Overheating Mirage

[Sulley]

Ok so I drove the Mirage tonight. Ran great but what seems to be happening is it hits about 200 degrees then when I turn it off I get antifreeze coming out of the radiator overflow hose. Does this mean I have air trapped in the system? I don't have a 'purge' tank. It ran fine before I opened up the cooling system. I replaced the hoses and had the radiator gone through. Now I keep getting this same issue.

[Blueovalz]

I would say yes. Finding a location (highest point in the system) in which the air can be bled off while the engine is hot (releasing pressurized air in the coolant system), then allowing the system to draw water back out of the reservoir as it cools down. This is where a purge tank is really useful (if I'm correctly using the purpose of that tank). I eventually purchased the AirLift product, which has been a godsend in being able to fill the system, and no longer having to burp, refill, rinse and repeat each time I perform maintenance on the coolant system.

[Sulley]

I found what I believe to be the system on Amazon. Is this the product? Looks like it is getting amazing reviews.

1) One end goes onto an air-compressor, where does the other end connect to?
2) Also, I would still need a purge tank with this. It's not like this tool eliminates the need for that correct?
3) Last Q - the current set up has the overflow from the top of the radiator. I assume I would not run a really long hose to the rear engine compartment for a purge tank that I would want to establish this in the engine compartment correct?

Thanks and sorry for all the questions. I'm pretty good at turning a wrench but don't know how the cooling system needs to function properly.

[Blueovalz]

That tool reduced my refill and burp time from a day's worth of attention to about 15 minutes (that's with set-up and clean-up if you're really good at it).
1) The compressor blows through a venturi and out a baffle. The venture effect results in a 25 inch (water) of vacuum on the entire coolant system. It will even depress hoses in the system when this vacuum is applied. The user has the option of testing the coolant system for leaks because that vacuum will be lost over a matter of a few minutes if a leak is present. Anyway once the vacuum is attained (about 1 minute of compressor blow-through), the coolant pickup tube is placed in a container full of the anti-freeze, a valve is opened, and atmospheric pressure pushes the coolant into the evacuated coolant system. By the time the vacuum in my experience is reduced down to 5-10 inches, I've sucked up two gallons of antifreeze into the engine through a tiny 3/8" hose in about 3 minutes...that's how well it works. I've never had to burp it using the AirLift product, and never have overheating due to air in the system.

2) You must have a means of allowing water to move into and out of the coolant system. As long as you have an overflow tank, you should be fine. You will need that to allow water to expand out of the system (warm-up), and to be sucked back into the system on cool-down. I'm not sure on what the difference is between a purge tank and an overflow tank, but you will need at the very least, a reservoir with a small tube that allows water past the radiator cap in both directions, into and out of the system.

3) In your system, if the top of the radiator is not the top of the entire system, AND it has lower points separating the two higher points, you will probably be able to eventually burp all the air out, but it will take multiple hot/cold cycles and fluid cycles in order to capture all the air into the top of your radiator (if that is possible at all). I had the same issue with mine, and had a plug at the top of my radiator (to burp with), and the overflow was at the engine in back. Again, with the AirLift, I've never had to burp the front radiator bleeds due to overheating issues you're describing. In my opinion, the overflow should be where the air is best collected in the system, which would be the highest point, which is probably at the engine. I believe one of our members (Andrew?) has installed a hose or tube from the radiator all the way back to the motor. Doing this does help ensure that the air trapped in the radiator will get back to the higher engine levels.

[Sulley]

Ok so I found this product that I think may be a solution.

http://www.jegs.com/i/Aerospace/026/...4OUxoChLDw_wcB

What if I installed this product with an overflow tank. That would give me the expansion that I need plus help eliminate trapped air in the system.

Q - if I install this do I need to do anything to my existing radiator? It has a cap and an overflow line. Does the radiator need to change to a completely closed system? Do I need to plug off the overflow line?

Thanks in advance and hopefully this will serve as a record for others.

[Blueovalz]

That is similar to what I'm using only in that I have two radiator caps on my car. I use a higher spring pressure on the front (at the radiator) that will not release pressure before the rear one (at the highest point just behind the engine) would. I've inserted a NPT plug in the front radiator fitting, but that isn't necessary if you use a stronger spring on the front cap. This is because the lower spring-pressured cap at the engine (the Jeg's piece) would be doing all the releasing and redrawing of water into a reservoir. With the Jegs part you've linked, my guess is that on warm-up, air will be pushed out (through the hose barb fitting) into a reservoir due to the cap action, and then liquid water drawn back in upon cool-down. It may take a few cycles to get all the air out (and you'll need to ensure the reservoir stays about 1/2 full -at cold- throughout the entire process). With a front radiator cap, you could crack the radiator cap to release any pocket of air in the radiator, and then seal it back down to let the rear cap to its work.

[Sulley]

Blueovalz thank you for all the technical wizardry! I have a 25 lb cap on the front and what you are saying makes total sense. I'll order this part and use that with an overflow tank to resolve (hopefully) my overheating and air pocket issues on my Manta Mirage. I'll post some pictures when I finally get all this in place and how it works.

[Manta22]

Overheating can be caused by several things either individually or, more likely, a combination of problems. A stock SBC water pump works fine in its original front- engine application where the radiator is only a foot away but in a Mirage, the coolant must be forced through one lower chassis tube, through the radiator, and back through another chassis tube. This system produces more restriction and back pressure on the water pump which reduces flow and this raises the coolant temperature. A better water pump such as an Edelbrock or Stewart pump is a big help in improving the flow.

A decent electric fan(s) is also a necessity for driving in traffic. The junction of the tubing stubs with the chassis tubes should be checked to see if the hole is clean or is a small ragged hole.

[Sulley]

Neil would you be able to link to a water pump that you would recommend? I've also thought about an electric one. So far I've had success but need to lower my radiator cap at the engine as the overflow is happening at the radiator when I stop. So I assume if I lower the psi cap at the engine it should overflow there where I need it to.

[Blueovalz]

One issue I had when getting the various caps online, was that many vendors do not state the diameter of the cap. Several times I received caps that were too small a diameter to fit (how was I to know?).