overflow bottle

iam going to get rid of that piece of junk plastic overflow bottle, because the caps would never stay tight, but is it normal for the bottle to expand and look like its going to explode? it does that then the cap comes loose, and never goes back on tight again, i went through two of them that did the same thing. i think its because its getting to much pressure. could this by caused by a blown head gasket?

check the hoses running between the t-stat housing and the heater core/pressure bottle for blockage.

I kept blowing caps off of mine violently and couldn't figure it out until I just tore everything the hell apart and found one of those t-connectors to be blocked.

It wouldn't let air escape to the bottle and caused the system to boil over easily.

I've got a dent in my hood from the cap blowing off. scared the fawk out of me. a loud bang and a bunch of "smoke"



(you could also have air trapped in the system, or your radiator isn't doing its job)

a blown head gasket would keep the system from building up pressure, if anything.

The plastic bottle was a bad design. When overheated, the platic would warp and the cap would not make a tight seal again - it just kept turning.
I resolved that by replacing it with an aluminum bottle by moroso. See www.summitracing.com part # mor-63651 ($99)
I had to get some brass npt fittings and a 16-18lb. radiator cap. I plugged the overflow tank fitting (the stock bottle did not send to an overflow tank, and neither should this one).
The benefit is that it will hold MUCH tighter than the stock bottle and there is no plastic to warp.

Note: higher pressure = higher boiling point. At sea level the boiling point is about 212 degrees, and at 1mile high, the boiling point is about 203 degrees. For every 1lb of pressure on the cap, the boing point increases by about 3 degrees.
Therefore, if you're at sea level (212) and put on 16lb radiator cap, the boiling point increases to about 260degrees. Antifreeze will increase that number even further.

With a radiator pressure tester (about $80) you can test for a head gasket or cracked head problem. It should come with instructions for doing this. See www.stant.com part number 12270.

RTicUL8 said:

I plugged the overflow tank fitting (the stock bottle did not send to an overflow tank, and neither should this one).

Click to expand...

Sorry, I have to call SPOBI on this one. Since I believe I was the first person in to do this conversion, I think I understand how it works.

The plastic bottle is filled only halfway, so as system pressure builds up the air in the top of the bottle simply compresses. That's why you don't have an overflow/recovery bottle. (That also may explain why some people keep blowing caps -- the bottle is supposed to be filled to the top of the little post inside, which is about half full. If you fill the bottle to the top, there's no room for the coolant to expand.)

The Moroso tank with a radiator cap essentially changes you from a "closed" (sealed) system to an open system. Sure, you can plug the outlet that's intended for an overflow bottle. But then you have to be sure to only fill the Moroso tank halfway so the system has some space for expansion. This leaves air in the system.

It's much better to put a barb fitting in that hole and run a tube to a catch/recovery bottle. Then you can fill the tank all the way to the top and have a cooling system with no air in it. As the cooland heats up and expands, the excess goes into the overflow bottle, and as the system cools down the excess is then drawn back into the system.

If you install the Moroso tank with an overflow/recovery bottle, you basically convert from a closed to an open system while still retaining the original sensors, etc.

Eagle:

I'll give you FULL credit for doing this first. In fact, your post was the one that convinced me to purchase the moroso bottle.
THANK YOU!
At first I did install the overflow tank, and filled the expansion bottle only 1/2 way. I don't know what I did wrong, but what would happen is that after I stopped the engine, the coolant would boil. It filled the overflow tank until it blew out the small air inlet hole. What I think happened was that by adding an overflow tank no pressure at all could be kept in the system. Lower pressure = Lower boiling point.
Now it's running at higher pressure and a higher boiling point.
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I have a 16-18lb cap on it, but it does not get that high.
I purchased the Stant pressure tester (see link above) and it only builds up to about 12lb.
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P.S. I did make sure that the block was purged of air: By facing the front downhill and releasing all air at the temp sensor at the back of the block.
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P.S.S. I did find another problem that caused my XJ to overheat. And that was a bad cat and muffler. The baffles were coming apart and partially blocking the exhaust. Most of the heat from the engine dissipates thru the exhaust - something that took me a while to realize...

If you run the Moroso tank with an expansion/recovery bottle, the Moroso tank should be full when the system is cold. Just like on the new systems the radiator is filled to the neck when cold. The pressure cap still keeps pressure in the system -- "excess" coolant cal escape to the catch bottle only when the pressure gets high enough to open the pressure cap. I think you had other problems.

One of the problems is that if the system doesn't start out full, when it expands it's not pushing coolant into the recovery bottle, it's pushing air or steam. So unless you had enough coolant in the catch bottle to replace that volume, you'll then suck air back into the system when it cools down.

Properly installed, it should be impossible to run the Moroso tank half full with a recovery bottle. Why? Because every time you shut down and let it cool, coolant will be drawn back from the recovery bottle into the system. As long as you keep the recovery bottle 1/3 or so full, the system becomes self-burping.