The CFR SCCA hosted an autocross and track sprint at Florida International Rally Motorsport Park (The FIRM) this weekend. I decided to give the track sprint a shot after realizing the autocross was sold out. The attendance list was pretty low at only 45 drivers. They said that this was only their 2nd track sprint that CFR SCCA has hosted, so maybe that’s why the drivers list was so short? Regardless, the event was pretty smooth; we got 4 runs in and they even let us take a cool down lap in the middle. Here’s a YouTube playlist of all 4 of my runs.
It’s been a few years since I’ve done any track events with the miata. I did a HPDE event at Pitt Race shortly after turbo charging the car in 2017. I had overheating problems after ~3laps. Since then, I’ve gotten rid of the stock radiator, did a coolant reroute, and added ducting. I haven’t had overheating problems since. I only did one other track event after that, and it was a track sprint at Summit Motorsport Park.
The miata handled the Florida heat fairly well. Heat soak wasn’t really an issue, considering that we only run 1 lap at a time at a track sprint. I guess it doesn’t help to run the car hard and then park it right afterwards either though… I wish my data logger was working that day, but I could visually see coolant temps reach as high as 205F. Intake temperatures were about 120F/200F post/pre intercooler (taken just after crossing the finish line).
I have the check engine light programmed to turn on when the engine coolant temperature goes above 210F, and I noticed the light flicker a few times on my last lap. After parking the car in paddock, I opened the hood to take a look around. I saw some fluid marks on the brake booster, but it wasn’t much and looked dried up. At the time, I thought it was oil spraying out of the dipstick tube from blowby. I hung around and talked to some folks before packing up and driving home.
The drive home is about 2.5hrs, and was going well until I pulled off to get some gas. I noticed the over temp light coming back on again while I was waiting at a traffic light. I looked at the my digital dash, and sure enough the coolant temps were rising above 210F. After filling up on E85, I stopped at McDonalds to let the car cool off a little and so I could get some food. Afterwards, I checked under the hood again. I made sure the cooling fan was kicking on properly. I also inspected the grill to make sure there wasn’t a plastic bag or something blocking air flow; nothing. I checked the water pump belt tension; seemed fine. I wanted to check the coolant level too, but didn’t want to risk popping the cap while the system was still warm. There was still nothing obviously wrong, so I decided to hit the road and see how it behaves.
The coolant temperatures were just fine if I kept the car at speed. I didn’t have any issues until I hit traffic, slowing us to a crawl. I watched the digital dash, and sure enough the coolant temp slowly rose. I watched it get to 220F before I decided to pull off and check things out. Yet again, nothing looked obvious wrong from the outside. I started to think maybe it was a bad sensor, but that wouldn’t explain why it was fine at-speed, and then overheat once it slowed back down. I got back in the car, and luckily traffic let up a few minutes later. The car cooled right back down to about 190F once it was >60mph. I was able to make it home with no other hiccups. I parked the car and decided to dig into the next day.
The first thing I did was open the radiator cap and inspect the coolant level. Sure enough, it was about half a gallon low. I went to harbor freight and picked up a coolant pressure tester to see where the leak was. After connecting the tester and pressurizing the system, it was obvious that one of my old (probably original) heater core hoses had cracked. I also found out that I had “double stacked” rubber hoses to make an undersized barb fitting work with the original heater core hoses… oh the stuff you forget you did. I replaced the hose, and installed a properly sized barb fitting. After the system was fully put back together, I decided to give water wetter a try. I mixed 6oz of water wetter with ~1.5 gallons of tap water. Burped the system, and then re-pressure tested it. The system could easily hold 18psi of pressure now!
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