Coolant going to reservoir thereby depleting coolant capacity in the radiator

Tiny
WANKEL
  • MEMBER
  • 1988 MAZDA RX7
  • 1.1L
  • 4 CYL
  • RWD
  • MANUAL
  • 84,600 MILES
Took car for a drive and after about eighteen minutes of driving, the "add coolant" indicator illuminated on the dash. When I pulled over to inspect under the hood, the reservoir was full of coolant. The normal level of coolant in the reservoir is about 1/4 to 1/3 of the reservoir's capacity. After I let engine cool down, I opened the radiator cap, and added coolant to the radiator. I drove another fifteen minutes or less, and the symptoms repeated themselves. I could not detect any leaks other than the exit tube of the reservoir. I pressure tested the radiator cap and the cap appeared to hold pressure. I checked the color of the coolant in the reservoir and I did not detect oil in it. I checked the oil dipstick and the oil was not contaminated. I would appreciate it if you can lead me in the right direction in finding the defect.
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Friday, August 18th, 2017 AT 9:13 AM

4 Replies

Tiny
HEYMAN1104
  • EXPERT
I used to have one of those little cars. Loved it, but could not afford to keep it running. Anyways, your thermostat is probably stuck. The cooling system pressure is building and pushing the coolant out through the reservoir. Change the thermostat and let us know how it does.
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Friday, August 18th, 2017 AT 2:23 PM
Tiny
HEYMAN1104
  • EXPERT
Love your username, by the way. First name Felix?
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Friday, August 18th, 2017 AT 2:25 PM
Tiny
WANKEL
  • MEMBER
Maybe I need to recheck the radiator cap? The overheating starts at about 15 miles of driving.
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Wednesday, August 23rd, 2017 AT 7:29 PM
Tiny
HEYMAN1104
  • EXPERT
1 - Do the thermostat. I'm sure that it's your problem. Even if it wasn't at the beginning, overheating the engine probably damaged it.

2 - Being a Wankel engine, you're not going to get coolant in the oil or vice versa. At least that's my limited understanding of them, because there's no cylinder head, and no cylinder head gasket to leak. The only way it would mix the two things is if there was an oil cooler running through the radiator that was leaking (there's no oil cooler).
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Wednesday, August 23rd, 2017 AT 7:39 PM

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