have owned.

I have been suspecting the head gasket as well, as I have a lot of oil buildup in that same area (infact I have a huge line of black gunk on the bottom of my hood along there) Problem is that’s also the same location as the water pump, and just a little bit over is the resevoir cap. The radiator has no cap in this car, just the pressurized resevior tank. I assume that res. cap acts the same however. but not sure.
Other question: Does burning synthetic oil smell different from conventional? Cars been smelling funky lately and im not sure if that’s cause im burning coolant or because I’ve never experienced burning synthetic oil. Cause that would be a huge flag.

~6.5k redline on average. You won’t hit 5000 rpm on an automatic car driving normally unless you REALLY need to pass someone on the highway.
Some other type of mazda cars can get 7.5k :stuck_out_tongue_winking_eye:

I am sure it must vary between cars, but going 78mph with my 6 banger I think it is at 2300 rpm.