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Originally Posted by infernosg
I have noticed there is a tiny tear in one of the rubber seals in the radiator cap. I though it too small to make a difference but who knows. I always figured with the car running the pressure generated by the water pump would be more than sufficient to keep air from being sucked in, even at idle. If air is getting into the system with the car off, I'd expect to see the bubbles stop at some point as well.
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Definitely replace the cap with a new Mazda cap then. If it's not sealing properly, it won't hold its rated pressure, and this in turn will make it more likely to boil over.
Quote:
Originally Posted by infernosg
This I know. The rad. cap is the original I believe, but I'm almost certain the thermostat was replaced at one point (I have the records from the previous owners) and it's likely it's not an OEM Mazda unit. I'll do the pressure test and if that passes, change the radiator cap and go from there. If it fails, well I've got some exploring to do...
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If it's not a Mazda T-stat, I'd just replace it. The Mazda T-stat & gasket for it is pretty cheap, like under $15
Quote:
Originally Posted by infernosg
Yep, cooling system is all stock. I had no issues during the other runs over the weekend but I did stay in 3rd gear a lot more for this particular run so perhaps that was the proverbial straw. Aside from an upgraded radiator what other modifications would bring the cooling system up to track-ready levels? It's not a track-only car and I maybe drive it 25% of the time. I've seen underdrive main pullies but those make me nervous with the stock alternator's output.
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Besides an upgraded radiator, just make sure the fan shroud and all the ducting is in place & functional, including the plastic undertray. Key point here is to make sure that air only flows thru the radiator & oil cooler, and not around them. As for the fan, it only matters when you're at idle or driving at low speeds, but just check it per the FSM procedure to verify the clutch on it works - when it's hot, fan should turn but resist freewheeling when you try to spin it by hand. The underdrive pulleys will help reduce waterpump cavitation at high RPMs on your track days, and if paired with a similarly sized underdrive alternator pulley (i.e., to keep the drive ratios the same/close to stock pulleys) would solve any alternator output issues. Anything else is just maintenance - flush out your system regularly, use fresh coolant & distilled water at proper mix for your climate, check/replace all hoses as required.
Quote:
Originally Posted by infernosg
Is there any way to "officially" bleed the S5 cooling systems? I open up the heater, turn the car off, then fill the radiator and overflow bottles. I squeeze the upper radiator hose to get as many air bubbles out as possible.
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Not that I can find in the FSM. What I do whenever I flush & fill the system is make sure the heater is set to full heat before starting, and after I do the initial filling of the radiator with coolant, I'll let it idle with the rad cap off. When the engine reaches operating temp and the upper hose is hot to the touch, I'll run the engine in neutral at a constant 2~3K RPMs for a couple of minutes, then I'll quickly rev the engine up past 5K & back down to idle a few times, still with the cap off. When the level in the radiator drops (it will as trapped air pockets escape), add more coolant till its full. While you're doing this drill, the coolant level buzzer will sound off from time to time - it's normal. I keep repeating this process until I can't add any more coolant to the radiator. Then I top off the overflow tank with coolant to the full line, put the radiator cap back on, and take it for a drive. Let it cool down fully, check the level in the overflow tank, add coolant if needed to get it back to the full mark.