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Discussion Starter · #1 ·
Does anyone know the purpose of the plastic wing nut on the top of the Elise OEM coolant reservoir?

My coolant level has been funky for a while in that it goes lower and lower the longer the car sits but then seems to come back to where she started when she warms up. Although when cold, it is always below the minimum line. I have had a faint whiff of coolant in the cockpit sometimes. So I was guessing a small leak was letting air into the system which was then working its way up to the tank over a multiday time frame. And I was guessing that since the system is mostly closed (I think) that extra air sitting in the reservoir would (when the car was running) get dispersed back into the system and cause the reservoir level to revert to its earlier (higher) level).

Feel free to tell me none of that make any sense! But I do have a question.

Although the right side of the reservoir had been dropping, the left side had always stayed full. With the engine stone cold, I loosened the plastic wing nut and both sides dropped dramatically. Almost to the bottom. So is that some kind of bleeder to let air vent out? When that happened, I pulled everything I could think of save the front clam to poke around and found some signs of leakage on the passenger side radiator hose where it connects to the pipe in the side rail and tightened that down (almost two full turns). Put some distilled water in the reservoir and started it up. When the dash gauge read about 185 or so, the radiator hoses became warm. Seems to be working fine. No history of overheating.

I will soon be pulling the rear clam and plan to replace the thermostat, put in a Radium swirl tank and flush the coolant (Toyota Red which finally arrived via Amazon). But for now, I am just wondering if running the car (driving up and down some hills) and topping off the reservoir in between jaunts will be enough to evacuate any air in there. And if the wing nut is a useful tool in that process. I do see the bleed fitting in the hose that sits lower than and behind the reservoir. Should I open that up until fluid runs out? The bleed fitting on the passenger side radiator hose is odd in that it is a Schrader valve. I guess that would work, although I wonder if its internals can stand up to constant exposure to hot antifreeze. Doesn't appear to be leaking now. I have no idea why a PO would make that change. I know BOE includes a Schrader valve in their swirl tank to pressurize the system, but wouldn't think one should be in the hose. I believe the radiator hoses are silicone (see photo) and those must have been installed when a PO put in the Pro Alloy Radiator (for which I am grateful).
 

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There is a ton of information here and at the Sands Museum about changing out the coolant which includes how to elevate the car to allow air to escape from the various bleeder screws in the lines. One of the tools draws a vacuum to then suck fresh coolant into the system. Drawing this vacuum will tell you if you have a leak but you already know you do, just not where. Check your oil for signs of water.

I did go with the BOE tank (warning, it does not work with the factory airbox). I've had the BOE tank for several years and several track events. No issues.
 

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Discussion Starter · #3 ·
Many thanks. The oil looks normal and its volume has not increased and she runs fine so I don't think there's an issue there. I have an Airlift II that has been sitting in my basement for a while as I screw up the courage to tackle that. As I am changing to the Radium, I also picked up a cheap little Mityvac ($47 from Amazon) to be able to do a pressure test. So that will be the next step. Could use that on the OEM tank but only after picking up an adaptor for $78! Although at this point, I think tightening down the hose connection to the pipe in the sill that returns from the radiator stopped the leak. I drove around a bit and made use of what I think is the bleeder on top so I think I got out most of any air pockets out and the fluid level is totally stable. I am thinking the Mityvac might be a nice back stop/adjunct to the Airlift.
 
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